Hi all, I wish to run an anderson plug from the coupling area to the battery (fused) - does this need to go via the fuse box/BMS or direct to the battery etc .. ?? Just want to charge battery from the tug. Thanks DOS
Hi @dosmos , If you already have connections to your BMS (Setec or later type), then one of the wires from tug battery/alternator will be connected through the BMS. Unfortunately, the BMS has power diode in line to prevent any current from van battery being drawn when the high tug starter current is required. The connecting wiring is insufficient to carry such current, especially if tug battery is low and van battery is considerably higher. The power diode whilst protecting the connecting wiring will cause approx 0.7 volt drop in addition to other losses in transferring voltage/current from tug to van, losses which will prevent your van battery from receiving sufficient voltage to achieve a proper charge. Using a separate heavy cable with connections by Anderson plugs will reduce this loss but still needs to be isolated from the tug alternator when engine not running and also when wanting to start tug. A separate relay or better still, a VSR (voltage sensitive relay) will do this for you. But even then, if your tug has a "smart alternator", see attached, you will not see much joy. The only real way to achieve a proper charging current transferring from tug to van battery is with a DC to DC relay. This device takes any voltage from tug alternator and boosts this output to a usable charging voltage at the van battery. Eg, tug alternator/battery voltage IN to van wiring at say 12.6 volts is boosted to say 14.6 volts OUT to charge van battery. These settings are user adjustable.Hi all, I wish to run an anderson plug from the coupling area to the battery (fused) - does this need to go via the fuse box/BMS or direct to the battery etc .. ?? Just want to charge battery from the tug. Thanks DOS
Hi,Hi @dosmos , If you already have connections to your BMS (Setec or later type), then one of the wires from tug battery/alternator will be connected through the BMS. Unfortunately, the BMS has power diode in line to prevent any current from van battery being drawn when the high tug starter current is required. The connecting wiring is insufficient to carry such current, especially if tug battery is low and van battery is considerably higher. The power diode whilst protecting the connecting wiring will cause approx 0.7 volt drop in addition to other losses in transferring voltage/current from tug to van, losses which will prevent your van battery from receiving sufficient voltage to achieve a proper charge. Using a separate heavy cable with connections by Anderson plugs will reduce this loss but still needs to be isolated from the tug alternator when engine not running and also when wanting to start tug. A separate relay or better still, a VSR (voltage sensitive relay) will do this for you. But even then, if your tug has a "smart alternator", see attached, you will not see much joy. The only real way to achieve a proper charging current transferring from tug to van battery is with a DC to DC relay. This device takes any voltage from tug alternator and boosts this output to a usable charging voltage at the van battery. Eg, tug alternator/battery voltage IN to van wiring at say 12.6 volts is boosted to say 14.6 volts OUT to charge van battery. These settings are user adjustable.
I have attached several pieces for you to consider when trying to overcome this problem.
Thanks for the update @mikerezny . These things are changing all the time and one needs to check before making any "rash" statements. It is good that there is now a relay incorporated into the later model BMS to prevent any power being taken by starting currents from van battery, and now no loss of charging voltage/current with a diode.Hi,
your statements concerning a diode in series with the AUX input relate ONLY to the Setec BMS.
The BmPro J35 does NOT have a diode in series with the AUX feed.
Here is an excerpt from the J35 BmPro manual:
AUX INPUT (AUXILIARY)
The power supply input terminal “AUX INPUT” provides an alternative option for powering the loads and charging the caravan battery when mains voltage is not present. This input is powered from a suitable +12 V system (e.g. your vehicle). The voltage of this external DC power source must not exceed 14.8V.
This input is isolated using an internal relay, so it is strictly an input. J35 will never supply current to anything connected to this terminal.
Take care
Mike
@mikerezny, I think you have explained the situation perfectly , and unfortunately for @dosmos, he hopefully can see there is no easy answer, except to spend more cash, which may be for little return, if solar charging is a better bet. The only problem is that solar charging is not possible at night or semi-darkness, and still limited when travelling.Hi @Boots in Action,
as far as I am aware, most BMS for vans have only the most simplistic facility for charging the van battery from the tug alternator.
Usually achieved by connecting the tug output to the van battery via a relay or a isolation diode. In both cases, the charging voltage is determined solely by the alternator voltage.
There are two explanations for this.
1: The better way would be to incorporate a DC-DC convertor into the BMS and thus remove the dependence of the van battery charging voltage and current on the tug alternator voltage. This would have been beyond the capabilities of early van BMS. And is probably outside the price range of the later BMS. Hence, why it has not been done.
2: I suspect that BmPro and Setec have also noticed with the increasing availability of solar there is no way less dependence on needing the tug alternator to charge the van battery. Hence, complex solutions to charge the van battery from the tug are not required. Especially in those cases where most camping is done on powered sites. Further, it makes economic and environmental sense to charge the van battery from rooftop solar panels if fitted rather than burn extra fuel to charge the van battery.
I do have 12V from the tug going into the Setec ST20 series III, but it is really not necessary, more just for completeness.
Our Falcon alternator usually runs at about 14.6V, which means 13.9V to the van battery allowing for 0.7V drop across the Setec isolation diode.
So, this just keeps the van battery on float and with such a small current drain it is not chewing that much more fuel. Especially in comparison to the 15A drawn by the three-way van fridge.
Here is one trick I do when camping in one place for an extended time. In the early days, I flattened the car battery when we stayed in one spot for 7 days with no driving. All the door opening, leaving the boot opened etc chewed a lot of power from all the interior lights. Solved that problem by getting into the car setups to turn off all internal lights.
But, I worried a little about having a flat battery, so I usually solar charge the car battery once or twice every 7 days.
Then I realised that if I left the van connected to the tug, charging the car battery would also charge the van battery. At the very least, it would supply enough power to supply any devices used in the van. So now, I leave the solar panel connected to the car battery quite often and thus keep both the car and van battery charged at the same time. Then connect the solar just to the van battery on some days to bulk charge it separately.
Probably a lot of overkill. But, when camping, there are a lot of brain cycles spare, so best to apply them to something useful.
take care
Mike
Hi,
one other solution which might work especially if one already has a good 240V multi-stage battery charger.
Run a good sized connection from the tug battery up to near the van battery. Install a 240V inverter capable of supplying the battery charger.
Then use the inverter to power the 240V battery charger.
This would be a great solution if one already has a good battery charger and an adequate inverter.
In effect that mimics a DC - DC charger. Well, actually, I should patent the idea as a DC-AC-DC charger.
take care
Mike
Hi,Lol,lol,lol,lol,,................................... bit more than .7v loss in that set up...........................
Interested to see how that turns out. The mod I did with that small dc dc board is working pretty well for me - I added a small cooling fan that is powered from the output (setec aux input side) and now I can hear what the unit is doing based on fan noise/speed. It fires up when the ute altenator is producing enough volts and/or the solar on the ute has charged the 2nd battery (so gives surplus to caravan) which is exactly what I hoped forOver the Christmas/New Year period, I still intend to remove my Setec ST20 Series III and look at replacing the power diode with a lower loss Schottky type. I will let you and @jazzeddie1234 know the results and if it is possible without too much problem.
Hi @dosmos , just because we gave you indigestion with our answers (sorry), does not mean it cannot be achieved. You will have to investigate the priority it has and the depth of your wallet to get around these things. Good luck and Merry Christmas.Thanks all for the advice - food for thought !!