Charger advice for 18 volt NIMH battery packs?

[grand-moff-tarken]

Thanks amberwolf

Yeah, it had not occurred to me until yesterday that maybe the cells themselves are not exactly what they seem (or were advertised to be). I have continued my charge/discharge experiments, and the highest capacity I've hit so far is 1251 mAh....a far cry from the advertised 4800 mAh. I just ordered the correct temperature sensor, so I'll be able to monitor the actual temperature as opposed to just feeling the outside casing with my hand. Ultimately, if the performance continues to be this low, I'll just return them and buy something else (maybe LiON packs, if not too expensive).

FYI - I am not shutting down the charge myself when it reaches a particular target voltage. Rather I am letting the Tenergy unit shut the charge cycle down when it senses the voltage drop (that's what the "NiMH sensitivity" mV number is all about). The unit has four safety features you can enable to avoid overcharging or overheating: mV drop sensitivity, total capacity delivered, overall time and the temperature probe (you can choose which ones to turn on or off). Right now, I am using three of them (everything except the temp probe), and I presume it is the mV drop that's shutting the charge cycle down (it never even gets close on the overall time or capacity settings). I will take your advise, however, and try some "temperature-only" charge cycles once I get the temp probe.

I must say it's been very interesting using the Tenergy unit, if only to monitor the mAh quantity either absorbed or discharged on each cycle. If you don't have an instrument like that available, I guess you'll never really know how close to the advertised capacity your batteries are getting!

Thanks very much again for your time and advice. I will continue to post any new findings or updates here

 

[amberwolf]

Yeah, it had not occurred to me until yesterday that maybe the cells themselves are not exactly what they seem (or were advertised to be).

It is unfortunately extremely common.

there are even cases where an 18650 / etc shell is used and a tiny "chiclet" cell is installed inside. Seems liek a huge waste of time to me, but it must be profitable as it has been done by more than one "company".

Other cases simply fill empty shells with sand / etc to give the right weight (like that is going to fool someone into thinking they have real cells, when there is no voltage, etc)

Others simply create fake labels or wrappers for cells. Some of those are ridiculously impossilbe, like 100,000Ah on an 18650 :lol: , some of them are plausible but are fake for the cell they're on, taking low-capacity cells and remarking them as high capacity ones. Then there are places like the various *fire companies and more than a few "blue block" battery sellers that have been known to use literal recycled garbage cells from random scrapped packs, and not only rewrap them (often with impossible capacities) but recap the ends to cover the old spot welds.

Most of those are examples with Lithium cells, but there's no exclusivity of chemistry in the counterfeit industry. :/

Pretty much nothing can be done about it other than knowing it's a problem and avoiding any seller except those that you know for sure don't carry such garbage.

I have continued my charge/discharge experiments, and the highest capacity I've hit so far is 1251 mAh....a far cry from the advertised 4800 mAh. I just ordered the correct temperature sensor, so I'll be able to monitor the actual temperature as opposed to just feeling the outside casing with my hand. Ultimately, if the performance continues to be this low, I'll just return them and buy something else (maybe LiON packs, if not too expensive).

As long as you pick reputable ones, either one should be ok. You can probably get about hte same capcity from either one, and potentially the same discharge rate.

But if you need to be able to charge the packs and leave them charged for more than a few hours to a day and still have the full capacity present, Nickel cells are a poor choice; with high self discharge. They're fine if you need to charge them right before using them, but otherwise you're better off with a lithium variant.

If you're only using htem for hte power tools, getting good-quality compatible toolpacks is your best bet, but if you also need them for other things you might consider some other pack type with an extension cable / adapter to a toolpack housing (from your old packs, for example), if that is a possible use case for your tools.

FYI - I am not shutting down the charge myself when it reaches a particular target voltage. Rather I am letting the Tenergy unit shut the charge cycle down when it senses the voltage drop (that's what the "NiMH sensitivity" mV number is all about). The unit has four safety features you can enable to avoid overcharging or overheating: mV drop sensitivity, total capacity delivered, overall time and the temperature probe (you can choose which ones to turn on or off). Right now, I am using three of them (everything except the temp probe), and I presume it is the mV drop that's shutting the charge cycle down (it never even gets close on the overall time or capacity settings). I will take your advise, however, and try some "temperature-only" charge cycles once I get the temp probe.

Personaly I expect it won't change, and that you've just got counterfeit packs.

I must say it's been very interesting using the Tenergy unit, if only to monitor the mAh quantity either absorbed or discharged on each cycle. If you don't have an instrument like that available, I guess you'll never really know how close to the advertised capacity your batteries are getting!

It's interesting to be able to test things this way; I used to gather such data on most of my battery powered devices for curiosity, until I began to get a "feel" for each one, and then spent the time on other experiments instead.

Your Tenergy unit is much more advanced than mine was--mine didn't even have a display, just a switch between a couple of functions, IIRC.

One of the more useful such devices I have is an Atorch USB power meter, which comes iwth standard USB on each end and cables to give you other ends including alligator clips for various things. Has been useful for a number of things, including even just testing how much power various USB and other DC-powered devices require along with how much voltage sag occurs at various loading of their supplies.

I've also used typcal RC hobby chargers that can deal with several chemistries, and also have a Cycle Satiator from ebikes.ca that is programmable for a variety of uses (not quite as versatile as the hobby chargers, but vehicle-mountable and fairly environmentally-sealed).

 

[marty]

I'll just return them

I can imagine dumpsters of returned junk at Walmart and Amazon. Saw a sign at a wholesale plumbing supply place.

BOUGHT SOMETHING YOU DON'T WANT?
NOW YOU GOT ONE IN CASE YOU EVER NEED IT

You got a bunch of functional battery cases. Put junk battery cells in the hazardous waste pile. Buy a spot welder. Buy some new battery cells from a REPUTABLE battery supplier. Pretend you are building a electric boat to cross the Atlantic Ocean. Important to have quality battery cells so you don't become stranded in the middle of the ocean.

Where to find a REPUTABLE battery supplier? Don't even think about Amazon and Walmart. I don't know any REPUTABLE battery suppliers. Maybe try the internet? REPUTABLE battery supplier.

Now lets get back to the boat. Want to travel from Buffalo NY to Mediterranean Sea.