Electrical Is the Kings 200W blanket really value for money??

[Macca_75]

So following on from my newly found knowledge of Solar, Batteries and everything in between I ask myself are the 200W blankets with the supplied controller really the value they seem?

I tested my blanket with no controller/load attached - it had an open voltage of 24.9v. This was on a clear day when the sun was directly overhead and the blanket laying flat.

Ignoring losses for cable quality, etc I *think* the below is correct.

Since the PWM controller clips this down to 13.5 (not programmable) you can only ever harvest approx 24.9/13.5% ~ 55% or the claimed 200W, or 110W.

Where you *may* get some of the value back (over a smaller blanket) is when you are in less than perfect conditions (ie. you may only be harvesting 18V - where a smaller rated panel may only harvest 14V (which is not enough to turn the controller on)).

Just my thoughts.

Once I get the MPPT charger I've love to do a comparison between the outputs "in perfect and not perfect" conditions and compare a better controller (and see if the value is really there for a better controller).

 

[Boots in Action]

So following on from my newly found knowledge of Solar, Batteries and everything in between I ask myself are the 200W blankets with the supplied controller really the value they seem?

I tested my blanket with no controller/load attached - it had an open voltage of 24.9v. This was on a clear day when the sun was directly overhead and the blanket laying flat.

Ignoring losses for cable quality, etc I *think* the below is correct.

Since the PWM controller clips this down to 13.5 (not programmable) you can only ever harvest approx 24.9/13.5% ~ 55% or the claimed 200W, or 110W.

Where you *may* get some of the value back (over a smaller blanket) is when you are in less than perfect conditions (ie. you may only be harvesting 18V - where a smaller rated panel may only harvest 14V (which is not enough to turn the controller on)).

Just my thoughts.

Once I get the MPPT charger I've love to do a comparison between the outputs "in perfect and not perfect" conditions and compare a better controller (and see if the value is really there for a better controller).

Not quite right @Macca_75 . The PWM controller does not clip the voltage. It does limit charging voltage down to just above battery voltage (for it to charge a battery) . Example - if battery is low at 12.1 volts, then PWM will apply 12.2 volts to battery, any excess voltage (17 or 18 volts minus 12.2 volts - approx 5+ volts) is siphoned off through resistors etc and not used. Of course, this changes as battery voltage increases so more watts are available, but this is the advantage of MPPT charging. You get MORE when you need it most (battery low)!! 12.2 volts by 8.0 amps equals 97 watts usable in PWM, as against 18 volts by 8.0 amps equals 144 watts available produced by solar panel for MPPT. The MPPT converts the total available watts (144 ) to 11.8 amps at 12.2 volts (still the same 144 watts) disregarding less than 5% loss in doing this.
Most PWM controllers have a fixed max charging voltage of around 14.4 volts and the PWM will continue to charge battery until it gets to that set figure before dropping back charging (on/off switching) to stabilize the FLOAT voltage usually 13.7 volts. As you said these settings are non- adjustable in most PWM controllers, but the better ones do have user selectable settings. All the good MPPT controllers let you adjust these settings to you own choices including battery type.

The attached link may be helpful to you. Cheers

 

[Drover]

So many things come into play when you try to evaluate these sort of things, type of controller is important but quality can play a big part, the label stating MPPT is not always to be believed and the controller is only part of the package, crappy connections, poor cable and just general rubbish fit out won't help no matter how much money is thrown at it............ If your battery has a dogs breakfast of cables hanging off it then its a poorly designed and probably isn't efficient.....

To work out the possible amp output of your panel, on the label it will state the watts (stated but not real) divide this figure by the vmp rating given in volts, this will then give you the amps you could possibly get out of the panel .............. no matter what it hooks up to you won't really achieve that even if you fitted it to a sun tracker...

The Kiss method of setting up means if you need to constantly check what your set up is doing and are worried about charging then you have a major problem in that your system is too small my vans set up draws 25% of my capacity daily at the most, thusly I look at my meter in morning and evening out of interest not of neccessity.......... Plenty of storage, plenty of supply that requires minimal attention and can be left to operate on its Pat Malone is what is needed for off grid and not having it all in one basket, because if the handle falls off it fails, the option to remove a failed section but still work is optimum for a good system.........

Not having a go at you Macca just putting it out there in general, @Boots in Action has done a very complete tome on PWM v MPPT testing so don't ask him about it or we will run out of data again...just joking Booties...........

