Aux battery charging issues

[ColMonty]

Hi,

After replacing a dead aux battery with a larger unit which is AGM, after a few weeks I'm not seeing much charge hitting my aux battery. This concerns me greatly as I am en route to Cape Town from London, currently in Italy.

Starter/main battery: old (unsure of age) lead acid 70ah
Aux battery: new Victron 110ah
Charging system: National Luna complete system

The starter battery charges as expected, consistently, and shows 12.6v after a night of inactivity. As soon as I start the engine, the voltage hits the roof, as expected.

The aux battery most often doesn't get above 11.8v. After upgrading this battery to the AGM unit it initially would charge as expected, without issue. This past few days, however, since hitting the road, it rarely seems to charge. Sometimes, a minute or so after the engine/alternator turns off, the voltage will jump to an acceptable 13v or so. I guess this is when the solenoid disengages? It seems odd, though, as I would expect the voltage to reach the top (14.2v on the NL monitor) after 5 mins of the engine running, showing that the solenoid has engaged and connected the batteries. That mini boost to the voltage doesn't last very long, though - like an hour before it is down at 11.8 - 12v.

I have been plugging the fridge into the mains the past couple of days, when available, expecting to see the voltage jump once I removed the drain - but it doesn't shift. Last night I disconnected the aux battery completely and tested with a meter - showed exactly the same as the NL and no change from when it was connected, indicating very little drain from the fridge.

So what do you think is going on? It is quite hot here in Italy right now, though I'm expecting much hotter in Africa...

Is the starter to aux mismatch a problem? Long term I think it could be, but I wouldn't expect it to manifest itself like this and so quickly.

So far the aux battery hasn't gone below 11.6v, indicating that it is receiving some charge at least.

Thanks in advance,
Col

 

[john61ct]

Measure the voltage at the battery posts both sides toward the end of a long drive. They should be the same or very close while they are combined, and only go down to different levels once isolated from each other.

If not either the solenoid / combiner whatever is broken, or connections are going bad.

Maybe get a pro in to troubleshoot, buy an ammeter / DMM get tgem to teach you how for next time.

 

[ColMonty]

Thanks John61ct.

I have been using a multi-meter (ammeter function) and measuring across the battery posts.

I've just driven 20 minutes or so and tested again - no change and the "Solenoid engaged" LED on the NL Intelligent Solenoid hasn't changed from yellow. I guess this indicates it is not engaged? The "Timer active" LED is green. I'd expect, logically, that these two LEDs would switch once the 5 minute timer is finished and the solenoid engages. I.e. they are mutually exclusive.

I have also tried manually overriding the timer, using the controller, but whilst the LED on the controller flashes red, nothing else changes.

To me it looks like the solenoid is never engaging.

 

[john61ct]

Replace with a standard ACR

This is the best, bulletproof lasts for decades https://www.bluesea.com/products/7620/ML-ACR_Automatic_Charging_Relay_-_12V_DC_500A

Likely overkill, but Blue Sea also has a range of lighter duty ones.

My preference is putting all charge sources direct to House, then a little Echo Charger can keep Starter topped up.

But some modern vehicles you can't do such drastic rewiring.

 

[john61ct]

Of course if Alt is the only charge sourse then a $50 ign solenoid will do.

The VSR / ACR concept is when you need two-way to/from both sides.

 

[DiploStrat]

...
To me it looks like the solenoid is never engaging.

It is purely anecdotal, but some on this forum have reported National Luna failures. Can you take it to, ideally, a National Luna dealer, or, alternatively, a good auto electrics shop?

As noted above, it is not hard to troubleshoot. With the engine on, the voltage on both sides of the relay should be the same, and they should both be near the maximum rated voltage of your alternator/regulator.

And another vote for Bluesea ACR's - I have never heard of one failing.

 

[john61ct]

The small ones do if overloaded. Some even try to self-jump through them, ampacity just not designed to handle that.

But the **specific** one I posted can handle anything and yes out of thousands of installs dozens of sparkies, never heard one of those failing.

