[volt-nuts] Fluke 883AB differential voltmeter
brooke at pacific.net
Fri Mar 19 16:43:27 UTC 2010
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
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:
> 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?
> ----- 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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