A link to a very informative peice which some don't quite agree with but the writer is a respected writer on the subject not a social media scribbler.https://www.gorv.com.au/10-rv-solar-myths/

 

[Boots in Action]

So many things come into play when you try to evaluate these sort of things, type of controller is important but quality can play a big part, the label stating MPPT is not always to be believed and the controller is only part of the package, crappy connections, poor cable and just general rubbish fit out won't help no matter how much money is thrown at it............ If your battery has a dogs breakfast of cables hanging off it then its a poorly designed and probably isn't efficient.....

To work out the possible amp output of your panel, on the label it will state the watts (stated but not real) divide this figure by the vmp rating given in volts, this will then give you the amps you could possibly get out of the panel .............. no matter what it hooks up to you won't really achieve that even if you fitted it to a sun tracker...

The Kiss method of setting up means if you need to constantly check what your set up is doing and are worried about charging then you have a major problem in that your system is too small my vans set up draws 25% of my capacity daily at the most, thusly I look at my meter in morning and evening out of interest not of neccessity.......... Plenty of storage, plenty of supply that requires minimal attention and can be left to operate on its Pat Malone is what is needed for off grid and not having it all in one basket, because if the handle falls off it fails, the option to remove a failed section but still work is optimum for a good system.........

Not having a go at you Macca just putting it out there in general, @Boots in Action has done a very complete tome on PWM v MPPT testing so don't ask him about it or we will run out of data again...just joking Booties...........

A link to a very informative peice which some don't quite agree with but the writer is a respected writer on the subject not a social media scribbler.https://www.gorv.com.au/10-rv-solar-myths/

Thanks for your back up there @Drover in explaining that there are many other variables involved in solar charging - heat on panels, battery temperature, voltage losses in cables and connections, angle to the sun and solar panel efficiency too etc. All so true. Both of us are "in tune" in trying to help others on this forum. I don't know about running out of data...again... though???? Regards

 

[mikerezny]

You are sort of on the right track. However, you cannot use the Open Circuit voltage (Voc) in your calculations. As soon as current is drawn the panel voltage will go down. Somewhere between an Open Circuit (Maximum Voltage, Voc) and Short Circuit current (Isc) will be the sweet spot.
Maximum Voltage is with no current so the panel will deliver 0 W, similarly with short circuit current, the voltage will be zero, so again 0W.
The maximum power is obtained by loading the panel so that a voltage of Vmp (Voltage at maximum power) is achieved and should then deliver Imp (Current at Maximum Power). If you do the calculation that will be a little more than the rated wattage of the panel.

Voc, Isc, Vmp, and Imp should be shown on the certificate on the back of the panel.

It is difficult to calculate, given the panel specs, what a PWM controller will deliver into a battery, since it is just a fast switch where the duty cycle is controlled by sensing the battery voltage to ensure the battery is charged correctly. But it will not be optimal. i.e. it unlikely to be running the panel at Vmp and Imp. Any loading either side of this optimal setting will deliver less power from the panel.

An MPPT controller has two distinct parts. But it is basically a switch-mode DC-DC converter. It has a sophisticated algorithm that finds a load to put on the panel and then perturbates it slightly in each direction. It measures the power output on either side and if one side delivers more power it shifts to the new loading. That is the input side, the output side monitors the battery voltage to ensure it is being maintained at the correct voltage.

All of this is assuming you need the maximum power that the panel can deliver. So it is really an efficiency exercise do you pay more for an efficient MPPT controller or just buy more solar and keep a cheaper PWM controller for the same outlay.

But if you have added plenty of margin in the design of the solar system to easily recover your batteries, it really matters not whether you have an MPPT or a PWM controller since both will probably not need to work to capacity to recover the energy used.

But again there is the consideration of weight and size. Normal solar panels are heavy and take up a lot of roof area. If one is concerned with keeping weight down in a van, or cannot find enough roof space to mount enough solar, then it becomes a no brainer. An MPPT controller will deliver more power than a PWM controller from the same panel.

If you are going to get into this in detail, there is much more to measuring solar performance than just measuring the current going into a battery. You will need to understand that a battery is not a constant load, as soon as you start charging it, the voltage rises and the battery charging side of the controller will cut down the current to maintain the voltage. You need to find some large load capable of sucking up the entire output of he panel. If you have a 200W panel, you will need to find something that draws 200W at 12V. Three 60/75W car headlamps, a 12V / 240V inverter with a variety of incandescent lamps etc.

