Voltage Drop with fridge

Submitted: Monday, Feb 18, 2008 at 15:32
ThreadID: 54698 Views:2634 Replies:6 FollowUps:6
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Hi All,

I know this has been done to death, but what is the lowest voltage drop deemed allowable when operating a Waeco fridge?

Mine has suddenly dropped .5, normally it was only dropping .2.

Regards

JD
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Reply By: Derek from Affordable Batteries & Radiators - Monday, Feb 18, 2008 at 16:21

Monday, Feb 18, 2008 at 16:21
You would need to recreate the same test conditions.

Same temperature (Wire, relays, fuse etc)
Same battery voltage (This can affect the overall result)
Battery condition and SOC.

Try the same test using a fully charged battery.
AnswerID: 288157

Follow Up By: Treading Lightly - Wednesday, Feb 20, 2008 at 12:53

Wednesday, Feb 20, 2008 at 12:53
Derek, Sorry for late reply. Internet probs.

I have checked every thing again and here are thw results.

Engine running battery voltage (Aux) 13.98

Fridge running on turbo from ambient and set to 0.

Voltage at fridge plug (sharp meter leads into cable) 13.39

Result .59


With same meter and using jumper leads from + Battery to positive fridge lead a reading of .61 volts.

The fridge is powered directly from Aux Battery to a Merrit plug and socket in the rear (LC 100) approx 5 mtrs of 6 sqmm twin


Regards

JD
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FollowupID: 553754

Follow Up By: Derek from Affordable Batteries & Radiators - Wednesday, Feb 20, 2008 at 13:16

Wednesday, Feb 20, 2008 at 13:16
There is a problem somewhere.

You have the results for 2.5mm2 cable.

Try the same test with a 50W globe and not the fridge to see if it s the fridge at fault.

I also recommend you back probe the wiring and see if you can find a fault in the cable somewhere.

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FollowupID: 553757

Follow Up By: Mainey (wa) - Wednesday, Feb 20, 2008 at 13:45

Wednesday, Feb 20, 2008 at 13:45
JD, with engine running and Aux battery charging @ 13.98v is as close to 'normal' as you need.

With fridge running in turbo mode, and voltage at fridge plug @ 13.39v giving just 0.59v loss I would not be overly concerned.


You say:-> ""With same meter and using jumper leads from + Battery to positive fridge lead a reading of .61 volts""
Ummm, this is a BIGGER LOSS than when using the original cable.

You say:-> ""The fridge is powered directly from Aux Battery to a Merrit plug and socket in the rear approx 5 mtrs of 6 sqmm twin""
If the extension cable was replaced by a thicker cable you should have LESS voltage drop!!

Mainey . . .
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FollowupID: 553761

Reply By: Mainey (wa) - Monday, Feb 18, 2008 at 18:22

Monday, Feb 18, 2008 at 18:22
JD, if the Voltage drop has (suddenly as in recently) *increased* from 0.2v up to 0.5v (150 % *increase) with no other apparent changes then you must have a 12v battery power, or more accurately lack of 12v power, problem.

Mainey . . .
AnswerID: 288178

Reply By: Robin Miller - Monday, Feb 18, 2008 at 18:31

Monday, Feb 18, 2008 at 18:31
Hi JD

It doesn't really matter as long as the voltage at the fridge is enough.
Enough depends on the setting of the low volts cut-out , but 11.5 at the fridge is ok provided its measured when its running.

When measuring , switch the fridge to "Turbo" so volts are measured at max current.

Your different readings could be because it was in different modes and there really was no difference.
Robin Miller

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AnswerID: 288180

Reply By: Member - Phil G (SA) - Monday, Feb 18, 2008 at 19:35

Monday, Feb 18, 2008 at 19:35
JD,
Just wondering how you are measuring voltage drop.

Best way is to have one lead on the battery pos, the other hooked into the fridge lead, put your multimeter on the 2V scale and run the fridge. You'll need a multimeter lead thats 6 metres long though!

If you simply measure at the fridge outlet or thereabouts, you won't know how much the battery drops when you draw a load.

I cheat a bit - I let the fridge run a while, and while its cycling, measure battery voltage, and then subtract the voltage at the fridge connector.
AnswerID: 288191

Follow Up By: Treading Lightly - Tuesday, Feb 19, 2008 at 07:39

Tuesday, Feb 19, 2008 at 07:39
Hi Phi,

I measure the voltage at the battery, then measure the voltage at the fridge leads while the fridge is in turbo mode.

I use pin point leads and insert them into the insulation.

JD
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FollowupID: 553543

Follow Up By: Mainey (wa) - Tuesday, Feb 19, 2008 at 07:44

Tuesday, Feb 19, 2008 at 07:44
JD,
so the Voltage measurement *method* is the same and constant ?

Therefore ONLY the resultant Voltage numbers have changed !

Mainey . . .

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FollowupID: 553544

Follow Up By: Member - Phil G (SA) - Tuesday, Feb 19, 2008 at 22:17

Tuesday, Feb 19, 2008 at 22:17
"I measure the voltage at the battery, then measure the voltage at the fridge leads while the fridge is in turbo mode."

JD,
The fridge needs to be running when you take the battery measurement. The voltage of the battery itself drops (by maybe 0.3V) when your Waeco draws the 7 amps in turbo mode.

So BOTH measurements need to be done immediately after one another, and both while the fridge is cycling.
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FollowupID: 553702

Reply By: Member - Mike DID - Tuesday, Feb 19, 2008 at 11:00

Tuesday, Feb 19, 2008 at 11:00
Either -

1. Your fridge is drawing more current than before
2. One of the connections has corroded/overheated and gone high resistance
3. Something else is drawing current as well as the fridge.

Start working your way back from the battery measuring voltage and find out where the extra voltage drop is happening.
AnswerID: 288282

Reply By: Derek from Affordable Batteries & Radiators - Tuesday, Feb 19, 2008 at 21:55

Tuesday, Feb 19, 2008 at 21:55
Hi JD

I am still waiting for your test voltages.

Voltages / Load / Temperature all play a part.

If doing these sort of tests try recreate the same test conditions each time.

Regards

Derek.
AnswerID: 288375

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