Author Topic: Fluke 8600A Battery / Power Supply Conversion  (Read 8470 times)

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Offline xrunner

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Fluke 8600A Battery / Power Supply Conversion
« on: March 13, 2015, 03:43:15 pm »
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.  :)







My friends say they're procrastinators. I say I've been meaning to tell them for years, but I just keep putting it off.
 

Offline Seekonk

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #1 on: March 13, 2015, 03:59:30 pm »
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.
« Last Edit: March 13, 2015, 04:01:02 pm by Seekonk »
 

Offline xrunner

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #2 on: March 13, 2015, 06:40:37 pm »
Should work if you pull the batteries and place a 4700uF cap in its place.

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. 

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.

I'm testing my idea this afternoon, will report back ...  8)
My friends say they're procrastinators. I say I've been meaning to tell them for years, but I just keep putting it off.
 

Offline Seekonk

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #3 on: March 13, 2015, 09:30:56 pm »
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.
 

Offline SeanB

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #4 on: March 14, 2015, 08:23:08 am »
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.
 

Offline xrunner

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #5 on: March 14, 2015, 02:08:46 pm »
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,...

Thanks for the idea. Here's what I've done: I, of course, had it disconnected from the mains. I then removed all the batteries, which were turned in for recycling at Home Depot. I then simply connected a bench PS set to 5V to the appropriate terminals on the board and the meter worked perfectly. I noted that the current draw was 430 mA. So this tells me which direction I want to go. It's favorable to my initial idea.  :)







My friends say they're procrastinators. I say I've been meaning to tell them for years, but I just keep putting it off.
 

Offline SeanB

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #6 on: March 14, 2015, 02:33:04 pm »
That is only if you are not willing to remoce CR22, replace it with a 1000uF 25V capacitor and then snip one lead of L2 and place a 7805 on a heatsink in series with the lead, and with the case connected to the common of the power supply on the transformer yellow lead. Then you can leave the primary side as is, and it will have a regulated 5V rail and a lower power draw from the mains to boot.
 

Offline edavid

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #7 on: March 14, 2015, 02:37:17 pm »
Should work if you pull the batteries and place a 4700uF cap in its place.

This is incorrect, you also need a regulator.  A Chinese "LM2596" stepdown module should work well.
 

Offline SeanB

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #8 on: March 14, 2015, 02:41:42 pm »
Should work if you pull the batteries and place a 4700uF cap in its place.

This is incorrect, you also need a regulator.  A Chinese "LM2596" stepdown module should work well.

There is a zener regulator in there, CR22, but I am wary of running it at 400mA of current, as it probably is a 1W zener. It will probably go short circuit after a while, but if it goes open circuit bye bye meter.
 

Offline edavid

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #9 on: March 14, 2015, 02:53:26 pm »
Should work if you pull the batteries and place a 4700uF cap in its place.

This is incorrect, you also need a regulator.  A Chinese "LM2596" stepdown module should work well.

There is a zener regulator in there, CR22, but I am wary of running it at 400mA of current, as it probably is a 1W zener. It will probably go short circuit after a while, but if it goes open circuit bye bye meter.

The manual says that CR22 is a UZ8720 20V 1W zener.  The supply voltage goes up to 7-8V without batteries, which is not fatal, but not so great either.  As I said, add a regulator.
 

Offline xrunner

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #10 on: March 14, 2015, 10:17:18 pm »
The solution I'm going to use is coming out of this box, but there's more to it than just soldering up a couple of wires.  8)

My friends say they're procrastinators. I say I've been meaning to tell them for years, but I just keep putting it off.
 

Offline edavid

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #11 on: March 14, 2015, 10:22:53 pm »
The solution I'm going to use is coming out of this box, but there's more to it than just soldering up a couple of wires.  8)

The trouble with that is that some of the 8600A DC-DC converter modules are not really happy at 5.0V, they need 5.5V or so.
 

Offline xrunner

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #12 on: March 15, 2015, 12:26:51 am »
The trouble with that is that some of the 8600A DC-DC converter modules are not really happy at 5.0V, they need 5.5V or so.

Oh I already checked it out with 5V from my bench supply - it's happy.  ;)

But I have found a candidate. I've patched it in and the meter works perfectly. I'm going to integrate the little board into the meter, this is just a test. The little switcher can handle 700 mA A. It ran all afternoon with no problems at all. The meter will still use the same line cord as usual.

My friends say they're procrastinators. I say I've been meaning to tell them for years, but I just keep putting it off.
 

Offline xrunner

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #13 on: March 15, 2015, 05:33:34 pm »
I removed the little supply from it's "wart" and will be mounting it inside the meter along with the mounting parts for the batteries, so as to keep all the original parts inside. It turns out I have to do little to make this work. First off I'm pulling the input wires for the transformer and bundling them inside some heat shrink - they will be unused. The mods I'm making are shown in the schematic.





My friends say they're procrastinators. I say I've been meaning to tell them for years, but I just keep putting it off.
 

Offline SeanB

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #14 on: March 15, 2015, 05:37:16 pm »
Add the optional MOV to that little board, it will help it last longer.
 

Offline Seekonk

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #15 on: March 15, 2015, 05:41:36 pm »
Good refurb. I think you made the best decision.  I thought about the many ways to convert this Li batteries if it were mine since I have stacks of used batteries.  This is a good bench meter, but too clunky these days to take out in the field.
 

Offline xrunner

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #16 on: March 15, 2015, 05:58:51 pm »
Add the optional MOV to that little board, it will help it last longer.

OK good idea.

Good refurb. I think you made the best decision.  I thought about the many ways to convert this Li batteries if it were mine since I have stacks of used batteries.  This is a good bench meter, but too clunky these days to take out in the field.

Thanks, yea these days who would drag that into the field with batteries - the thing was pretty heavy with all those D cell NiCads. But it's a really good bench meter so why not convert it? I was very surprised when I got this one because it's so clean. The inside looks like it just came off the factory floor. On the top back it has "USN" stenciled on it, but I would never have believed it was in the possession of the Navy. It's just not been abused at all. Well, except for the V-ohn and common jacks. The inside is so worn the banana plugs do not fit in at all tightly anymore. I'm going to change them out with new ones. Maybe it was in some lab for years and just sat on a bench, someone plugging and unplugging various things?  :-//
My friends say they're procrastinators. I say I've been meaning to tell them for years, but I just keep putting it off.
 

Offline Seekonk

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #17 on: March 15, 2015, 09:01:43 pm »
Since you have a stack of wall warts, it is easy to change the voltage up to several volts.  That opto isolator likely has a zener in series in which case a diode or two in series will bump it up a little.  OR they have a TL431 that gives you lots of options for voltage.

Some here talk about crappy wall warts cause they draw half the rated current and the voltage drops.  Look for a resistor on the output that is a current sense feeding a transistor to the opto.  Remember, most of these are chargers and they limit the output in the case of dead or damaged batteries.

I do a lot with solar and many of these modules will work down to 50V at reduced current.  Nice for an isolated high side driver or operating a micro.
 

Offline xrunner

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Re: Fluke 8600A Battery / Power Supply Conversion
« Reply #18 on: March 16, 2015, 02:08:08 pm »
So here is the final installation. I kept all the holder parts for the NiCads, and used one of them to hold the PS board off the circuit board

I also needed to replace the banana jacks on the fromt due to extreme wear, so I disassembled the instrument and pulled the front panel so I can replace the jacks and re-work the wiring to them.












My friends say they're procrastinators. I say I've been meaning to tell them for years, but I just keep putting it off.
 


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