Also note that panels are rated at a standard of 1000w / sq m and at 25C. One you put a panel in the sun it will soon be hotter that 25C making it difficult to do long tests. Similarly, it is difficult to keep the sun the same to do comparisons.

If you haven't got clampmeter that can measure DC current, it would be a good investment. @Boots in Action and I invested in the same one and would recommend it. They cost about $45 on eBay. Do asearch on eBay for Uni-t dc clamp meter.

Also, for about $15 you can get these little gadgets on eBay: They will measure current, voltage, accumulate Ah, accumulated watts, plus other things. A must have for anyone wanting to play in this area.

cheers
Mike

 

[Macca_75]

Not quite right @Macca_75 . The PWM controller does not clip the voltage. It does limit charging voltage down to just above battery voltage (for it to charge a battery) . Example - if battery is low at 12.1 volts, then PWM will apply 12.2 volts to battery, any excess voltage (17 or 18 volts minus 12.2 volts - approx 5+ volts) is siphoned off through resistors etc and not used. Of course, this changes as battery voltage increases so more watts are available, but this is the advantage of MPPT charging. You get MORE when you need it most (battery low)!! 12.2 volts by 8.0 amps equals 97 watts usable in PWM, as against 18 volts by 8.0 amps equals 144 watts available produced by solar panel for MPPT. The MPPT converts the total available watts (144 ) to 11.8 amps at 12.2 volts (still the same 144 watts) disregarding less than 5% loss in doing this.
Most PWM controllers have a fixed max charging voltage of around 14.4 volts and the PWM will continue to charge battery until it gets to that set figure before dropping back charging (on/off switching) to stabilize the FLOAT voltage usually 13.7 volts. As you said these settings are non- adjustable in most PWM controllers, but the better ones do have user selectable settings. All the good MPPT controllers let you adjust these settings to you own choices including battery type.

The attached link may be helpful to you. Cheers

@Boots in Action - Thanks. I get how the PWM controller "loses" excess voltage (I incorrectly referred to it as clipping) - basically the volts into the controller is reduced to match the batteries requirements at the time, but the Amps remain consistent.

When comparing to MPPT you quote 18v - where did you get this from (I tested my panel with no load/controller as being ~25v)?

@Drover - I'm talking specifically about quality MPPT controllers here and not some $30 re-badged ebay special dodgy one.

 

[Boots in Action]

You are sort of on the right track. However, you cannot use the Open Circuit voltage (Voc) in your calculations. As soon as current is drawn the panel voltage will go down. Somewhere between an Open Circuit (Maximum Voltage, Voc) and Short Circuit current (Isc) will be the sweet spot.
Maximum Voltage is with no current so the panel will deliver 0 W, similarly with short circuit current, the voltage will be zero, so again 0W.
The maximum power is obtained by loading the panel so that a voltage of Vmp (Voltage at maximum power) is achieved and should then deliver Imp (Current at Maximum Power). If you do the calculation that will be a little more than the rated wattage of the panel.

Voc, Isc, Vmp, and Imp should be shown on the certificate on the back of the panel.

It is difficult to calculate, given the panel specs, what a PWM controller will deliver into a battery, since it is just a fast switch where the duty cycle is controlled by sensing the battery voltage to ensure the battery is charged correctly. But it will not be optimal. i.e. it unlikely to be running the panel at Vmp and Imp. Any loading either side of this optimal setting will deliver less power from the panel.

An MPPT controller has two distinct parts. But it is basically a switch-mode DC-DC converter. It has a sophisticated algorithm that finds a load to put on the panel and then perturbates it slightly in each direction. It measures the power output on either side and if one side delivers more power it shifts to the new loading. That is the input side, the output side monitors the battery voltage to ensure it is being maintained at the correct voltage.

All of this is assuming you need the maximum power that the panel can deliver. So it is really an efficiency exercise do you pay more for an efficient MPPT controller or just buy more solar and keep a cheaper PWM controller for the same outlay.

But if you have added plenty of margin in the design of the solar system to easily recover your batteries, it really matters not whether you have an MPPT or a PWM controller since both will probably not need to work to capacity to recover the energy used.

But again there is the consideration of weight and size. Normal solar panels are heavy and take up a lot of roof area. If one is concerned with keeping weight down in a van, or cannot find enough roof space to mount enough solar, then it becomes a no brainer. An MPPT controller will deliver more power than a PWM controller from the same panel.

