Fluke 8600A Fault

[PE9ZZ_JO22KI]

In the battery-only version there's no reservoir capacitor in the battery charger. If you add one it may blow up the power supply. If you feed +5 V (China wall wart) into it it should work just fine.

Incidentally, found the manual at Mrs. Tanya (or is it Miss?).

Tjerk, 9ZZ

[neutronic]

Originally Posted by Paul Erickson

Has anyone replaced the battery supply with an AC only supply? From searches I see that running this without the batteries does not work.

You can do this only once!
Then it is over.
It kills a lot of unobtainable IC´s
I know,because I learned the hard way.

Jard N

[Paul Erickson]

Thanks for the replies everyone. I understand that running the current power supply without the batteries is going to fail. I was just wondering if anyone had replicated the original mains circuit using the Fluke configuration. Comparing the two different versions, the parts count is low for the AC only supply, but replacing the transformer may take a bit of doing. I'm wondering what would be more cost effective, replacing the batteries with new ones, or replacing the power supply.

What else am I missing here?

[Leon Crampin]

Just fit 4 good "D" cells with clean contacts. I used an 8600A extensively for field work in the '70s and it served me well.

The only problem I had with the 8600A was that unlike the 8000A, there was no visual indication that it was charging. A dead socket in a hotel room once caused wasted time on the job on the following day.

Leon.

[PETERg0rsq]

4 good D-Cell NiCad's will probably cost more than the meter is worth!!!! (£8 per cell last time i tried to get some)

The charging circuit would destroy NiMh in a very short time!

A cheap walwart adaptor could be purchased for about £5, or a decent homebrew linear for a little more.

I have several of these meters, and replace the D-Cells with a D-Cell adaptor which holds two AA Nicads, which can still be found for decent prices.

These regulate and smooth out the AC supply well, with the added advantage of short term portable use (1 hour).

peter

[Alistair D]

D size NiCad packs are still used in emergency lighting units. 5 and 6 cell packs can be found on Ebay for around £10. I cannot vouch for the quality and age of these batteries or even how easy it would be to split them apart to make new combinations but would be worth a punt.

Al

[Paul Erickson]

Originally Posted by PETERg0rsq

The charging circuit would destroy NiMh in a very short time!

Thanks Peter,

How difficult would it be to modify the charger circuit to accommodate NiMh cells?

cheers, Paul

[cmjones01]

Originally Posted by Paul Erickson

How difficult would it be to modify the charger circuit to acommodate NiMh cells?

Pretty tricky - the charge circuit relies on NiCd batteries' ability to be trickle-charged more or less indefinitely without damage. That means it doesn't need, and doesn't have, any way of telling when the batteries are full. It just leaves them connected, and charging, all the time the mains is connected.

Unfortunately NiMH batteries can't be charged this way. They don't like being trickle-charged to more than their capacity, so the charger needs to be able to detect when the battery is fully charged. This isn't trivial with NiMH batteries: you either have to detect the rise in temperature of the battery, or spot that its terminal voltage has started to fall slightly. If the charger doesn't do this, the batteries will just sit there getting hot and they will cease to be batteries pretty quickly. Modifying the Fluke circuit to spot this end-of-charge is a big job.

Chris

[Paul Erickson]

Originally Posted by PETERg0rsq

I have several of these meters, and replace the D-Cells with a D-Cell adaptor which holds two AA Nicads, which can still be found for decent prices.

Thanks Peter,

Would you happen to have a picture of the D-Cell adaptors you are referring to?
I can find plenty but none with the tabs necessary to mount in the meter. Or, are
you using some other means to connect them?

Thanks again for the time and attention.

cheers, Paul

[Paul Erickson]

Originally Posted by cmjones01

Unfortunately NiMH batteries can't be charged this way. They don't like being trickle-charged to more than their capacity, so the charger needs to be able to detect when the battery is fully charged. This isn't trivial with NiMH batteries: you either have to detect the rise in temperature of the battery, or spot that its terminal voltage has started to fall slightly. If the charger doesn't do this, the batteries will just sit there getting hot and they will cease to be batteries pretty quickly. Modifying the Fluke circuit to spot this end-of-charge is a big job.

Thanks Chris,

I was wondering if any of the available smart NiMH charger chips would be suitable in this application. Must confess I am intrigued about the possibility, but also conscious that this project is probably getting to be more complicated than it is worth. If I can find the adapters Peter is referring to, will probably go that route.

Thanks again.

cheers, Paul

[cmjones01]

Originally Posted by Paul Erickson

I was wondering if any of the available smart NiMH charger chips would be suitable in this application. Must confess I am intrigued about the possibility, but also conscious that this project is probably getting to be more complicated than it is worth. . . If I can find the adapters Peter is refering to, will probably go that route.

I'm sure smart charger chips could be used, but you'd also have to change the whole power supply arrangement in the Fluke to suit. The existing design effectively uses the battery as part of the power supply regulator, so if you change the way the battery is handled, you're redesigning the whole power supply from scratch. Probably not worth it. If I were going to do it, I'd probably just rebuild the power supply to be a mains-only 'battery eliminator' and have done with it. I don't think the battery-powered capability of the 8600A is really worth trying to use these days: a more modern LCD 4.5 digit multimeter, if you need that much precision, would simply do just as good a job for a lot less trouble.

I've got a whole load of 8600As in frequent use and I'm fond of them, but they do their jobs tethered to the workbench.

Chris

[PETERg0rsq]

Originally Posted by Paul Erickson

Would you happen to have a picture of the D-Cell adaptors you are refering to?
I can find plenty but none with the tabs necessary to mount in the meter. Or, are you using some other means to connect them?

Here are some pictures of the adapters and the batteries i chose,.

Also a picture showing them installed in the meter.

No need for any tabs!

I did originally try cutting open some emergency lighting D-Cell packs, but they don't split!! The ones I had are three D-Cells fabricated in a single tube!
Like three cells in a car battery in a single case.

I tried splitting them, but it destroyed the cells.

Peter

[Paul Erickson]

Thanks Peter. I see now what you mean, but am wondering the source of the metal contact strips you show in the second picture. The dead batteries in my meter had tabs, so if the contact pieces are part of the original setup, I don't have them.

Paul

[PETERg0rsq]

My meter is standard, no mods!

I have four of these, and they were designed to take regular D-Cell nicads.

The Metal tags are soldered to the pcb, and pass through the two battery clamps, which hold them tight against the batteries.

I have four of these meters and they are all the same (and another 6 in the garage waiting to be looked at!!!)

Do you still have the battery clamps, or were these removed also?

Maybe yours is an earlier or later version, and fluke changed the design?

Peter

[PETERg0rsq]

Paul

Just had a look in one of my battery Fluke 8000 DMM's (very similar to an 8600, but only 3.5 digit) with a smashed case (I was looking at removing the parts you needed) and noticed that this uses tagged D-Cells, as you describe.

Looks like there ARE at least two different variations.

So I will need to look for a similar solution as you are looking for.

Fortunately the battery holding clamps still used, so securing the batteries is not a problem.

I think I will be looking at a similar solution using the D-Cell adapters, and soldering flying leads to them.

Peter

[Paul Erickson]

Peter,

Thanks again for all the help. Yes, the battery holders are in place. I don't know if the meter originally came with tabed batteries of they were a subsequent repair/modification. I have a set of D-Cell NiCd with tabs enroute. Will try those and see how long the batteries last. If you come across a source for the contact strips please let me know, because I like your solution better for the long run.

Thanks again.

cheers, Paul