I have a auto battery charger wired into the array. The 2-amp camper charger is just not enough to charge a battery, so I have a 10 amp hooked in. My question, does current flow backwards through the DC side of the transformer and drain power?When I turn the charger off I assume all it does it disconnect power to the AC side of the transformer.If you know I would like to hear, if you don't then you don't so no comment needed.

Power does not flow backward into the charger.

can you also elaborate? just for curiosity. What stops it?

Best to measure or check with the manufacturer.Generally it would be very low as a few milliamps max unless it had some special control system electronics to run.Might help to post exact model numbers.What is the concern? The 10 amp should not materially affect the 2 amp from maintaining the battery. Although typical RV idles at 1/4 amp to 2+ amps so best to be disconnected with a small maintainer.

Diodes/rectifiers allow current to only flow in one direction. So current will not flow into charger.

marininn wrote:can you also elaborate? just for curiosity. What stops it?In simple terms, they have a diode or switching transistor that only allows D.C. Current to flow one direction.

batter charger drain? | Good Sam Community

18 Replies

westend
Explorer
Dec 23, 2016
Buy one of these High amperage diodes, install it on a battery terminal, and fret no more.
Gjac
Explorer III
Dec 23, 2016
It really depends on the maintenance charger you have. I bought a cheap one from HF and it will drain your battery if the power goes out.
Mandalay_Parr
Explorer
Dec 22, 2016
marininn wrote:
OK, then. I will leave my charger attached to the battery, sounds like no flow, or should I put a switch on the 12V+ wire from the charger?

No switch.
Jerry Parr
marininn
Explorer
Dec 22, 2016
OK, then. I will leave my charger attached to the battery, sounds like no flow, or should I put a switch on the 12V+ wire from the charger?
ScottG
Nomad
Dec 22, 2016
marininn wrote:
The charger in question is a very old Sears unit, possibly from the 60's.
I understand if it has diodes.
My understanding is these transformers basically have two windings. The one on the AC side about ten times more windings than the DC side and the DC side a heavier gauge. I do not know much more than that other than a diode would stop reverse flow…
Time2troll, umm, just , umm

That is how a very basic charger is built and if it weren't for the diodes the battery would indeed discharge through the secondary windings of the xfmr.
RoyB
Explorer II
Dec 22, 2016
I actually have two converter/chargers wired in parallel on my setup and I can use either the WF-8945 or PD9260C Charger unit by just turning on the charger that I want to be using. When I upgraded the Charger unit to a higher DC AMPs model I left the original 45AMP unit in its location in the bottom compartment of the Conevrter and then mounted the higher DC AMP model stand-alone closer to the battery bank. I have accidently left both on at the same time and didn't trip any breakers but I normally just have one on at a time...

Having them paralleled has not been a problem for me. Gives me a backup Charger unit... They are always connected and I turn on the 120VAC Circuit breaker to the one I want to use... Only the DC OUTPUT leads are paralleled...

Roy's image

My PD9260C has the dual DC terminals that gave me the idea to do this...

Google Image

If there is a DC load doing this it must be a very small minimal drain...

Roy Ken
2112
Explorer II
Dec 22, 2016
I have an old Schumacher that I measured the resistance at the output clamps while unplugged and unpowered. Red to red lead measures 920K ohms. Reverse polarity (red to black) and it measured 22K ohms. This indicates there will be a VERY small drain on mine. YMMV, measure yours.
landyacht318
Explorer
Dec 22, 2016
I'd test it, first with my clamp meter, and if that read 0.00, I would use my regular digital multimeter set to DC amps, inline.

No sense guessing.
marininn
Explorer
Dec 22, 2016
The charger in question is a very old Sears unit, possibly from the 60's.
I understand if it has diodes.
My understanding is these transformers basically have two windings. The one on the AC side about ten times more windings than the DC side and the DC side a heavier gauge. I do not know much more than that other than a diode would stop reverse flow…
Time2troll, umm, just , umm
The_real_wild1
Explorer
Dec 22, 2016
RCMAN46 wrote:
If it is a smart charger such as the Battery Tender it will discharge the battery if AC is removed.

The smart chargers monitor the battery voltage with a small load on the battery.

I had one run my battery completely down in a couple months due to a GFI outlet tripping.

Are you sure the battery didn't just drain down in a couple months by itself? I don't think the charger will draw on the battery unless plugged in. The only way to know for sure is to use am amp clamp. Check draw with it plugged in vs not plugged in. If I remember to bring mine home from work I could check and verify this.