If you are going to get into this in detail, there is much more to measuring solar performance than just measuring the current going into a battery. You will need to understand that a battery is not a constant load, as soon as you start charging it, the voltage rises and the battery charging side of the controller will cut down the current to maintain the voltage. You need to find some large load capable of sucking up the entire output of he panel. If you have a 200W panel, you will need to find something that draws 200W at 12V. Three 60/75W car headlamps, a 12V / 240V inverter with a variety of incandescent lamps etc.

Also note that panels are rated at a standard of 1000w / sq m and at 25C. One you put a panel in the sun it will soon be hotter that 25C making it difficult to do long tests. Similarly, it is difficult to keep the sun the same to do comparisons.

If you haven't got clampmeter that can measure DC current, it would be a good investment. @Boots in Action and I invested in the same one and would recommend it. They cost about $45 on eBay. Do asearch on eBay for Uni-t dc clamp meter.

Also, for about $15 you can get these little gadgets on eBay: They will measure current, voltage, accumulate Ah, accumulated watts, plus other things. A must have for anyone wanting to play in this area.

cheers
Mike

Yes Mike @mikerezny , the more I use the clamp meter, the more I would not be without it now! Also above, a good summary for @Macca_75 to digest.

 

[Boots in Action]

@Boots in Action - Thanks. I get how the PWM controller "loses" excess voltage (I incorrectly referred to it as clipping) - basically the volts into the controller is reduced to match the batteries requirements at the time, but the Amps remain consistent.

When comparing to MPPT you quote 18v - where did you get this from (I tested my panel with no load/controller as being ~25v)?

@Drover - I'm talking specifically about quality MPPT controllers here and not some $30 re-badged ebay special dodgy one.

@Macca_75 , @mikerezny has just put forward a very good explanation of this. Perhaps have a good read and see what happens in this "white man magic".
Open circuit voltage is like a car idling under no load. The 18 volts is the loaded voltage usually available under light load. When under heavy load (charging at a high rate to a low battery), it could be a lot lower, down to 15 or 16 volts depending on quality of solar panels - efficiency and cell temperature. By the way, the panel does not reduce the voltage from controller to battery, it is adjusted by the controller to suit battery voltage.

 

[Drover]

.

I'm talking specifically about quality MPPT controllers here and not some $30 re-badged ebay special dodgy one.

Who was talking about a $30 special, I was meaning those that have $180 or more price tags, they sound good, the $30 specials be they PWM or MPPT are usually rubbish............................. some on here have bought the pricey as well as named solar blankets that are equally dodgy.........

Anyway all the info's there to make a decision now to see what happens away from the bench.

 

[Macca_75]

Thanks @mikerezny - I'll read and digest later.

I already have the KT Watt meter - https://ktcables.com.au/products/category/solar-panel-accessories/power-meters/ - really nice bit of kit. The anderson's are built into the meter to no cables, etc.

I have 1 fixed panel now on a 100/20 MPPT and will be buying a second smaller 75/15 MPPT for the blanket and the battery sense (so the 2 x MPPT's can work together without impacting each other). On any given day it's not normally an issue, but we are leaving for 6 months on the road and I want to make sure when we have a few overcast days we are all OK. Plan C will be running the car for a bit *if* I really need the juice.

Anyway - Thanks for the reading. I'll understand it a little later.

 

[Boots in Action]

.

Who was talking about a $30 special, I was meaning those that have $180 or more price tags, they sound good, the $30 specials be they PWM or MPPT are usually rubbish............................. some on here have bought the pricey as well as named solar blankets that are equally dodgy.........

Anyway all the info's there to make a decision now to see what happens away from the bench.

Steady there @Drover . Whoa!! For @Macca_75 , Yes my Powertech PWM controller 30A (approx $185.00) cost more than the MPPT controller I have now when I bought it years ago, when MPPT was relatively new. Technology has improved and made (proper) MPPT controllers cheaper!

 

[mikerezny]

Just my two cents worth....

Whether you buy a proper MPPT controller or a cheaper PWM controller rebadged as an MPPT controller has nothing to do with where it is bought.

It is just as easy to buy crap from anyone as it is to buy it on eBay. Similarly, many good retailers sell on eBay: Good Guys and autoelec are two that I have used.

Similarly with buying so-call Chinese crap. Try buying a phone, camera, iPad, or computer, that is better quality than what is manufactured in China. Every country has manufacturers that make crap. Most countries also have manufacturers that produce world-class goods. China is no exception.

The skill is in understanding the difference before making a purchase.

I spent 10 years retailing and wholesaling electronics and another stint as a technical product manager for professional products at Sony. There was a time when products made in Japan were regarded as Jap Crap, including their motorbikes and cars.

