Fluke 123 Battery Modification?

[Gokhan]

I bought a Fluke 123 last year and i love the quality, screen and the scope function.
Despite all that, i hate the battery. It takes ages to charge and quickly drained.
A new battery is around 40 usd from china but i have seen a few post about modded fluke 123 with 18650 cells.

Anyone who tried and can tell me, advantages? Are you still happy about it?

Attaches are the mod, i have found. What about the termistor and resistor on the original package? not gonna use anymore?

[J-R]

I can't speak to the modification directly.  This is your first post so I don't have any data to determine your skill level, but making modifications to this relatively expensive ($500+) device would be a last resort in my opinion.  There are chances for mistakes or odd behavior.
At least here in the US, Tenergy's eBay store has been my go-to for cheap replacement NiCd & NiMH: https://www.ebay.com/str/tenergy
A lot of their batteries can be purchased with tabs, which means you could solder up a pack with minimal effort, as opposed to having to spot weld the pack together.
So buying bare cells and building your own pack might be cheaper, although $40 for a ready-made one seems attractive.

[robert.rozee]

i'd be very reluctant to modify any charging circuitry designed for Ni-Cad and/or Ni-Mh cells to instead try and charge Li-Ion cells. while the older technologies are relatively forgiving over how charging is carried out, Li-Ion is not and you may well end up overheating the cells during charging and even causing them to explode/catch fire.

A far better approach would be to create some sort of external battery pack that: (a) can only supply power to the Fluke 123 and not be capable of receiving charge from it, and (b) contains its own separate charging circuitry that can be used to charge up the Li-Ion batteries within. Note that this would very much violate the electrical isolation afforded by the Fluke 123 design, but then you could (as J-R points out) also rebuild a battery pack using tabbed Ni-Mh cells that you keep for use just on those occasions when electrical isolation matters.


cheers,
rob  :-)

[Gokhan]

Thanks for reply

I have the necessary equipment and skills, so its kinda easy fix, im just currious about the if it will damage the fluke over time

[robert.rozee]

i was rather hoping someone else would step in and comment, but it seems not.

Ni-Mh cells are charged with a constant current. end-of-charge is sensed by a small drop in cell terminal voltage. once fully charged they can be kept 'topped up' with a small trickle charge of less than 1/20th C.

Li-Ion cells are charged with a current-limited constant voltage. during the initial stage of charging the cell voltage will rise from 3.0 volts (discharged) to 4.2 volts (partially charged); the current has to be limited by the charging circuit to something between 1C and 1/4 C. once the cell voltage has reached the 4.2 volt limit the remainder of charging occurs with charging current tapering off and is usually terminated when it drops down to 1/10th of the initial current limit.

if a Li-Ion cell has a voltage significantly less than 3.0 volts it is usually unrecoverable. the charging circuitry should detect this and stop - although occasionally a cell can be brought up to 3.0 volts with a small trickle charge, after which the cell may sometimes be partially functional (for example, having a reduced capacity).

both schemes may have temperature sensors on the cells, along with safety timeouts.


while both schemes are relatively simple, they are very different. trying to charge Li-Ion cells with the Ni-Mh charging scheme will result in a bad outcome. trying to charge a Ni-Mh cell with the Li-Ion scheme will likely result in the charging circuit detecting a fault and shutting down.

you are unlikely to have much long-term success adapting a Ni-Mh charging circuit to work with Li-Ion cells. you will be able to get some charge into the Li-Ion cells, but not in a way that is reliable and safe. you definitely will not be able to safely leave things charging overnight while unattended.

as i suggested before, you would be better off putting Ni-Mh cells back into the Fluke 123 and then creating an external Li-Ion pack that has its own charging circuitry that operates independently from the Fluke 123.


cheers,
rob   :-)

[daisizhou]

Did the Fluke 123 originally use lithium batteries or NiMH or NiCd batteries?

I didn't find any special chip for battery management.I remember that the most commonly used chips are TI's BQ series chips, but I didn't find any similar chips in your pictures.

[robert.rozee]

Did the Fluke 123 originally use lithium batteries or NiMH or NiCd batteries?

according to Fluke's website, at least some of the 120 series originally came with Ni-Cd, and a Ni-Mh was available as a retrofit for all:
https://www.fluke.com/en/product/accessories/batteries/fluke-bp120mh


cheers,
rob   :-)

[Gokhan]

Thank you for your answer.

Maybe i should stick with a new battery from china to see how long it will last and i will also keep my fluke as genuine as possible

[AVGresponding]

While I'd agree it's not viable to use the existing charge circuit, even with modifications, with a Li-ion battery, I do use a home-made LiFePO4S 2-cell pack in my 99B S2; I do not charge it in situ, I take it out for that. I also use separate connectors on the pack for charger and load, in order to implement series diode protection for both. Works pretty well.

Haven't done Terra's modded battery packs for my Tek THS scopes yet...   

[BeBuLamar]

Thank you for your answer.

Maybe i should stick with a new battery from china to see how long it will last and i will also keep my fluke as genuine as possible

I had a Fluke 192C at work and with brand new genuine battery from Fluke it doesn't last that long and I almost always have to use it with the AC adapter plugged in. I would use Li-Ion or LiFePo4 battery. Just modify the battery pack not the scope. Charge the battery with another charger outside of the scope.

[Gokhan]

Thank you all for your responses.
I ordered a new battery for 35 dollar locally, let see how long it will last.