Battery question

[crump]

What volts should a healthy 12v battery show on a multimeter across the terminals?

[ladas]

What volts should a healthy 12v battery show on a multimeter across the terminals?

If it's disconnected from the car - and is fully charged - then in excess of 12.2v - If it's connected to the car there may be 'something' draining the charge - computers/lights etc.,

If it's connected to the car and the engine is running then about 13.5 v

However the volt measurements will not always tell you if a battery is healthy -

[crump]

I'm getting 11.6 at my fridge outlet from my auxillary battery and the fridge keeps tripping out, so is it more than likely the battery is the problem??

[Blknight.aus]

possabley not between your hookup point and your battery you could have a bad earth...

grab the biggest headlight (110 watts worth should do for a field check) that you can find, hook that up directly to the terminals and then read the volts.

A perfect battery will stay over 12v (for a little while anyway)but only just and if it reads anything under about 11.5 then its on the way out but not done yet. Anything under 10 is bad.

If it will hang on till i get back from course I'll put it on the toaster for you and let you know how it really is.

[weeds]

it could be a combination of wiring and battery

what is your actual voltage at the battery, rested i think is the term, say first thing in the morning after it has been sitting all night, if this is somewhere over 12V than i would look at your wiring

you could buy an engle as they don't have low voltage cutout fitted........umm not good for you battery though

[p38arover]

With the fridge running, check the battery voltage at the battery and then at the fridge.

Subtract one from the other to find out the voltage drop along the supply cables.

It should be low. If not, the cable is too small for the load. How low is low? Hmm, hard to say but I'd be looking for less than 1 volt. Drivesafe will have a better view than me.

Tell us what you measure and we can discuss that.

Ron

[crump]

what I'm trying to work out is whether my problem is the Batt or the fridge.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.Voltage cutout on the CF 40 is supposed to be 10.4 on the low setting, which is where I have it set.Why do these things happen before a fishing trip?:mad:

[Blknight.aus]

ahhhh...

Did you check the voltage at the battery and the socket with the fridge in and running...

Voltage drop on a cable will only be apparent while under load unless there is a high resistance earth/connection somewhere.

If the battery isnt as healthy as it could be you might find that its dropping below 10.4 and then tripping the battery protector but isnt "recovering" enough to reset the protector.

Big reds Aux battery is doing this when running the aircompressor (engine off) now so it cant be long till the fridge starts doing it too. 3+1/2 years out of one battery isnt bad and the primary still tests ok with plenty left on the pass mark....

[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 :cool:

[crump]

12.4 at fridge socket when running fridge.

[tracker]

http://www.danfoss.com/Products/Categories/Categories.htm'segment=RA&category=http%3a%2f%2fwww.ra.danfoss.com%2fra%2fPr oducts%2fProductCatalogue.asp%3fNavigation%3dHideO nAllPages%26Footer%3dHideonallpages%26Division%3dC C%26HL%3d1%26TopViewItem%3d74%26AppID%3d%7bc2a95da c-5e01-47df-92cd-5972d837cf1a%7d%26dyn_lang%3d
That should get you to danfoss web site,open literature on bd35(250k english)(should be your compressor) and scroll down to batt protection settings. I set my bd50(weaco) and bd35(isoferm) to a value of1K cuts out at 10.8appox. Battery is 4 years old and has had no problems. Try it cost is sfa but you may have to replace pop rivits with (aussie?) ones.
cheers Brian

[tracker]

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

[p38arover]

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. :confused:

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? :eek: :D

Ron

[drivesafe]

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.

[JDNSW]

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. :confused:

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? :eek: :D

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

[crump]

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.:(

[tracker]

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.

[tracker]

got it mate reply sent

[County3.9]

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 :cool:

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.

[JDNSW]

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.

Correct as far as it goes - but if it is a Series or Defender Landrover (or early RR, and to some extent later RR and Disco), the body is made up of a large number of pieces of metal, bolted or rivetted together, with both pieces of metal painted at the joints, and often with dissimilar metals at the joints. These numerous joints notoriously cause frequently intermittent voltage drops. The only safe earthing on these Landrovers is the chassis, and even here the earthing points are often in positions exposed to water and road dirt and hence subject to corrosion. It is not safe to assume that the body forms a good earth return on these vehicles.

John