Hmm, I appear to have drifted off-topic. Apologies.

cheers
Mike

 

[Boots in Action]

Thanks @mikerezny - I'll read and digest later.

I already have the KT Watt meter - https://ktcables.com.au/products/category/solar-panel-accessories/power-meters/ - really nice bit of kit. The anderson's are built into the meter to no cables, etc.

I have 1 fixed panel now on a 100/20 MPPT and will be buying a second smaller 75/15 MPPT for the blanket and the battery sense (so the 2 x MPPT's can work together without impacting each other). On any given day it's not normally an issue, but we are leaving for 6 months on the road and I want to make sure when we have a few overcast days we are all OK. Plan C will be running the car for a bit *if* I really need the juice.

Anyway - Thanks for the reading. I'll understand it a little later.

Sorry to be the bearer of bad news @Macca_75 . Running your vehicle to charge your van battery will not really do the job of fully charging it. Your battery will need approx 14+ volts to do any real good unless you have a DC to DC charger. Not knowing what sort of modern vehicle, alternator charging voltages in modern tugs is not high enough to do any good. Have a look at the attached info from Redarc and see where your tug sits as regards alternator output voltage. hang in there - at least you will know the pitfalls!!

 

[mikerezny]

I already have the KT Watt meter - https://ktcables.com.au/products/category/solar-panel-accessories/power-meters/ - really nice bit of kit. The anderson's are built into the meter to no cables, etc.

Yep, that looks very similar. It should be very useful.

It does not seem to provide accumulated Ah or Wh. Accumulated Ah is quite important for determining the total Ah harvested or consumed over any time period. For instance, if you have a 100Ah battery, by measuring the O/C battery voltage without any loading, you can determine the State of Charge (SOC) of the battery. So, say you battery is down to 75%. You need to recover 25Ah during the day plus another 10-15% for inefficiencies., so say 30Ah.

If you can measure accumulated Ah from your panel you can determine if you have done a full recovery or not.

Morning SOC and solar recovery are pretty well all you need to determine if you have sufficient battery storage and solar capacity.

Monitoring these each day is also a simple and good health check on the entire 12V system.

cheers
Mike

 

[Macca_75]

Just my two cents worth....

Whether you buy a proper MPPT controller or a cheaper PWM controller rebadged as an MPPT controller has nothing to do with where it is bought.

It is just as easy to buy crap from anyone as it is to buy it on eBay. Similarly, many good retailers sell on eBay: Good Guys and autoelec are two that I have used.

Similarly with buying so-call Chinese crap. Try buying a phone, camera, iPad, or computer, that is better quality than what is manufactured in China. Every country has manufacturers that make crap. Most countries also have manufacturers that produce world-class goods. China is no exception.

The skill is in understanding the difference before making a purchase.

I spent 10 years retailing and wholesaling electronics and another stint as a technical product manager for professional products at Sony. There was a time when products made in Japan were regarded as Jap Crap, including their motorbikes and cars.

Hmm, I appear to have drifted off-topic. Apologies.

cheers
Mike

All good here. I buy most things of ebay - but also follow the rule "you get what you pay for". I used ebay as an example as I believe the majority of reputable online and bricks and motors stores would not (knowingly) sell the "false" MPPT chargers - ebay really is the wild west of bargin hunting, If you watch any YouTube video on a "false" MPPT charger where they tear it down you will almost always find it was "purchased from ebay"

I also have no issue with "made in China" (or Japan or anywhere else) - once again they can produce the highest and lowest of quality - you get what you pay for.

 

[Macca_75]

Yep, that looks very similar. It should be very useful.

It does not seem to provide accumulated Ah or Wh. Accumulated Ah is quite important for determining the total Ah harvested or consumed over any time period. For instance, if you have a 100Ah battery, by measuring the O/C battery voltage without any loading, you can determine the State of Charge (SOC) of the battery. So, say you battery is down to 75%. You need to recover 25Ah during the day plus another 10-15% for inefficiencies., so say 30Ah.

If you can measure accumulated Ah from your panel you can determine if you have done a full recovery or not.

Morning SOC and solar recovery are pretty well all you need to determine if you have sufficient battery storage and solar capacity.

Monitoring these each day is also a simple and good health check on the entire 12V system.

cheers
Mike

Cheers @mikerezny - I have the Drifta panel so I can see state of charge, etc. The meter was more to help me "follow the sun" with the blanket (if I ever needed to). I have battery monitors/meters on all batteries so can see the voltage. But it is an interesting and missing value over the other units on the market.

