Thread: Battery question

just checked that link. you will need to click direct current comp+ bd50(first one)+bd series to get there.

Originally Posted by crump

Got 11.6v across the terminals and at the fridge outlet first thing this morning after having the fridge running all night(and it had cut out).Started the car and let run for 5mins and switched off, both points read 12.4v.I get the same readings on the batt and at the end of the fridge plug, so volt drop isnt the problem.

Sorry Crump, I find this very hard to believe unless your fridge is right next to the battery and has very heavy cables to the battery.

IF the fridge is running and drawing, say, 4 amps, then there will have to be a voltage drop along the cable.

Umm, you aren't running superconductor cables are you?

Ron

Hi crump, most bases have been covered but one.

How charged was your battery before you put the fridge on.

The voltage reading you got after the 5 minute charge you gave it would have been the surface charge and would not give you any true indication as to the state of charge of the battery.

Try testing the battery after you have driven the vehicle for a few hours.

Also try testing the voltage at the fridge after you have been for a short drive, 15+ minutes, leave the motor running and see if there is an improvement in the voltage at both the battery and the fridge.

Start there and see how you go.

Now, as to the cut-out voltage, Blknight posted the likely reading after a cut-out occurs. The voltage reading while a load is applied to a battery will always read lower than the battery’s actual State of Charge ( SoC ) voltage.

The lower the SoC of the battery and the higher the load applied to the battery, the greater the difference is going to be between the cut-out voltage and the battery’s settled voltage. If your battery is fully charged and you applied a load and measured the battery terminals, your actual SoC and the measurement reading would probably only have a difference of no more than .1 to .2 volts.

The reason for this is that the battery’s voltage reading is not proportional to the battery’s SoC. With a fully charged battery, you could use 10% of it’s stored capacity and only get a .2 volt drop in voltage. Whereas between 10% SoC and 0% you would get nearly a full volt drop.

So with a low SoC, it will only take a very short time for the battery to be completely flattened and DAMAGED, but as the battery only requires a very small load to pull down the terminal voltage to a much lower voltage than is in the battery, the battery is virtually self protecting.

This is very convenient for fridge manufacturers because if the battery was under a constant load that actually pulled the SoC down to 10.3 volts, you would only need to do this a couple of times and your battery would be stuffed but because the terminal voltage is easily pulled down bellow the actual battery voltage, there is far less chance of damaging the battery.

Most batteries DO NOT like being discharged bellow 11 volts ( SoC ) but even when a device with a cut-out voltage of 10.3 is used with a battery, the battery is not drained to that voltage BUT if a device does not have a cut-out voltage you MUST remove it once the battery voltage drop to 11 volts to avoid damaging the battery and shortening it’s operating life.

BTW, like Ron posted, I to would be very surprised if you didn’t have at least a small voltage drop between the battery and the fridge ( but thats another subject )

Cheers and sorry for the long winded reply.

Originally Posted by p38arover

Sorry Crump, I find this very hard to believe unless your fridge is right next to the battery and has very heavy cables to the battery.

IF the fridge is running and drawing, say, 4 amps, then there will have to be a voltage drop along the cable.

Umm, you aren't running superconductor cables are you?

Ron

"....after having the fridge running all night(and it had cut out)....." I read this as the fridge had cut out, and hence was drawing no or almost no current. If that isn't what he meant, I agree with you!

John

took the car to the not so local wrench and he tested both batterys with one of those u beaut diagnostic thingos, and both are fine, so its the fridge thats rooted, great another warranty headache.

Crump,let us know how you get on trying to get warrenty for that problem.I spent many weeks trying to sort a problem with mine .fridge was ok with truck running but when stopped it would be ok til volts dropped down to 11.8.fridge would try to start,fan would spin then fridge would shutdown.30 secs later same thing all over again.no help from wea** so did some digging on danfoss site.set cut/out and no more problems.have reset caravan (bd35) same. have had NO problems with my batts(over 2 years) and both are used appox20 weeks per year.

got it mate reply sent

Originally Posted by rangieman

Also make sure that you have a earth aswell as the power from your Aux battery running to your Aux power socket for the fridge

Reason being who ever wired my car up before i bought it used the dual core wire for 2 positives to 2 sockets and just run earths from both sockets to the body it caused all sorts of drama,s($$$$$) till i worked it out

The body is the biggest conductor possible,better than any wire, so unless the body wasn't earthed correctly this has to be the best set up.