Converter Draining Battery When Boondocking

Hello everyone. Been camping and always connected to power for about 4 years now. I decided it was time to do some off grid exploring. I have an 18 foot bunkhouse and since the battery was already 4 years old, I put a large tongue box and loaded in a 200ah sealed Renogy battery. Checked it out when I received it and it was at 12.6 volts. Topped it off and installed it.

All was well the first couple of weeks while connected to power. Kept an eye on it using a Grape Solar charge controller that records voltage over time and it stayed at 13.4-13.5 volts. So before the big trip, I decided to unhook from power and test it out. Float was at 13.4 and within 15 minutes, I'm hitting 12.5 volts.  Seemed odd. I isolated the battery and hooked a charger up to top it off...just in case. Charger showed 100 percent in about an hour. Reconnected to the trailer and had the same result of a quick voltage drop. All I had on was the refrigerator on propane and the propane detector. Nothing else, not even a light.

So, I isolate the battery again and top it off. Probably hit 100% in just a couple of minutes.  I then left it disconnected from the trailer and hooked a 750 watt inverter directly to the battery and put about a 100 watt draw on it. Battery wasn't even phased. Left it connected for an hour and it only dropped from 13.4 float to 13.2. That is what I was expecting.

Could it be that the converter is back feeding in some way? Not sure that is even impossible as I'm not an electrician.

I tried to find this exact scenario in the forum before posting, so I apologize if this is a exact repeat situation that has already been answered.  Any advice is appreciated. If you need more info, just let me know.

Forgot a possible important factor. My converter cooling fan use to never be on. It is on 24/7 now. No change in what I power in the trailer.

Skinny76 said:

Forgot a possible important factor. My converter cooling fan use to never be on. It is on 24/7 now. No change in what I power in the trailer.

Click to expand...

The converter is a transformer with 120v input and 12v output; it doesn't use 12v power, instead it's a source of 12v power so it doesn't seem likely that's your issue. The fact that the converter cooling fan runs continuously makes me wonder if you've got a phantom 12v draw somewhere in your system. The converter senses this draw causing the fan to operate. I would disconnect from shore power, pull all your 12v fuses then insert one at a time, watching battery draw, and see if you can find one with an unusual draw then go from there.

The drop from 13.4 to 12.5 is normal  12.5 or 12.6 is NORMAL resting voltage for a 12 volt lead acid voltage.. the float voltage is 13.5 to 13.6.  The Float bleeds off very fast when the charger is shut off.

John From Detroit said:

The drop from 13.4 to 12.5 is normal  12.5 or 12.6 is NORMAL resting voltage for a 12 volt lead acid voltage.. the float voltage is 13.5 to 13.6.  The Float bleeds off very fast when the charger is shut off.

Click to expand...

Apologies, as I reread this I see I misread some numbers. I agree with John. First you need to start with a fully charged battery which is then disconnected from all charge sources and the surface charge is allowed to dissipate so the battery reads about 12.6v. THEN do your load testing and see if there's a problem. Any voltage above about 12.6v is leftover surface charge, so any drawdown numbers from float voltage to about 12.6 are meaningless.

Some of the numbers you stated don't make sense if the battery is truly isolated from charging sources (solar or shore).  The battery cannot sustain more than 12.6v without shore or solar power present to add to its charge.  The normal voltage for a fully charged 12v battery is 12.6v.  Anything more is either active charging or the residual (aka "surface charge") from active charging.  As soon as any power draw is applied, a surface charge will disappear and the voltage drops.

The converter is a 12v source, converting 120v power to 12v and the fan operates when the internal temperature from the conversion gets high.  The converter is not involved when drawing power from the battery and the fan doesn't run.  If your fan is on, the converter must have 120v power from somewhere.  Please identify the brand and model of your converter so we can better determine its functions.

The converter model is WF-8375-P. The fan is running non-stop when connected to shore power.

I'm going to try the suggestion to disconnect from shore power, pull all the 12v fuses and see which port is pulling the battery down. Start the process of elimination.

Some of your information is confusing.

