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 2.GQ Geiger Muller Counter
 GMC-500Plus support 18650 LiFePO4 Batteries?
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Tuser55

4 Posts

Posted - 05/15/2022 :  04:25:29  Show Profile  Reply with Quote
Simple question does the GMC-500Plus support 18650 LiFePO4 Batteries?

Was just curious because LiFePO4 have a long life (5-10 years) and in my case it seems like it would be a good fit. I only use my GMC-500Plus a few times a year so I wouldn't have to worry about having to change the 18650 Lithium battery every other year.
Reply #1

Damien68

France
703 Posts

Posted - 05/15/2022 :  09:33:50  Show Profile  Reply with Quote
I don't think you should do that at all.
charging end voltage of LiFePO4 is 3v65
charging end voltage of standard LiPo is 4v2
so, if you charge a LiFePO4 battery with a device made for LiPo maybe it can explode, in all case is not optimal.
The original battery lasts a long time.

Mastery is acquired by studying, with it everything becomes simple

Edited by - Damien68 on 05/16/2022 22:56:05
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Reply #2

ullix

Germany
800 Posts

Posted - 05/16/2022 :  20:30:54  Show Profile  Reply with Quote
The switch to LFP (LiFePO4) batteries is an interesting idea, but for a different reason than longevity.

I am using a number of the "old" 18650 Li-Ion batteries for several years now, and they still work ok. Changing every year is surely not required.

However, the "old" Li-Ion batteries occasionally go up in flames, which is really inconvenient for users of electric-cars, electric-buses, electric-motorbikes, laptops, and more.

It may give a strong hint that Tesla is now changing their batteries towards LFP! And this despite the fact that LFP has a somewhat lower energy capacity.

Fortunately, the GMC counters are rather benign with respect to their power usage, so that would be ok. If you really need more capacity, take an extra Powerbar with you.

But knowing that GMC counters don't have to be added to the list of exploding devices may be a really good thing!

Compared to the "old" Li-Ion batteries with a nominal 3.7V, the LFP type has only 3.2V. It surely won't hurt anything expecting 3.7V, but whether it suffices to operate it is a different question. I hope that @EmfDev can tell us?

@Tuser55: Are you sure to have a LFP battery? Could you measure and tell us the voltage of your fully charged, unconnected battery?


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Reply #3

Tuser55

4 Posts

Posted - 05/17/2022 :  04:29:16  Show Profile  Reply with Quote
@ullix

The only reason why I'm interested in LFP batteries is because I bought the GMC-500 Plus just for scientific reasons and to also add to a Home Disaster Supply Kit so I don't really use it that much. I like the idea of using LFP batteries because of their long life. So if something ever happened I don't have to worry about going to get the meter and then finding out that the batteries don't work because the meter has been idle for so long.

The voltage of my regular 18650 Li-Ion is about 4.2 volts when fully charged. So it appears that the charge controller in the GMC-500 Plus considers a battery fully charged at around 4.2 volts. So it would probably be a bad idea to put a 18650 LFP battery into the GMC-500 to charge it.

But what if you just put a LFP battery in the GMC-500 and disabled charging would the device turn on or would the lower 3.2 volts coming out of the battery damage it? Or could you change the max charge voltage in the GMC-500 plus from 4.2V to 3.6V?
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Reply #4

Damien68

France
703 Posts

Posted - 05/17/2022 :  06:50:41  Show Profile  Reply with Quote
@Tuser55:
it is true that it is recommended to recharge unused device embededing LiPo batteries at least once a year. what would be critical would be for auto-discharge bring Battery voltage below 2v8 which could render Battery permanently unusable.


personaly I also use the 18650 in my flashlight which I use a lot in the winter. so I have an external charger and 2 extra batteries that I keep charged.

Mastery is acquired by studying, with it everything becomes simple

Edited by - Damien68 on 05/17/2022 07:20:04
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Reply #5

Tuser55

4 Posts

Posted - 05/17/2022 :  08:24:06  Show Profile  Reply with Quote
quote:
Originally posted by Damien68

@Tuser55:
it is true that it is recommended to recharge unused device embededing LiPo batteries at least once a year. what would be critical would be for auto-discharge bring Battery voltage below 2v8 which could render Battery permanently unusable.


personaly I also use the 18650 in my flashlight which I use a lot in the winter. so I have an external charger and 2 extra batteries that I keep charged.



