Help troubleshooting my 12v system please

[Johnboyy]

I have a camper build thread over here: https://expeditionportal.com/forum/threads/nissan-primastar-camper-build.223043/

Built 2 years, up until now I have been running off the starter battery plus solar, my loads are small and I'm not normally not driving for long.

However I will be travelling more this summer and want to step up to a dual battery setup as the weather will be hotter, I'll need the fan running all night and will want to run the cooler more too. I had most of the provisions in place from the start, just needed a place for the second battery and to hook it up.

Finally did that last weekend and it hasnt gone as expected.

This is the setup (there are fuses, just not shown in the diagram)

I don't have high end needs so it's just two regular lead acids, voltage sensing relay, solar panel and PWM controller. The Solar and PWM have been working just fine up until now connected to the starter battery.



The problem is that I'm running down the starter battery. I was parked up all week and went to start it yesterday and it wouldnt go. Stupidly I didnt measure voltages as I needed the van running so I put it on charge for an hour and it was fine. But the voltage wasnt too low as it was turning over, just not fast enough to fire.


I have a few weeks before we go on our road trip, what should I be doing now to troubleshoot/resolve it I'm not keen on throwing money at the problem just yet as I have 5 weeks to go, would rather understand it first. I'm going to start by putting voltmeters on both batterys for easy checking, plus an indicator light for the VSR that's not hidden out of sight like the unit is. Anything else I should do to understand the problem?

 

[NatersXJ6]

Is the VSR adjustable? Possible that you just have it set to open too low? Various vehicles have different needs to crank properly, and a weak (or even new) battery with a relay opening too low might not crank you over enough. You could be diagnosing a combination of electrical system and tired engine/ignition/starter as one issue instead of many.

As an anecdote, but similarly, my JK can be drawn down by the fridge unless I set the voltage cutoff to its highest level, and even though there is enough to maintain a measurable voltage at the battery, it won’t start.

 

[Johnboyy]

But why would the voltage be dropping is what's confusing me, there's nothing switched on, and nothing else has changed so I don't know what would be causing it. I wasn't flattening the starter battery before now. I've hooked up two meters so going to keep an eye on everything for a few days

Vsr is fixed, 13.3 connect. 12.8 disconnect

 

[Joe917]

Probably unrelated to your issue, but I would rather see your loads coming off the house battery (through a fuse block).

 

[Johnboyy]

It's the way the controller wanted to be wired and it's worked fine up to now. I've fat wiring back to the battery.

No shortage of fuses either, I was just too lazy to draw them.

Had to move it today but won't need to move it for a few days now. I've rigged up a pair of meters. Batteries were at 13.9 an hour after running. Dropped to 13.4 an hour later and are still there currently (parked in the shade so not much solar today) VSR is still connected at the moment.

Gonna monitor the voltages over the next few days and see where they go.

 

[NatersXJ6]

My next step would be to disconnect both batteries and check their voltages separately, check the water in them, and then charge them individually, disconnected, with a plug-in charger to see if there is a problem.

After that, reconnect each battery to its respective system without the relay, and see if it draws down.
Then start thinking about your connecting relay again.

You can probably trace a little more detain if you have an amp meter that you can log data with (spendy) or even just watch for draw while it sits.

 

[NatersXJ6]

Maybe also tell us what solar panel size you have and what its charging voltage is? You might just be cooking off your water and coincidentally noticed a fried battery at the same time you made a change?

 

[jonyjoe101]

On my van I have a 300ma drain on the start battery, after 2 days the battery won't crank over. I have to keep topping it off from the house battery 24/7. I couldnt find where the drain is coming from, from looking at the internet the max drain allowable on the start battery is 30ma.
One thing I would look at is to check what is the max voltage reached while charging with solar. You should be getting 14.4 volts at the battery terminals. I encountered voltage drop on every controller pwm or mppt that I use.
On my ecoworthy mppt I had to set the bulk setting to 15.5 volts just to reach 14.6 volts on the battery terminals of my lifepo4. Anything less and the battery wouldnt fully charge. If you have voltage drop your batteries are probably not getting fully charge. You have to have 14.4 volts at the battery terminals for several hours.

This is a picture of my start battery with a dc ampmeter showing the drain. Everything in the van was off. I suspect the drain is from the radio but havent checked it. I read many reports of the radio even when its off using alot of power for the clock/memory. Since I had my dc to dc charger connected to start battey havent had any more no start problems. The start agm battery I'm using is over 10 years old but still working like a champ.

 

[Johnboyy]

Well that didnt take long! went out this morning and the VSR is disconnected and the house is at 13.9 and the starter is down to 12.5.

I've switched off the solar to see what the house battery does over the course of the day. The batteries are sealed so I don't think I can check for levels, but I can disconnect them, charge independantly and test.

Can also easily remove the VSR and test with a plain wire linking them.

have a 175W solar panel, would have to check the settings on the charge controller but 99% sure float voltage is set to 13.9

https://archive.goughlui.com/wp-content/uploads/2020/05/2020052611537043.jpg

@NatersXJ6 you make an interesting point about cooking the battery. Maybe the starter battery has been on the way out for a long time, but the solar was keeping it topped up every day so I never noticed.


I'll monitor the voltages for another day or two and see what happens. I'm wondering if I'm on a hiding to nothing though with two old batteries and should I start with two new identical ones.

 

[Johnboyy]

starter 12.4, house 12.8

 

[NatersXJ6]

Are your batteries the same? Swap house and starter positions. I would be willing to bet the fault follows the battery.

If that starter battery is more than a couple of years old, I would replace it. Normally I’m all about cheap troubleshooting first, but you will never know 100% if you don’t start with a known good condition. If I’m thinking of the right thing, I believe those “sealed” or “maintenance free” lead acid batteries will still lose water vapor if hot or overcharged. I would guess that a PWM charger on a starter battery is going to do some occasional overcharging with 175 watts of solar behind it.

 

[shays4me]

From the reported voltages it sounds like your batteries are properly isolated now. If the voltage sensing relay is working that way every time I'd look for a draw on the starter battery side or maybe your starter battery is showing it's age and dying. If the starter battery goes dead and your house battery stays charged then it's definitely not related to your house battery wiring. As for the current voltage readings, they're both fine.

 

[Johnboyy]

I believe those “sealed” or “maintenance free” lead acid batteries will still lose water vapor if hot or overcharged. I would guess that a PWM charger on a starter battery is going to do some occasional overcharging with 175 watts of solar behind it.

So am I just going to cook any new batteries too?

MPPT controllers seem to have become a bit cheaper than a few years ago (about the only thing that has)

Would an MPPT be less likely to cook the new battery? This seems very reasonably priced https://eu.renogy.com/renogy-rover-20-amp-mppt-solar-charge-controller/

 

[Johnboyy]

Thanks for the advice btw. Also discovered at lunchtime that my clamp meter no longer reads DC current, which is real unhelpful right now.

 

[Johnboyy]

Starter 12.1, house 12.8

Have disconnected the VSR in case it's drawing more than it should