"So, I isolate the battery again and top it off. Probably hit 100% in just a couple of minutes.  I then left it disconnected from the trailer and hooked a 750 watt inverter directly to the battery and put about a 100 watt draw on it. Battery wasn't even phased. Left it connected for an hour and it only dropped from 13.4 float to 13.2. That is what I was expecting"

It is not clear what exactly you did here. If the battery is disconnected from the trailer and you connect an 750 watt inverter with a draw of 100 watts for an hour you could not at any point maintained a voltage of 13 volts. You will need to clarify what you did in order to get reliable help.

My other observation is that it is very likely your new battery is good as your voltage readings indicate.

You said you mounted a large tongue box for the new battery. Did you remove the old battery or is it still being used ?

 

The converter model is WF-8375-P. The fan is running non-stop when connected to shore power.

Click to expand...

That is within the range of "normal", depending on battery condition and amp load on the 12v system.  Since shore power is present, it has nothing to do with the battery. The converter is supplying all 12v needs and also charging the battery is needed.
Sorry, but I have to nitpick again. To the best of my knowledge, there is no WFCO 8375 model - their model numbers are 85xx, 87xx and 89xx.  Could digits have been transposed?  There is a WF 8735-P model. Looks like this:  https://wfcoelectronics.com/product/wf-8735-35-amp/

Do please disconnect from shore power and also solar panel (if you have one), then measure the battery voltage when fully charged and then again after some period of load. So far I haven't seen any numbers that reliably indicate there is some excessive discharge going on.

I think I figured it out. My solar charge controller is reporting much lower volts than my ship to shore charger and my inverter. Right now, the battery disconnected is 12.8 on per my ship to shore charger and 12.8 per my inverter. Solar controller reports 12.5 volts and a 58% remaining battery. I think the solar charge controller is screwed up which is what I was using to determine the battery drain.

One more observation. It is not the solar charge controller. It is the blutooth app that is the problem. It does not refresh unless you close and reopen the app. That may explain why is showed the 13+ volt reading I mentioned earlier. Once is lost a connection, it never refreshed, so it only showed the charge immediately after removing shore power.  I just closed it and reopened. It now shows 12.7 volts and 100%.

I guess everything is fine except the Grape Solar blutooth app.

It is always best to use a good multimeter when problems like this arise. If you do not have a multimeter I would strongly recommend buying one. Relying solely on hard wired electronics or apps for troubleshooting is not a good idea.

Agreed.

Being able to monitor battery current will tell you a lot about why your charge might be disappearing.  Will make the fuse pulling test a lot easier than going around and seeing what might still be working or not.

Mark B.
Albuquerque, NM

I have not bought a meter just yet but I thought this may be interesting. I unplugged from shore power, cut all breakers and pulled all fuses. I already had the battery disconnected and was watching it sit right at 12.7 volts using the grape charge controller (not the app) and an inverter with no load. Both agreed at 12.7 volts. I connected back to the trailer and their is something drawing power even after all breakers flipped and not a single fuse in place.

I wont be back in a couple of weeks, but I'm going to look at the wiring to the converter when I return.

"To the best of my knowledge, there is no WFCO 8375 model - their model numbers are 85xx, 87xx and 89xx.  Could digits have been transposed?  There is a WF 8735-P model. Looks like this:  https://wfcoelectronics.com/product/wf-8735-35-amp/

Gary,

You were correct. I transposed the model number incorrectly. It is the 8735-P.

Welcome to the Forum!

Lots of good information here.  One thing I noticed - you have said CONverter some places and INVerter other places.  A CONverter takes 120VAC and converts it to 12VDC to charge the battery and run 12VDC stuff.  An INVerter takes 12VDC from the battery and INVERTS it to 120VAC to run 120V stuff off grid.

Do you have both?  If so, you need to turn the CONverter off when boon docking.  Otherwise you draw 12 V, invert to 120V, and then convert back to 12V to charge the battery.  This is a power consuming loop which needs to be broken.

Check your break away switch. It can draw power with all your fuses removed

That was it!!!! Break away switch was the culprit. Just got back to the trailer today and checked it. It had been pulled loose. Clicked it back in and re-tested..... no draw. Thanks everyone for your help. I'm ready to hit the road now!

Thanks for the feed back.

Now go and enjoy.