Thread: New deep cycle battery?

Shift the PAS reservoir. Make a steel flat bracket bolted to the support panel and bent slightly towards the engine. Then fit a full size battery, plenty of choices.

If you are getting significant voltage drop to the back of the disco you need to address the wiring from aux to fridge. Either 8 or 6 b&s wire will be enough for fridge alone. With correctly sized cable you should see only 0.1 or 0.2 volts drop.

Voltage drop under load at the battery terminals does suggest a dead battery however.

Traxide battery isolators are a pretty good way to get around battery size limitations, especially with a deep cycle/ cranking dual purpose battery for the starting battery.

Originally Posted by OffTrack

If you are getting significant voltage drop to the back of the disco you need to address the wiring from aux to fridge. Either 8 or 6 b&s wire will be enough for fridge alone. With correctly sized cable you should see only 0.1 or 0.2 volts drop.

Voltage drop under load at the battery terminals does suggest a dead battery however.

Traxide battery isolators are a pretty good way to get around battery size limitations, especially with a deep cycle/ cranking dual purpose battery for the starting battery.

OK, let me quantify this a little in case I'm talking B.S. Load is somewhere between 4 to 6A.

Battery open circuit: 12.4V
Battery with load: 12.2V

Rear plug open circuit: 12.35V
Rear plug with load: 11.2V

Soooo... battery, wiring, or both?

P.S. 8 or 6 b&s wire = american wire gauge? I'll have to check, but that sounds pretty big. I doubt what is installed is that thick.

Originally Posted by Judo

P.S. 8 or 6 b&s wire = american wire gauge? I'll have to check, but that sounds pretty big. I doubt what is installed is that thick.

B&S is pretty much the same as AWG.

You probably have a combination of tired battery and undersized wiring.

You need to factor in both positive and negative runs for total wiring length when calculating voltage drop. Providing you have solid power connections between battery and fridge a 10M run of 8b&s would drop 0.16V at 6amps. Typical "4mm" auto electrical wiring might only be 2mm^2 or 14 gauge or less so on the same 10M run you'd see a 0.5V drop at 6 amps.

I'd also be checking the wiring to make sure you haven't got any marginal connections between battery and fridge. 1V drop seems huge for wiring alone - sure it's not a 15amp draw?


cheers
Paul

OK, just got home so can clarify a few things.

According to the fridge manual, it cuts out at 10.8V and will only cut back in at 12.6V. (The "cut back" part sounds odd to me, but anyway).
From running the fridge through a 240V power pack and a watt meter on the DC lead, it draws about 4A.

The wiring to the rear socket has 16AWG stamped on it.
The fridge power lead also has 16AWG stamped on it! It's about a metre long.

So to summarise, yesterday I thought I was ready for my upcoming xmas camping trip.
In actual fact, I need to relocate my PAS reservoir, buy a new battery and re-run the wiring in a higher gauge.


How am I doing?

Originally Posted by Judo

According to the fridge manual, it cuts out at 10.8V and will only cut back in at 12.6V. (The "cut back" part sounds odd to me, but anyway).

The 10.8v is obviously a load voltage - when the fridge cuts out the battery will have a bit of a rest and the no load voltage will rise. If the cut back in voltage was 10.8v the fridge would start back up again but only for a short period so draining the battery further.

By having the the 12.6v cut in voltage this means that the battery has to be recharged (at least partially) before the fridge can be used again.

Garry

Originally Posted by garrycol

The 10.8v is obviously a load voltage - when the fridge cuts out the battery will have a bit of a rest and the no load voltage will rise. If the cut back in voltage was 10.8v the fridge would start back up again but only for a short period so draining the battery further.

By having the the 12.6v cut in voltage this means that the battery has to be recharged (at least partially) before the fridge can be used again.

Garry

I understand the theory. My concern is it seems high - particularly in my case where my battery open circuit voltage is only 12.4V! So it will never come back on? Anyway... I know what you mean.