Aux battery charging issues

[DiploStrat]

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Having done a little more research on the setup, I now think the problem is at least in part due to the mismatch in main and aux batteries. Main is a 70ah lead acid, aux I have recently upgraded to a 110ah AGM.

What I think may be happening is that the alternator is thinking the battery system is fully charged, and not providing more power. Hence the aux battery is never bring fully recharged as it is only trickling charge at best.

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You could not have a bigger mismatch than I did, 150Ah of starter and 600Ah of camper battery. As long as the batteries are grossly of the same type, e.g. lead acid, and only combined when under charge, size doesn't matter.

You can have the my-starter-battery-is-charged-so-my-camper-battery-won't-charge, but it happens when the wire between the two batteries is too small. To be sure, as long as the voltage of one battery is higher than that of the other, it WILL charge the battery with the lower voltage; it will just do it very slowly.

Above and beyond questions of the National Luna malfunctioning, the next question is the the size/length of your wiring. It doesn't matter if you use a manual switch, a relay, an intelligent relay, or a battery to battery charger, if the wiring is too small, the performance will be poor.

You seem to be thrashing a bit, this may help: https://cookfb.files.wordpress.com/2016/09/dual-battery-slides-2016.pdf

Some of your comments indicate that you might benefit from reading this: https://cookfb.files.wordpress.com/2016/09/battery-charge-slides.pdf

These, and their companion pieces are on my website under "Documents." You may find them useful.

 

[dreadlocks]

the next question is the the size/length of your wiring

x2, sounds like his aux battery is being limited by the wiring to just a couple amps.. my trailer can only get like 3-4A off the plug wiring and it takes forever to fully charge via alternator.

 

[john61ct]

Blue Sea Circuit Wizard app good for sizing

And connections go bad too, get a pro to check for resistance, show you how while he's at it.

 

[ColMonty]

thanks fellas, I appreciate the advice - as always.

I spoke with the UK NL rep's electrical guy this morning. Whilst it didn't reveal a whole lot, at least I did get him to explain in baby steps how I would go about installing an isolating switch.

The battery was thankfully fully charged this morning, and I dropped it off this afternoon at the port for it to be shipped to Egypt. Obviously I disconnected everything which may draw a current.

I will see what I can find in Egypt for a high-current isolating switch. I think anything else is beyond me at the moment.

DiploStrat, thanks for the PDF links, I'll have a look tomorrow whilst someone else is driving - trains, planes and automobiles. Oh, and 600ah?! I had to custom fit my 110ah into the engine compartment. I think it would be 4.2L of engine OR the 600ah battery!

Thanks again all.

 

[Perfect Switch]

Describe how is the auxiliary battery grounded.

 

[ColMonty]

I'll have to get back to you in a few days - the truck is currently being shipped to Egypt so I won't have access to it for maybe 10 days.

What should I be looking for? I.e. what do you feel may be the/an issue? That it's grounded to a body panel poorly, or that the panel may not have a good contact with the chassis? Or something else?

Thanks

 

[dreadlocks]

redundancy is a good thing, put another grounding strap on it.. have it attach to a different location on the chassis.. worst case it dont help at all but now you have redundancy so likely hood of having a grounding issue in future are very tiny.

its gotta be attached to unpainted metal where you attach at, find a raw steel bolt going into a frame if you can for best results.

 

[DaveInDenver]

redundancy is a good thing, put another grounding strap on it.. have it attach to a different location on the chassis.. worst case it dont help at all but now you have redundancy so likely hood of having a grounding issue in future are very tiny.

Grounds are the most important and usually the worst thought about part with multiple batteries. You have either 2 or 3 grounding systems on RV vehicles with multiple batteries: the chassis ground, the house ground and if the house will be charged with an engine-driven alternator the interconnecting ground.

Just randomly adding cables might solve one problem but create new ones. So it really needs to be done correctly so you don't inadvertently mask an issue or create a latent issue, loop or sneak path. If the system worked correctly at some time then a conductor needs to be replaced, not augmented. If it's never worked right then there may be a missing or insufficient cable.

 

[Perfect Switch]

Run a heavy gauge cable from the negative post of the main battery to the negative post of the auxiliary battery. Then, if you want to be a rockstar, run a heavy gauge ground cable from the casing of the alternator to the ground post of one of the batteries. This will insure proper and efficient grounding, assuming your cabling and terminations are good. If you're using a voltage sensing relay, make sure its ground is bonded to battery negative and its positive connections are low resistance. If these changes don't resolve the charging imbalance issue, think about getting a better isolator if your relay is not opening, closing, or passing current properly.

