Battery voltage

Submitted: Saturday, Jun 12, 2004 at 23:13
ThreadID: 13717 Views:1794 Replies:6 FollowUps:4
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Evening all,
Built a kit from Jaycar today which will sound an alarm when the voltage of the battery drops when I'm using accessaries like the compressor etc.
But it is adjustable to scream at any thing from 8 up to 12 volts. Where should I set it so that it will go mad just before my Exide Extreme battery fails to start the 3litre V6? In other words below what voltage will the battery fail to start the car?
Thanks in anticipation,
Camper
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Reply By: Mad Dog (Victoria) - Saturday, Jun 12, 2004 at 23:36

Saturday, Jun 12, 2004 at 23:36
Compressors draw a large current and will give the cutout a false impression of battery state. Have the engine running when using the compressor. At 12 volts with a very light load the battery is 50% depleted. If running a fridge overnight I'd say set it to 11.5 - 11.8
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Reply By: Peter 2 - Sunday, Jun 13, 2004 at 07:44

Sunday, Jun 13, 2004 at 07:44
I would set it slightly lower around the voltage that most frigs will cut out, just under 11 volts. Most vehicles (especially petrols) will start at this point. Being adjustable you can easily reset it.
Peter
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Reply By: Bonz (Vic) - Sunday, Jun 13, 2004 at 09:06

Sunday, Jun 13, 2004 at 09:06
An ARLEC battery load tester would say your battery is OK under load at anthing over 8 volts, which i reckons a bit low but its under load remember. I am with Mad Dog, 11.5v is enough for a prolonged load on the battery.
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Follow Up By: Mad Dog (Victoria) - Sunday, Jun 13, 2004 at 18:30

Sunday, Jun 13, 2004 at 18:30
Good God, at 8 volts I'd say it's dead. My new n70zz only drop to 10 volts during cranking...how many amps is that..5 or 600
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Follow Up By: Bonz (Vic) - Monday, Jun 14, 2004 at 08:43

Monday, Jun 14, 2004 at 08:43
Wouldnt be any more than 50 amps I reckon judging by the size of the leads it was connected with, probly even less. My Original Battery went down to 8.5 v on the tester (which it would say os ok) but I replaced it anyway.
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Reply By: Phil G - Sunday, Jun 13, 2004 at 12:06

Sunday, Jun 13, 2004 at 12:06
That kit interests me. Not sure when I'd use it. Having an alarm go off in the middle of the night when the fridge draws down on the battery may not be popular. Any ideas??

I think you'd be better off with a low voltage cutout. The kits or premade versions that Jaycar and Dick Smiths stock are good, provided you're happy for the fridge to stop working until the morning. I used the relay type kit for a long time, and last year made up the transistorised kit. I used a potentiometer to make the cutout voltage adjustable.
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Follow Up By: Member - Camper (SA) - Sunday, Jun 13, 2004 at 21:43

Sunday, Jun 13, 2004 at 21:43
Thanks, Phil
The kit is in the latest Jaycar cat. p10 No kf-4010 cost about 10 bucks, tho they list it as 13.95.

I don't run a fridge and most stuff which might cause a problem I run off the battery direct so a cut off is not suitable I figured.
Plus I thought an alarm in case any drain like camping lights depleted the battery too far might be useful.

Camper
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Reply By: Member - Camper (SA) - Monday, Jun 14, 2004 at 20:42

Monday, Jun 14, 2004 at 20:42
Thanks to everyone for your help.
I'll do some experimenting around the 11-11.5 volts and see how I go
Camper
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Reply By: Biggus - Monday, Jun 14, 2004 at 20:46

Monday, Jun 14, 2004 at 20:46
Just for information sake, i have a Prado Turbo Diesel which has (2) 6month old batteries (exide extreme 620cca) to run fridge/lights etc and a (marshall 600cca) which was a warranty replacement for the main battery. I inadvertently left the interior light on for @ 24hrs, at that point the main battery voltage had dropped to
11.8v, the engine would not even kick over to start,i jumped started the car off the auxilary battery (handy), drove the car to work @ 20mins, checked the voltage again that afternoon before returning home and it had risen to 12.2volts the engine started but it was a bit slower than usual. Shows that a second battery is a great investment if your forgetful like me or if your fridge used just a bit more power than you expected and you only have the 1 battery.
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Follow Up By: Mad Dog (Victoria) - Monday, Jun 14, 2004 at 21:20

Monday, Jun 14, 2004 at 21:20
Interesting Biggus. I guess with glow plugs to run and the high compression of a diesel it requires a lot more grunt than a petrol.
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