Another way to charge a battery?
Submitted: Thursday, Jun 02, 2011 at 09:17
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Member - Kevin S (QLD)
A question to folk who understand 12V power.
My tow vehicle (Jackeroo) has an Anderson plug which is a dedicated power supply to my 3 way fridge when I am towing the van but when not towing it is surplus to requirements. Can I safely use it to charge an auxiliary battery by bringing a lead from the Anderson plug under the back doors to a battery secured in the luggage compartment. A deep cycle AGM battery.
Thanks.
Kevin
Reply By: Member - Boobook - Thursday, Jun 02, 2011 at 10:01
Thursday, Jun 02, 2011 at 10:01
Kevin, the answer is "definitely maybe".
It all depends on how it was set up.
There are 2 main ways that your set up could work.
a)You have one of those motion switches and the Anderson is hard wired to your main battery. In this case it will charge the aux but will also discharge both batteries. They will effectively be in parallel.
b)It is wired up so the Anderson plug is only powered up when the ignition is on. This will isolate the batteryies when you are stopped and it will charge the battery when the vehicle is running. ( or more accurately when the accessories / ignition switch is on, depending on who wired it).
In both cases, and in particular the second one, there is probably a 20A fuse in the circuit. This would blow at times if your aux battery is very low. You could make it higher, eg 40A plus, IF YOUR CABLING and RELAYS CAN HANDLE IT. If it was installed proiperly the wiring should be ok because it should be thick enough to keep voltage drops to a minimum, but a proper installion by an auto elec is very rare indeed. Also make sure you relay in b) is 50 amp plus.
AnswerID:
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Follow Up By: Member - Kevin S (QLD) - Thursday, Jun 02, 2011 at 10:33
Thursday, Jun 02, 2011 at 10:33
Thanks Beebook. It is b). There is a motion switch in the van. I have tested the plug on the Jack with ignition off and there is full voltage there. Heavy wire and the fridge in van now works really
well with adequate power supply so there should be enough to charge a battery. Installation was done by caravan refrigeration specialist.
Kevin
FollowupID:
729126
Follow Up By: Member - John and Val - Thursday, Jun 02, 2011 at 11:50
Thursday, Jun 02, 2011 at 11:50
Kevin,
I agree with Boobook. BUT, if you have 12V on that connector with the ignition switched off, then I believe that you actually have Boobook's a), not b).
As he says, if you connect a battery to the anderson plug it will be permanently in parallel with the cranking battery and the two batteries will go up and down together. (There are the usual limitations on charging the auxiliary battery this way, but if the chemistry is similar to that of the cranking battery you should be able to push it up to 80 or 90% full.)
You actually need some switching to allow the batteries to be connected to each other only after the engine is running (or at least the ignition is on). Otherwise fuses will blow when starting the engine or when the aux battery is low and starts charging. Suggest that you will need a relay operated by the ignition (or better the accessory voltage) in the line coming from the cranking battery. This shouldn't affect usual operation of the fridge, as it will be turned off anyway when the vehicle stops. The cheapest way is probably a heavy duty headlight relay.
HTH
John | J and V
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Follow Up By: Member - Kevin S (QLD) - Thursday, Jun 02, 2011 at 12:38
Thursday, Jun 02, 2011 at 12:38
Yes. You are right
John. I understood what he was saying but put b instead of a in my response. I am starting to learn that going off road is for wealthy people and electricians. I was looking for an inexpensive solution but there doesn't seem to be one. People keep talking about relays. I thought that was something that they ran at the Olympic Games.
I am not confident to do electrical wiring so it will mean an auto electrician and a dual battery system by the sound of it. I think I will leave the Waeco at
home and take an ice box. Can you buy ice at
Marree?
But thanks for your input
John. I appreciate it.
Kevin
FollowupID:
729139
Reply By: Member - Noldi (WA) - Thursday, Jun 02, 2011 at 10:17
Thursday, Jun 02, 2011 at 10:17
Hi Kev, Yes, I have done just this to both my 93 and 2001 Jacks. Don't forget to fit a fuse at either end, (if its connected to an Aux battery you have power available from either end) I also used a BRS big red switch (can't remember the name of them) to manually isolate the batteries, my preference after 2 failures within the club of electronic dual battery systems,
well know brands as
well.
Mind you, every one says you'll forget to isolate them and be stranded. in nearly 6 years its not happened.
AnswerID:
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Follow Up By: Member - Kevin S (QLD) - Thursday, Jun 02, 2011 at 10:39
Thursday, Jun 02, 2011 at 10:39
Ian and Paula. Thanks. I knew about a fuse at the auxiliary battery end but where does the other one go? At the plug into the existing Anderson plug or right back at the cranking battery?
And since I will need to plug the Waeco into the battery to keep it working overnight I deserve to get stuck with flat batteries if I am so dumb that I forget to unplug the charging line.
Kevin
FollowupID:
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Follow Up By: Member - Noldi (WA) - Thursday, Jun 02, 2011 at 10:47
Thursday, Jun 02, 2011 at 10:47
Yep as close to the battery as possible (I would guess but also
check that this was done when installed). I used to unplug
mine to start with found them a bit stiff and was worried I might actually put the cable out of the Anderson plug so installed the BRS.
The fuses are simply to isolate the batteries incase a short to earth develops in the cable, no good isolating just one. I learnt the hard way with a fire in a HQ pannel van many years ago ;-(
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