Products > Test Equipment
Fluke 8600A Battery / Power Supply Conversion
xrunner:
New project arrived yesterday - a Fluke 8600A w/battery option.
This unit is extremely clean, and it really has only one small problem - it doesn't work. But I believe the reason it doesn't work is because this unit has the battery supply option, and the batteries are totally shot. Some of them look to be original NiCads. Now you may ask, well, just flip a switch inside to make it run off the mains, take out the batteries, and call it a day.
'Fraid it doesn't work like that. :(
It has to have the batteries to work because it essentially runs off of 5V, and has a DC-DC converter that provides +/- 15V all the time, powered by the batteries, all the while the batteries are charging. No battery - no worky.
Well, why don't I replace the batteries then? Because I'm not interested in running it off NiCads and I don't want to buy any D-size NiCads, especially for a unit that might sit for a long while without being used. Any future use would be for a benchtop DMM anyway. No, I'm going to convert it to let it run off the mains all the time. I also want the conversion to be minimally invasive to allow some future owner to restore it to it's original condition easily, if they so desire. I've researched some other people's ideas, some here on this forum, but I have another idea also.
Feel free to take a look at the power supply schematic while I do some investigation and testing myself. :)
Seekonk:
Should work if you pull the batteries and place a 4700uF cap in its place. Interesting design, what size uf is C201? That might have to be increased with an additional parallel cap. Watch how hot the zener gets, especially OFF. Might want to disconnect the OFF winding of the transformer. Do some tests and report back.
xrunner:
--- Quote from: Seekonk on March 13, 2015, 03:59:30 pm ---Should work if you pull the batteries and place a 4700uF cap in its place.
--- End quote ---
It might at that, but I'm still keen on another idea. :)
--- Quote --- Interesting design, what size uf is C201? That might have to be increased with an additional parallel cap.
--- End quote ---
It's 5 uF. According to the manual it's a cap that has to be changed out depending on the operating voltage and line freq. , of course it's the correct one for 120V - 60 Hz, but I may not have to worry about it if my idea pans out.
--- Quote ---Watch how hot the zener gets, especially OFF. Might want to disconnect the OFF winding of the transformer. Do some tests and report back.
--- End quote ---
I'm testing my idea this afternoon, will report back ... 8)
Seekonk:
If you notice there is no dropping resistor for the zener that prevents over voltage to the batteries. The 5uf capacitor performs that function of the voltage drop, that is the simplistic explanation. You have to be careful with capacitors in series with inductors. I have these nice German fans that are 220V. To use them on 120V I place a 4uF in series and that gives me 190V on the motor because the RL is nearing resonance which will cause the highest voltage on the inductor and capacitor in series. Note also when the unit is off it switches to a higher winding to charge because there is no current draw from the meter electronics. I would disconnect that winding if is going to be plugged in all the time.
SeanB:
Replace CR22 with a 5V1 25W zener on a smallish heatsink, so that it provides the required 5V rail. Parallel a 1000uF 25V capacitor across it as well, and remove CR21 and CR23 as well, and disconnect the red terminal on the transformer. Place a 120V MOV across red and black on the transformer primary, this will help with high voltage spikes.
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