Problem with Redarc Battery Isolator / Secondary Battery

I have a secondary battery that lost it's charge. While investigating I noticed that the Redarc battery isolator was behaving unexpectedly.

The isolator would briefly light up, then immediately turn off. The negative lead from the secondary battery, which leads directly from the negative terminal to the truck body, would jump each time. This process would repeat itself as you can see in the video. When the engine is turned off, this process continues for another minute or so. Any idea what the issue might be or how to diagnose it?

The primary battery has a charge just over 12.7 volts.

https://www.youtube.com/watch?v=UEgP1TPAf8A

Thanks in advance for any suggestions!

A bit of a guess on my part.

First the red(!) negative wire appears to 'twitch' in response to the VSR (Voltage Sensitive Relay - ie the battery isolator) switching on/off - a physical response to a slight movement of the relay moving? Try ensuring it is securely mounted.

However the real issue is why it is switching on/off. Only thing I can think of is that the voltage it is receiving from the crank battery is unable to be sustained above it's required threshold. ie it turns on (connects crank & aux batts) at a crank battery voltage of 13.2v & off (disconnects) at 12.7v.

First up, try charging your Aux on a mains charger before doing anything else. Top up fluids first. You may find that once it has been charged the problem goes away, as it may be that a *very* flat battery (below say 10.8v) may be 'sucking too much from a crank battery which cannot supply what it needs without dropping below 12.7v itself.

If your aux battery is that flat it may need replacing as the chances are if a mains charger wont charge it it's effectively dead. If this is so - in future don't flog the aux battery - ie try to not take it below around 12.1v to 12.2v - that way it'll last a lot longer. Below 12v is battery killing territory.

If that is what has happened, the VSR has saved you from flattening the crank battery, allowing you to still start the car. In other words it's done the job it was designed for.

HOWEVER, whilst I suspect the above is probable, I also think that perhaps, on the basis of how quickly the VSR switches on then off, that your crank battery, is also not very healthy. It may start the car, just, but to me it looks like it drops the voltage way to quickly - even with the motor running. You should check the fluids in it are above the plates (if you can) & then also charge it fully on a mains charger. It may or may not be in need of replacement too.

Before removing the crank battery to charge it, & whilst you have the aux battery removed disconnected ..... Start the car & see if the VSR clicks on/red light shows ... & stays on. If it does it is an indicator that it is not the VSR at fault. ..... I *think*.It's a long time since I last used a VSR in my systems - I don't *think it needs to be connected to the Aux to switch on/off - it 'reads' crank battery voltage for that.

With the engine running use a multimeter to read the crank battery voltage across it's terminals - you should observe it slowly rise up to between 14v & 15v. This may take a little while so ensure it's somewhere with plenty of fresh air.
Regardless of whether it reaches over 14v (preferably 14.4v ), take it off & put it on the mains charger. If it does not reach this voltage you either have a duff battery, a duff alternator or both. If it charges up fully on a mains charger the finger points to the alternator.

One other possibility if the crank battery & alternator prove to be ok is that something between the crank battery & the VSR (or possibly between the VSR & Aux battery) is creating a significant voltage drop. Voltage drop is far worse & more noticeable at higher current (amps). Look for poor connections/wiring too thin & feel methodically along the line. Anything getting hot is a likely culprit.

If everything checks out ok, then it may be time to replace the VSR, but I doubt from the way it's behaving that it is the problem.

BTW...... the protocol generally preferred here is that new folk usually introduce themselves in the Introduction thread before launching into questions. Perhaps if you do that now, you might get a bit more response from others. ;)

A couple more thoughts.

The wiring you have does look on the thin side. The following chart from Redarc says what minimum thickness of copper you need. I always use heavy battery cable for connecting batteries!

Attachment 81827

Also it looks like you may have an auto reset contact breaker. If so it could be the on/off problem - get rid of it & fit a fuse or a manual reset CB - they are unreliable & make fault finding a nightmare. It is probably nowhere near the 60 amp or 100amp rating you need either. Do this first.

Attachment 81828

A bit more info would assist - have you had this set up working as it should over a reasonable period of time, or is it new to you (somebody else's work inherited with the car)?

@Cuppa has covered most things except that the isolator has an on/off delay.. Ie less than 12.5v for >5seconds will disconnect. It shouldn't connect/disconnect immediately so t looks like it's probably fried.

Make sure you charge that aux battery on a charger and not with your alternator. Isolators are a great cheap way to make sure you get home but are pretty hard on the batteries, especially if you run the aux battery down. Dc-dc charger is what you want if you have the coin.

No disrespect Cuppa! The rest was spot on!

Quote:

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Originally Posted by 0-TJ-0

@Cuppa

No disrespect Cuppa! The rest was spot on!

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None taken 0-TJ-0 - as I said it's quite a while since I last used a VSR ..... moved on to dcdc charging years ago I'd forgotten about the delay.
I would however, before replacing the VSR, replace that auto reset circuit breaker if it is what I think it is. I had one for my BCDC1240 at one time - & when it failed it would switch on/off rapidly, took ages to suss out what the problem was!

My suggestions...
Take that Auto C/B out and give it to a Cruiser owner or turf it in the nearest landfill and use either a fuse or manual reset C/B.
Upgrade any under spec wiring as prev suggested.
Then fault find if the problem persists

The VSR may be faulty but IMHO it looks like it is trying to connect when the engine is running and immediately after shutdown until the Cranker surface charge drops below the Redarc Low Voltage cutoff.
That is why normally the Redarc or any VSR will hang on for a while after the engine stops if there is no load on the batteries.
Even on hi parasitic drain vehicles like my Y62 with delayed cabin lights etc you won't hear/see the VSR drop out for maybe 30 seconds to a minute after the engine shuts off

FWIW I have only ever used quality VSR (Redarc, Invensys, etc) and not bothered with DC/DC on any vehicle mounted Aux Battery systems.
For trailer/van/exotic battery tech or constant cyclic use yes I do go for DC/DC but standard applications no need usually.

Never had a decent VSR fail yet as they are very reliable (and at work some of them are in very harsh environments) but like any elec component they obviously can, just very rare

Thanks guys, much appreciated. I have replied in full but it needs to be approved by a moderator before it shows up. I think it's because I wrote the reply in another program while I was flicking back and forth testing stuff, so I think the forum falsely detected me as a spam bot when I copied and pasted it all to the thread as a reply (they tend to detect typed-too-fast replies) :P