Unsavoury language and voltage drop
Submitted: Monday, Apr 25, 2011 at 13:35
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Member - Corrugate75
G'day,
Having spent the best part of
Easter Weekend installing a better upgraded 12v system through the camper trailer I also installed an isolation switch recommended by my local autoelect man.
Upon testing the system I seem to have 0.7volts drop across the isolation switch - 12.9v across the battery, then 125mm (5inches) of 6B&S cable to the isolation switch and only 12.2volts out the other side!
Needless to say there was some bad language used. I've done everything possible to avoid voltage drop and yet, induced a problem I think?!
Have I used the wrong isolation switch, or is this to be expected?
Thank you in advance for advice...
Cheers
Corrugate
Reply By: Notso - Monday, Apr 25, 2011 at 14:09
Monday, Apr 25, 2011 at 14:09
How many amps are you drawing?
Is there any heat build up in the joints or the switch.
AnswerID:
452256
Follow Up By: Notso - Monday, Apr 25, 2011 at 14:27
Monday, Apr 25, 2011 at 14:27
Should have also asked where are you earthing the voltage meter.
FollowupID:
724933
Follow Up By: Member - Corrugate75 - Monday, Apr 25, 2011 at 14:31
Monday, Apr 25, 2011 at 14:31
G'day. Switch is made by AutoElectrical Distributors 12v 50amp.
The drop I'm measuring is straight across the terminals, negative on the battery both times, positive on the battery 12.9volts, positive after the iso switch 12.2volts through 6B&S cable.
I'm overlooking something simple aren't I?
FollowupID:
724934
Follow Up By: paulnsw - Monday, Apr 25, 2011 at 15:03
Monday, Apr 25, 2011 at 15:03
Poor crimp terminal or bad solder joint?
FollowupID:
724938
Follow Up By: Notso - Monday, Apr 25, 2011 at 15:37
Monday, Apr 25, 2011 at 15:37
Is there any load on the system whilst you are testing the voltage? Or is the meter the only thing across the terminals?
FollowupID:
724942
Follow Up By: dbish - Monday, Apr 25, 2011 at 15:59
Monday, Apr 25, 2011 at 15:59
Sounds like its a battery isolator diode to have that amount of voltage drop. Should be using a voltage controled isolating relay then theres no voltage drop.
FollowupID:
724946
Reply By: Crackles - Monday, Apr 25, 2011 at 15:41
Monday, Apr 25, 2011 at 15:41
Stab in the dark but are you talking about one of those useless red key isolation switches by any chance?
Cheers Craig...............
AnswerID:
452265
Follow Up By: Member - Corrugate75 - Monday, Apr 25, 2011 at 16:34
Monday, Apr 25, 2011 at 16:34
Nail on the head Craig, err... what do you mean useless?!!!
FollowupID:
724948
Follow Up By: Crackles - Monday, Apr 25, 2011 at 17:45
Monday, Apr 25, 2011 at 17:45
Have seen many problems with red key switches of different brands including voltage drop to complete open circuit. By switching your multi meter to ohms you could try measuring the resistance accross the switch terminals. Any reading above .1 is bad. They are a sealed unit that can't be adjusted although you could try repeatably switching on & off to see if you can improve the internal contacts otherwise take it back and get something decent like one of these
Mini ON/OFF Battery Switchs
(Hit Battery switches tab top right)
Cheers Craig...............
FollowupID:
724952
Follow Up By: Member - Phil G (SA) - Monday, Apr 25, 2011 at 19:47
Monday, Apr 25, 2011 at 19:47
Gday Craig,
You warned me about those switches last year - since then had one fail on Amy's 80series and one fail on
mine. Replaced
mine with a Blue Seas switch that has 300A continuous rating (key switch was only 100A).
FollowupID:
724964
Reply By: Member - John and Val - Monday, Apr 25, 2011 at 21:08
Monday, Apr 25, 2011 at 21:08
And the answer to Notso's key question? How much current was flowing through the switch when you took your measurements?
A better way to measure the voltage drop across the switch is to connect the meter directly across the switch, not measure two voltages to earth. The voltage directly across the switch will depend on the current going through it, hence Notso's question. With a few amps running through it and by measuring right at the switch then moving progressively outward you should be able to narrow it down to the switch itself, or the crimped (?) terminals, the connecting wire, battery terminals..... I'd
check for any voltage between the battery terminal post and the terminal that's clamped onto it - might look like a good tight metal to metal bond, but can corrode in there and cause losses. With a few amps flowing you shouldn't see more than a few millivolts drop anywhere. (Of course with no amps flowing you should see no voltage drops at all.)
Cheers
John | J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein
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AnswerID:
452297
Reply By: workhorse - Tuesday, Apr 26, 2011 at 09:25
Tuesday, Apr 26, 2011 at 09:25
Good timing. I was about to set off yesterday and noticed the voltmeter reading low on the second battery which has one of those red isolator switches on it. Same 0.9 voltage drop across it, so I simply bypassed the switch and back to full power. This must have been a gradual decline in its operation over the past few months as I monitor the voltage regularly.
I also need to replace it with better quality unit. Any suggestions appreciated.
Thanks,
Michael
AnswerID:
452325
Follow Up By: Crackles - Tuesday, Apr 26, 2011 at 15:15
Tuesday, Apr 26, 2011 at 15:15
Blue Seas have a large range starting from 250 amp upwards. When working out the size don't forget to allow for loads of up to 450amp if winching through them. This is the single biggest reason for failure of the red isolator type switch that I've seen.
Cheers Craig..............
FollowupID:
725022
Follow Up By: Member - Corrugate75 - Tuesday, Apr 26, 2011 at 17:54
Tuesday, Apr 26, 2011 at 17:54
Thanks Crackles,
I'll get too and replace
mine too. I did such a neat job it'll take a while to find the enthusiasm again!
I just thought I'd put in the switch so when I'm travelling - all power to light points etc is off while canvas is folded, and when we arrive, set up canvas, turn isolation switch and all works. Nice idea but not with voltage drop through switch. I've checked a couple of times today (trailer stationary inside shed) and switch sometimes gives no voltage drop, sometimes 0.5 etc, so must be switch points not always connecting fully.
Thank you for help and advice.
Greatly appreciated.
Cheers
Corrugate
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