 

[ColMonty]

Spoke to the UK NL reps. They advised me to reset it by disconnecting and reconnecting the black monitor wire on the intelligent solenoid. That has changed things as my aux battery is now appearing in alarm state - bottom two red LEDs are flashing on the controller and the audible alarm is going (I've disabled that now). I was hoping that running the engine would cause the voltage to jump up and the alarm finish, but no luck, though I only ran it for about 10 mins.

The truck is going into the local Toyota garage tomorrow for a new AC compressor, so I'll ask them to charge the aux battery - that'll buy me some time at least.

The Bluesea system sounds similar to the NL system, right? I doubt I can get that new system installed here in Italy in the next few days without speaking the language. And I'd rather avoid additional cost after the huge unexpected outlay for the AC.

The other suggestion from NL was that a fuse may have blown. I started checking every fuse I could find but nothing I found was blown.

I can hear the solenoid clunking on after 5 mins of the engine running, and the LEDs are correct, so I'm hopeful that it is merely a fuse blown somewhere.

 

[john61ct]

A VSR / ACR / combiner is not a "system", just a very simple device with one function.

A contactor opens (isolates) or closes (combines) the connection between two circuits,

just like a manual high-amp battery switch.

But automated, based on whether or not a higher charging voltage is present,

so if a charge source is active on either side, both banks get charged.

When voltage drops, they are isolated from each other, to prevent House loads from drawing Starter down and stranding you in need of a jump.

Very simple, very little to go wrong, and robust, long as you make sure (as with CP) to choose an ampacity greater than whatever current will be crossing the connection.

With the 500AH one I linked to, little concern about even that, as I said bulletproof.

 

[ColMonty]

Ok, point taken. Given I definitely do have a "system" installed currently, though, which gives a monitor and controller which can override connecting the batteries, the Bluesea relay feels like a backstop solution for me. I like the simplicity, don't get me wrong - I'm a big fan of Occam's Razor.

If I have no luck tomorrow I'll look into having one delivered to my exit port in Italy.

Thanks again, really appreciate the advice.

 

[DiploStrat]

FWIW Department: The National Luna "system" isn't much of a system. For reasons that have been beaten into the ground on this forum, a voltmeter on your second battery doesn't really tell you much. (A bit like trying to guess the contents of your fuel tank by looking at the speedometer.)

You really need a serious battery monitor, either a classic, shunt based monitor (e.g. TriMetric: http://www.bogartengineering.com), or, if you are more adventurous, the Smart Gauge: http://www.smartgauge.co.uk/smartgauge.html

So, should you choose to replace the National Luna with a Bluesea ACR, you are not really giving up anything. I would argue that the tell tale lights on the dash switch that comes with the 500A ACR is probably the most important thing, second only to a real state of charge meter for the camper battery.

Best wishes!

 

[john61ct]

Another great AH counting monitor /logger is Victron BMV-712.

Not quite as accurate as SmartGauge for SoC, but that has no ammeter.

I believe both display voltage-only for bank2, should be all that's needed for a dedicated Starter sits at 100% all the time.

 

[Bayou Boy]

I echo the above. There are tens of thousands of boats around the world running Blue Sea ACRs in significantly more harsh conditions than under the hood of a car that have been in operation for long periods of time without fail. Replace that whole setup with that Blue Sea kit above and go about your trip with zero worries.

I have the simple Blue Sea M-ACR on my truck to charge my Aux battery and it is flawless as has been the few I've installed on boats over the years.

 

[ColMonty]

So my aux charging remains inconsistent and unreliable. Sometimes it charges, mostly it doesn't - from the alternator. I have been hooking up a mains charger the past few days and it's had been slow - I think by the morning I should finally have a fully charged aux.

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.

The argument against this is that the main battery ALWAYS shows as being at maximum charge when the engine is running - i e. The voltage is much higher than when it's fully charged at rest.

What do you guys think?

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?

Thanks as always for your help

 

[john61ct]

Alternators do not think so much.

I would bypass the NL gear.

If you don't want an auto switch VSR,

put a manual high-amp battery switch between the two circuits and a voltmeter for each.

On is closed / connected, off is open / isolated.

On will show V is matched, Off they will differ.

Keep On while driving, turn off when stopped.