[volt-nuts] Fluke 883AB differential voltmeter

[Brooke Clarke]

Hi Alan:

If the factory battery was Ni-Cad it's a mistake to replace it with 
Ni-MH.  During charging they are very different and the Ni-MH might 
overheat.  Is there a temperature sensor as part of the charging 
electronics?

Have Fun,

Brooke Clarke
http://www.PRC68.com


Alan Scrimgeour wrote:
> I also recently restored a Fluke 845AB  Null Detector. I used cheap 
> Nickel Metal Hydride batteries to replace the originals, but I was 
> tempted by the improving capacities of Low Self Discharge NiMH batteries:
> http://en.wikipedia.org/wiki/Low_self-discharge_NiMH_battery
>
> The repair seemed to work very well, but a fault quickly developed: 
> when switched to 'LINE OPR' (mains powered) the meter swings to the 
> extremes and then settles to zero and won't move again as though it's 
> switched off. I'm too busy to deal with that right now, but I was 
> wondering, how much noise should I expect to see in the meter needle 
> with the input shorted?
>
> Alan
>
>
> ----- Original Message ----- From: "Mark Sims" <holrum at hotmail.com>
> To: <volt-nuts at febo.com>
> Sent: Friday, March 19, 2010 1:04 AM
> Subject: [volt-nuts] Fluke 883AB differential voltmeter
>
>
>>
>> I just finished restoring a Fluke 883AB differential voltmeter (and a 
>> 845AB null voltmeter).
>>
>> The 883 AB needed new battery packs (I used 4 x nine AA cell nicad 
>> packs and a 4 subC cell pack)...  remarkably cheap from a Ebay 
>> vendor.  The original 9.6V packs used an unobtainium coin cell and 
>> would have cost around $200 to replace).  Also the power supply for 
>> the AC input converter was fried (transistor, zener, cap).
>>
>> Final problem was it would not zero properly.  The zero circuit uses 
>> two diodes to make a +/- 0.6V supply driving the offset pot.  The 
>> unit was offset so that you could not reach zero and the offset pot 
>> had fairly little range.  Adjusting the chopper didn't help.  I 
>> replaced the diodes with three 1.2V reference chips (making a -1.2 to 
>> +2.4V supply).  This centered the zero adjustment and gave better range.
>>
>> Adjusting the KVD is a pain...  you have to unsolder/solder various 
>> jumpers, etc.  Anyway,  it now seems to be working better than new.
>>
>> Now to the Fluke 515A calibrators.  They have two 18 (AAA?) cell 
>> packs. Replacements can be had for $175...  I think I can do better 
>> (or will do without).
>>
>> I also have a Space Labs digital igniter tester (basically a Kelvin 
>> ohm meter).  Uses a 6 cell NiMH coin cell pack built into a piece of 
>> PVC pipe. One place wanted $600 for the replacement!   Since the unit 
>> only draws 11 ma while you hold the test button,  I replaced it with 
>> a 9V smoke alarm battery / diode to block charging.  Should last 
>> forever (and not self discharge in a month)
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