still having dual battery problems

pommmy

New Member
got a mystery to solve............my dual battery system has been giving me problems for ages, thought i hd it sorted till my second battery wouldn't run my locker compressor, so i have the ute running, getting 13.9 volts at the front battery, 13.9 volts at the dual battery isolator, and 13.9 volts at the back battery led when not connected to the battery, when connected it dropped to 9.9 volts, so i disconnect everything and put my baack battery on charge over night, sunday morning its 12.2 volts, connect the system up apart from the back battery, 13.9 all around, hook up the back battery still 12.2...............................got me buggered, aany ideas?
 

Alien d2

4x4 Earth Contributer
What brand and type of isolator are you useing?
Are your testing votages at both 2nd battery terminals? Might be a bad earth lead.

I had a Parahna on mine that worked as often as not.
Best as we could work out it had a dry joint on the curcuit board.
I replaced it with a Red-Arc and I've had no dramas since.
 

cloughcarib

Well-Known Member
A fully charged batt should read 14.2V(approx), a fully charged batt under load should read no less than 13.8(approx)a discharged batt should read no less than 12.4 or the chances are that it's dead or needs fluid. That's if you're reading directly off the batt.

When I say Approx, I mean within 0.3V

If you're getting 13.9 with the eng on, you may have charge issues. I say may, because the problem could be contacts(the ground is the biggest prob here)

With your voltage drop, I would assume a contact issue, not charge or batt.

Check every wire and connection that leads from each batt. undo them all, sand(400g paper) them with wd40(or equivalent) and check again..

I AM NOT A TRADE QUALIFIED PERSON, but I'm sure you might get a response from one:)
 

monk2

Active Member
pommy i would be checking all my body earths and connections some thing crook when a bit of load comes on it
 

squizmark

New Member
1. If you are getting 13.9v whilst car is running, thats your first problem, should be text book 14.2v +/-, unless it has been draining for a while via ancillery equipment.
2. Your dual battery controller (if decent quality) will isolate second battery for a period till the start battery has regained charge from the starting of the engine.
3. I would get the charging system checked, and get the batterys tested or do it yourself.
Open all the screw caps, ensure there is electrolyte well over the plates, using a hydrometer (cheap from autobarn) each cell should have a specific gravity of 1.25 or close to.
Next to check for a dropped cell you can using a multimeter insert one probe in each cell on the plate and the other on a terminal and they should all be similar increasing as you move your way from terminal post used. If there is any major changes in voltage, that will be your problem cell. If they are all the same but low, your battery needs recharge or replacement.
Finally you can load test it with a carbon pile tester or rheostat, but if you had this equipment then you probably know how to do that. Should maintain a voltage of 10.5 ish volts at rated current.
If you spill battery acid, neutralize with washing powder. If you get it on your clothes, dont wash it with the wifes sunday best or it will become get none sunday.:D
I hope this helps you, any questions on anything electrical give me a bell. Good Luck!
 
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drivesafe

Active Member
Hi pommmy, to have 12.2v at the back battery with the motor running, could be caused by a dead cell or it could nothing more than your battery being low and needing a good charge but you could have a loose/bad connection somewhere or your cable is too thin or you have a bad earth return if your using the chassis as the earth return.

For a starter, if your battery was down to 9.9v depending on the type of battery charger you have, it could take a few days to get the battery back to a full charge state.

Next, what size cable do you have running between the two batteries and have you run a separate negative or just used the chassis?

As to the second battery, it may well have a dead cell and the easiest way to check is to put a load on the battery, say connect your compressor or some other load like a driving light.

If the battery has a dead cell it will drop to 10.5v in a few seconds.

If it drops to say 11.5v and stays there then there is a good chance your battery is just low and still needs more charging.

A fully charged battery with a small load on it should have a voltage of 12.6v to 12.75v. At 12.2v, if you have a load on it, your battery is at 60% charge capacity

If your alternator is the original then it would probably normally run at a little over 14v but 13.9v is fine for charging batteries and anything over 13.2v while charge a battery but it would just take a long time.
 

red hilux

Well-Known Member
1. If you are getting 13.9v whilst car is running, thats your first problem, should be text book 14.2v +/-,

Disagree with that.

I know stacks of cars that only charges at 13.8v, mine does too before and even after with the upgraded alternator (upgraded from 85 amp to 110amp)

13.9v is a good charge

he has either a battery or supply problem
 

squizmark

New Member
Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10-2.13V per cell)
Open-circuit at full discharge: 11.8 V to 12.0 V
Loaded at full discharge: 10.5 V.
Continuous-preservation (float) charging: 13.4 V for gelled electrolyte; 13.5 V for AGM (absorbed glass mat) and 13.8 V for flooded cells
1. All voltages are at 20 °C (68 °F), and must be adjusted -0.022V/°C for temperature changes.
2. Float voltage recommendations vary, according to the manufacturer's recommendation.
3. Precise float voltage (±0.05 V) is critical to longevity; insufficient voltage (causes sulfation) which is almost as detrimental as excessive voltage (causing corrosion and electrolyte loss)
Typical (daily) charging: 14.2 V to 14.5 V (depending on manufacturer's recommendation)
Equalization charging (for flooded lead acids): 15 V for no more than 2 hours. Battery temperature must be monitored.
Gassing threshold: 14.4 V
After full charge, terminal voltage drops quickly to 13.2 V and then slowly to 12.6 V.

When i said text book i literally meant it.

Ref:
Characteristics and charging techniques of Lead Acid batteries.
 

pommmy

New Member
Hi pommmy, to have 12.2v at the back battery with the motor running, could be caused by a dead cell or it could nothing more than your battery being low and needing a good charge but you could have a loose/bad connection somewhere or your cable is too thin or you have a bad earth return if your using the chassis as the earth return.

For a starter, if your battery was down to 9.9v depending on the type of battery charger you have, it could take a few days to get the battery back to a full charge state.

Next, what size cable do you have running between the two batteries and have you run a separate negative or just used the chassis?

As to the second battery, it may well have a dead cell and the easiest way to check is to put a load on the battery, say connect your compressor or some other load like a driving light.

If the battery has a dead cell it will drop to 10.5v in a few seconds.

If it drops to say 11.5v and stays there then there is a good chance your battery is just low and still needs more charging.

A fully charged battery with a small load on it should have a voltage of 12.6v to 12.75v. At 12.2v, if you have a load on it, your battery is at 60% charge capacity

If your alternator is the original then it would probably normally run at a little over 14v but 13.9v is fine for charging batteries and anything over 13.2v while charge a battery but it would just take a long time.

ok now i'm totally confused after these last few reply's lol, but here goes, the battery is almost brand new, not the best brand, (but all i could afford at the time), had it on charge over the weekend, and it went up from 9and a bit volts to 12.2v so i'm guessing no dead cell cos it charged on the 240v charger... as for the cables, they are pretty big, half as big again as a set of jumper leads (in diameter that is)
 

monk2

Active Member
pommy can you please put up a pic of second battery and where its mounted thankyou dose the earth from the second battery go to body of car or to chassis, cable that feeds the second battery you say is half as thick again as a set of jumper leads ?? 20amp leads or a real set of leads 250/300amp set that have some copper in them and not a lot of plastic covering them thankyou
monks
 

pommmy

New Member
pommy can you please put up a pic of second battery and where its mounted thankyou dose the earth from the second battery go to body of car or to chassis, cable that feeds the second battery you say is half as thick again as a set of jumper leads ?? 20amp leads or a real set of leads 250/300amp set that have some copper in them and not a lot of plastic covering them thankyou
monks

will get some pix after work tommorra
 
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