 

[ColMonty]

So I finally got a response from National Luna today, after I emailed them again, so I'll give a quick update.

I managed to find a battery isolator switch in Cairo and fit it myself. It's wired to the battery terminals on the NL Intelligent Solenoid. It works as it should, every time. It's just a ball-ache to have to switch it all the time.

This left me pretty sure the problem lay with the solenoid, which NL agreed with. They suggested finding and fitting a new/different solenoid and gave some specs which I'll paste below. I asked if a solid-state relay would do the same job and he confirmed it would.

Now, someone kindly suggested a Blue Sea relay, I think? But if I remember correctly that has charging sensors in it, so my question is: should I be avoiding such relays given I am intending to keep all the NL electronics? Or is any relay going to work, regardless of any additional features?

So now I just have to find a solenoid/relay in Ethiopia/Kenya/Uganda/Rwanda/Burundi/...

----------- excerpts from NL emails --------------
The solenoid we use is a Cole Hersee brand but there are a few low-cost equivalents available that will work.

Unfortunately we have no distributors or service agents in the majority of Africa until Namibia but you might be able to find a solenoid from an auto-electrician or 4x4 fitment centre.

(They are often used for winch systems ).
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The solenoid coil must have a 12V rating. The current rating should be 80A or more. The one we use has a continuous rating of 85A with make / break peak rating of 400A.

A large relay or contactor with high DC current rating will also work.
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[luthj]

Some solenoids can be disassembled to service. If yours can, then pull it apart and check the contacts. They may just need cleaned up, and the slide mechanism lubricated.

 

[rayra]

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If my thinking is correct then I think I need some form of BCDC inline charger, such as made by Redarc or CTEK. However, I'm shipping my truck from Italy to Egypt in the morning so I'm keen on simple solutions.

Interestingly, I think regardless of which relay or solenoid system is used, this scenario would still play out, no?
...

This is where things start getting ridiculous / ridiculously expensive. You have one 'smart' gadget already interfering and you want to layer on another.
It's apparent the NL is preventing your vehicle's dumb charging system from seeing the load / sink of the Aux, because the NL is 'managing' the Aux. And the NL apparently isn't managing it correctly. It's failing to pass through the available power when your vehicle ('s charging system) is running. It is effectively doing the very opposite of what you bought it for. I'd get it replaced or bypass it.

The dumb 200A solenoid in my setup isn't managing anything. I start the car, it opens (closes, really) and my charging system 'sees' both my starter and aux batts as one draw / sink. And when my key is off the solenoid isolates my Aux / 'house' consumption. My solenoid isn't 'managing' anything.

I'm not trying to make a virtue out of being Cheap / 'poor', but my setup isn't having the problem yours is. If I was heading off into the bush I'd want as simple a system as possible. Much less to go wrong, as you are (re-)discovering. But in these days of internet and express shipping it's not a critical issue. Just an expensive one.
I'd suggest taking a metaphorical step back from the problem and looking at the whole issue. What are you trying to solve / provide? What gets you there. What's critical and what's 'nice to have'. And what is a waste of effort. And at a minimum - once I've verified everything is as correctly connected as you can manage - I'd be pressing for a NL replacement.

Too, as part of troubleshooting, I'd be swapping my batteries in the arrangement. Just to watch the NL magically work correctly once the smaller battery / sink is on the 'Aux' side of the thing. I strongly suspect that's where the engineering design flaw lay.


as an aside, since I wanted to eventually be powering a large winch, I chose to go with a solenoid / simple combiner setup and I specifically chose to go with matching capacity batteries as that's a much mor eimportant issue on discharge. They are in fact two of the same brand / model. Interchangeable. And also deliberately SLA for both affordability but also because I can readily get a relatively inexpensive replacement just about anywhere.

 

[dwh]

There's a long thread here about NL's crapping out. Mostly due to heat as I recall. The Blue Sea ACR...never seen a reported failure.

 

[ColMonty]

Thanks guys. @rayra all great points, I'm totally with you. I have already put a manual isolator switch in so I'm totally out of the woods - just tired of switching it. Also, it is the dumb solenoid part which is broken in my case.