The other advantage to LFP batteries is leaving the battery at 100 % all the time doesn't cause the battery capacity to degrade as much unlike Li-Ion. I have read that a fully charged lithium-ion battery will lose about 20 percent of its capacity after a year of typical storage.
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Reply #6

Damien68

France
703 Posts

Posted - 05/17/2022 :  08:55:24  Show Profile  Reply with Quote
yes it is also the data that I have, a battery in the device will discharge a little faster because even turned off the device will consume a little current (even if it is very little it is not zero). recharging "every year" is a precautionary measure.

I don't work for GQ, but inside my GMC-500+ there is a linear regulator to make 3v3 to power the circuits, I think the LFP voltage will be too low to make the device work properly.

Mastery is acquired by studying, with it everything becomes simple
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Reply #7

ullix

Germany
800 Posts

Posted - 05/17/2022 :  21:54:21  Show Profile  Reply with Quote
@Tuser55: If you think of having that rare usage of a Geiger counter, wouldn't regular alkaline batteries be even better than rechargeables?

An alkaline at 1.5V times 3 gives 4.5V, and this is very close to the 4.2V max of an Li-Ion battery (Actually, this nomenclature is misleading: all the rechargeable batteries under consideration are Li-Ion based. This type is a NMC-type battery, as opposed to the LFP-type battery, not to mention the many other variants.)

Changing from NMC to LFP would probably require several changes to the GMC counter. Given the charge/discharge profile https://de.wikipedia.org/wiki/Lithium-Eisenphosphat-Akkumulator#/media/Datei:LIFePO4_charge_discharge_diagram.svg a buck-boost converter may be required to reach the 3.3V. But the you could take 2 of them in series and were closer to the USB voltage, but perhaps charging for serially connected batts would become a bit more demanding.

At the end the added safety from LFP would be a selling point for me. Imagine the headline "Scientist investigating Chernobyl reactor in ware torn Ukraine dies from a battery explosion of his Geiger counter" ;-)





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Reply #8

ullix

Germany
800 Posts

Posted - 05/17/2022 :  22:07:31  Show Profile  Reply with Quote
I just opened the case of a GMC300E+ and found the microcomputer STC15L2K60S2. I googled the datasheet "STC15series MCU Data Sheet" and found this entry (page 15):

quote:
Operating voltage range:
STC15L2K60S2 series: 3.6V ~ 2.4V (3V MCU).


Compared with Wikis Charge/Discharge profile, this looks like a match made in heaven:




Am I missing anything?
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Reply #9

Damien68

France
703 Posts

Posted - 05/17/2022 :  23:12:58  Show Profile  Reply with Quote
I just tested my old GMC-500+ with a laboratory power supply,
it works down to 2v8 - 3v.

at 2v8 it indicates battery low and shuts down
at 2v9 - 3v it works

as soon as the voltage drops below 3v3 the voltage for the tube will drop. if set to 400v at 3v3 or more, at 3v theoretically there will only be around 364v
400v * (3v/3.3v)) = 364v.

and 340v at 2v8.

also i think its better to use a LiPo than LiFePO4

Mastery is acquired by studying, with it everything becomes simple

Edited by - Damien68 on 05/17/2022 23:17:26
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Reply #10

Tuser55

4 Posts

Posted - 05/18/2022 :  06:44:23  Show Profile  Reply with Quote
quote:
Originally posted by Damien68

I just tested my old GMC-500+ with a laboratory power supply,
it works down to 2v8 - 3v.

at 2v8 it indicates battery low and shuts down
at 2v9 - 3v it works

as soon as the voltage drops below 3v3 the voltage for the tube will drop. if set to 400v at 3v3 or more, at 3v theoretically there will only be around 364v
400v * (3v/3.3v)) = 364v.

and 340v at 2v8.

also i think its better to use a LiPo than LiFePO4



Good to know thanks

Edited by - Tuser55 on 05/18/2022 06:45:23
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Reply #11

ullix

Germany
800 Posts

Posted - 05/18/2022 :  22:36:50  Show Profile  Reply with Quote
So the microchip seems indeed to be ok at these low voltages.

For the anode voltage I am not sure how to interpret your data: it looks like the anode voltage is not measured, but guesstimated from some setting? That would imply that it can be increased to desired voltage by simply increasing that ominous setting?
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