 

[Boots in Action]

Steady there @Drover . Whoa!! For @Macca_75 , Yes my Powertech PWM controller 30A (approx $185.00) cost more than the MPPT controller I have now when I bought it years ago, when MPPT was relatively new. Technology has improved and made (proper) MPPT controllers cheaper!

Morning @Drover, speaking of changing values and prices, I did a check on Ebay on the "current replacement" costs of our solar controllers - past and present.

My original Powertech 30A PWM controller now costs around $204.00 (incl postage) unless on special. Comes from an Australian distributor. Good unit!

My latest LD Tracer MPPT 30A controller is around $130.00 (free postage) (could be less on special) and comes from Australian distributor. Proper MPPT too, has its own display screen and does not need separate panel to work with phone.

Your Morning Star 35A PWM controller now costs around $220.00 (incl postage) and comes from USA.

So it is a "no brainer" as to what is the best value. MPPT by a mile with greater efficiency and heaps more features with user adjustable settings and logging ability. But then "good" PWM controllers are also much cheaper too, however do not have the features of dearer MPPT type.

I guess it is a sign of the times that the latest technology with most electronic equipment is now more reliable and getting cheaper as production increases. Also, the "throw-away" society now reigns supreme!! Take mobile phones for instance!! Cheers

 

[mikerezny]

Cheers @mikerezny - I have the Drifta panel so I can see state of charge, etc. The meter was more to help me "follow the sun" with the blanket (if I ever needed to). I have battery monitors/meters on all batteries so can see the voltage. But it is an interesting and missing value over the other units on the market.

Hi,
you have way more monitoring than I have. But I have a micro system.

My power analyser is permanently connected between the solar regulator and battery. So I can easily measure Ah in, charging current, and battery voltage which lets me determine SOC and also monitor whether the solar controller is in bulk or float charging mode.

We use so little 12V that it really isn't worth monitoring usage. Our largest consumption is the fridge fan which could use 4Ah per day if it was running continuously. There is also a small 12V fan which is used occasionally.

cheers
Mike

 

[Macca_75]

Sorry to be the bearer of bad news @Macca_75 . Running your vehicle to charge your van battery will not really do the job of fully charging it. Your battery will need approx 14+ volts to do any real good unless you have a DC to DC charger. Not knowing what sort of modern vehicle, alternator charging voltages in modern tugs is not high enough to do any good. Have a look at the attached info from Redarc and see where your tug sits as regards alternator output voltage. hang in there - at least you will know the pitfalls!!

Covered (I think). The Anderson is hooked to the cars Aux battery (so I can run "stuff" without the car running). When the car is running (depending on the state of the Aux battery) I get anything from 12v (really flat battery) to 14.4v (charged). Smart charge is disabled on the car

I know the Fridge will drain the Aux battery if we pull up for a stop and I don't disconnect it, but it's isolated from the car battery so no drama's. If we stop for fuel I am OK with this. If we stop for lunch I tend to switch to gas manually anyway. If I forget it's effectively connected to 2 x batteries now and I'll be adding another to the van soon so it will be 3 in parallel anyway. No drama's in the past 4 years so I'm good with that

From memory I think the drifta said it was adding about 10A back into the batteries when connected (but thats only my poor memory)

 

[Boots in Action]

Covered (I think). The Anderson is hooked to the cars Aux battery (so I can run "stuff" without the car running). When the car is running (depending on the state of the Aux battery) I get anything from 12v (really flat battery) to 14.4v (charged). Smart charge is disabled on the car

I know the Fridge will drain the Aux battery if we pull up for a stop and I don't disconnect it, but it's isolated from the car battery so no drama's. If we stop for fuel I am OK with this. If we stop for lunch I tend to switch to gas manually anyway. If I forget it's effectively connected to 2 x batteries now and I'll be adding another to the van soon so it will be 3 in parallel anyway. No drama's in the past 4 years so I'm good with that

From memory I think the drifta said it was adding about 10A back into the batteries when connected (but thats only my poor memory)

@Macca_75, It would appear that you have covered a few issues that cause many a new vanner problems with battery charging whilst on the move. Just a gentle reminder of how much current is drawn by 3 way fridge when running on 12 volt and when car not running. A 2 hour stop without changing to gas will rip a lot of juice out of auxiliary battery (maybe more than 50% of its capacity) which is not good for recharging and longevity of that battery. Have a safe and enjoyable trip.