Very Bad Voltage Drop ??????

[guzzla]

Frist the history...

I recently moved my three batteries from the engine bay to behind the drivers seat on my 80s. They are all 130a/h Trojan Deep Cycle batteries. One battery is used for starting and the other two are wired in paralell. They are all connected using 70mm2 tinned copper marine cable with professionally crimped terminals. 2 x 70mm2 POS cables run into the engine bay to two studs. The starter motor is connected to the starting battery POS and the auxuillary fuse box connectes to the other. Another 70mm2 NEG cable runs to the engine block that also has 35mm2 NEG running from the engine to the chassis. I also have a 35mm2 NEG running from the engine block to the inner guard (both about a 500mm long). A Redarc solenoid is used to control charge to all the batteries.

After getting out the multimeters to find a bad earth problem highlighted by a malfunctioning headunit, I have noticed the following...

While the main battery reads 12.50v across the terminals, the AUX has 11.10 and both the measurements repeat themselves when tested at different points on the vehicle and in the engine bay. I also tested all the NEG cables and they show the same readings. When the engine is started, I get 14.4v across the main batery terminals and at the Redarc but the voltage drops to 9.67v across the Aux abtteries and on the Aux side of the Redarc. I suspect that the AUX voltage of 11.10 is because the fridge has been running off the AUX batteries for about 8 days and not getting any charge.

I have done some decent winching in the past through the Redarc and suspect it may have given up the ghost but I can still hear the relay click in and out. I don't understand why the AUX batery voltage drops when the engine is started. Even after a 45min drive, the Aux batteries remained at 9.67v. Both POS terminals on the AUX batteries have started to get corrosion on them too, but not the starting battery.

It would be great if someone could confirm what I think I already know - that the Redarc is dead???? or is it something more sinister???

Also, if the Redarc is considered dead, should I replace it with same or something better?

Cheers,
Nathan

[drivesafe]

Hi guzzia, I’d say it sound like your Redarc is probably stuffed but it’s probably stuffed because of using it for winching.

If it’s worked so far, I’d replace it with another Redarc and I believe they now make a model that will handle winching.

As to your auxiliary batteries still being low after you start the motor, I’d go check all your earth connections again.

[+dj_hansen+]

Its not possible that 1 of your batteries is crook and dragging the other down (talking about the aux here and they are in parallel)

As for the redarc, you need the sbi212 model....

http://www.redarc.com.au/pdfs/Specs/Sma ... t-A5-2.pdf
http://cgi.ebay.com.au/Redarc-DUAL-BATT ... 125001r239
http://www.sidewinder.com.au/page165a.html

[gp339gm339]

I would suspect a faulty cell in one of the batterys, try disconecting one battery at a time and see what happens

[Gonzo]

A dud battery is my guess also. Try isolating them and see.

[its aford not a nissan]

unless i have missed something obvious he was asking if the redarc is dead or not , obviously if the redarc isnt working the aux batts will be reading low , as for the aux batts reading lower with the engine running he either has something running off them when the motor is running or the redarc is stuffed enough to cause a short , but reading his post sounds like he runs everything off the aux batteries and the main batt for starting and winching only

and yes get a bigger redarc or even 2 of them

[guzzla]

Hi guys thanks for the replys.

I've double checked all the earth cables and fitted another from the chassis to the gearbox and chasis to body. More so just to make sure as I couldn't find any voltage drop at any of the existing earth points.

I'm convinced the Redarc is dead and have a mate ordering a 140amp Bluesea VSR that should turn up early this week. I'm sure this will fix all my problems as the little control module on the redarc is a little deformed to say the least.

I'm pretty sure it's not the batteries as they've been working fine until now and the only reason they lost so much voltage in the first place was because the 80l Engel had been running off them for the last 10 days without any top up charge.

I guess I'll know soon enough when I put the new VSR on and I'll keep you posted.

Regards,
Nathan

[me3@neuralfibre.com]

Voltage difference between 2 "things" on the same wire, can only be caused by resistance and current flow.

So - if they are connected, and the voltages are different, there is a resistacne between them.

If you put a multimeter across the thing you suspect as being the point of resistance, you'll see a voltage.

There should be essentially no measureable resistance across a good chunk of wire, or a good relay.

If there is a voltage, then there is a resistance, and it;s faulty.

You do need to test is under load of some type, but a partially flat battery trying to charge from a full battery, is a load.

Hope this helps.

Paul

[Harb]

yep, just fire the truck up.... make sure the little red light is "on" on the redarc and then put the red lead off you multimeter on the incoming power side of the solenoid, and then the black lead of your multimeter on the other solenoid post, the outgoing one that goes to your aux batteries and then read what the multimeter says on the DC volts setting.
This will measure the actual voltage drop across the contactor.....
It should read very low.....minimal voltage drop across the solenoid contacts (The Big terminals) if it reads in this case 3 or 4 volts from what I am reading here, the redarc is stuffed.
Make sure it (the redarc) is getting full voltage by first measuring between the incoming terminal and chassis ground....... and that the Light is on when you do the drop measurement.

[me3@neuralfibre.com]

Re. the dropped cell theory. A dropped cell in one battery would bring he voltage down on ALL things on the same wire.

If they are on a (suitable) wire - they have to be the same voltage.

Paul

[gp339gm339]

I suspect both the batterys and redarc unit may be faulty.

Try charging the batterys with an external battery charger

[guzzla]

Hi guys,

A put in a new VSR and it's working perfectly now.

Even the head unit works that I was having difficulties with in another thread.

Thanks for the tips guys. They all helped narrow it down.