What to do with these used 18650 Ni-MH ?

[ichiban]

A friend of mine has a few hundred of salvaged 18650-format of Nickel Metal Hydride cells (I guess - never saw this size before). He asked me how can he re-use them ?

I measured each cell of 1.3xx V. and the whole 10S1P pack is 13.xx V. I heard that they were from old medical equipment as a back-up power. They are still in good shape and I doubt they have been through 50-100 cycles usages max. With 4500mAh markings on the wrap, that means 4.5Ah * 1.3V = 5.85Wh which is low. About half of our generic Li-Ion cells at best. So e-bike batt might not be appropriate since their power density are very low, ending up in very large pack and heavy.

What should one re-purpose them into ?















See the 18650 Li-Ion cell I place next to the 10S pack above.

 

[amberwolf]

Stationary power sources of various kinds.

Powerwalls, either powering an AC inverter, or directly setup for powering DC devices that can operate from whichever voltage range(s) the cells can be configured into.


DC example: if one has battery-operated powertools that are only used inside a shop, always on , for instance, one could make a stationary pack with these that uses a (retractable?) cord to an adapter pack that connects to the tool(s). Not much reason to do this for tools that have working packs, or that you can still get new packs for, but if you have old tools that you'd have to build batteries for....


Or certain short-run high-current weight-unimportant devices, like a lawnmower: If you have an old SLA mower that needs a new battery, these are probably at least as power/energy dense as SLA.

Solar powered lighting: If they'll fit in the enclosure, or you can make one, you can replace old batteries in small lighting units.

I'm sure there's a bunch of things I didn't think of.

 

[ichiban]

Thanks amberwolf, appreciate your feedback. I agree with you for the applications for Ni-MH's repurposing.

There is nothing wrong with Ni-MH, IMO. I believe many of us had good experience with them before. But when the new-kid-on-the-block Lithium arrived, uncle NiMH inevitably faded out. Hardly hear about grandpa NiCd nowaday.

For these 4500mAh Ni-MH packs above, I found some info on the net which is not exactly but likely be close. I learned that they are not 18650 format but just a few mm longer. D18-mm * L67.5-mm. See attached.

I also notice that there is no single BMS within these 10S packs. There is only 1 thermal fuse on each pack. That probably means :

a) The termal fuse is the only protection they have from cells heat : short-cct, overloaded, overcharged, overdischarged, etc. Balancing is not as important. So, one can drain the Ni-MH pack down to zero ≈ premature death.

b) Since Ni-MH's era were in quite early stage of portable power devices/equipment. Very little large packs uses in EVs, ebikes popularity like now. So people still did not know/care much about Ni-MH balancing that such process can prolong/ensure longevity/safety of the pack. Lithium are more sensitive and quite expensive so people need to get the most cycles out of them ?

Also that little (or none reported) accidents/incidents, unlike Lithium packs' scary public image. But I never had any serious issue with my Li packs before, after about 1,000 cycles to-date.

I heard that Toyota and few more manufacturers still use Ni-MH in their hybrid cars until now. Do not know what spec of their packs/cells. So there are still some Ni-MH in the market waiting to be re-purposed for other purposes as well.


FDK HR-4/3FAU 1.2V 4500mAh NIMH battery 4/3FA
Spec and picture from : https://www.keeppower.com.cn/products_detail.php?id=404

1. Model: FDK HR-4/3FAU 1.2V 4/3fa nimh battery
2. Type: Nickel-Metal Hydride Battery
3. Size: 4/3FA
4. Typical Capacity: 4500mAh
5. Minimum Capacity: 4100mAh
6. Nominal Voltage: 1.2V
7. Charging Current x Time: 3000mA x about 1.6h
8. Ambient Temp.
Charge Condition: 0 - 40°C Discharge Condition: 0 -50°C
Storage Condition
Less than 30 days: -20 - 50°C
Less than 90 days: -20 - 40°C
Less than 1 year: -20 - 30°C
9. Internal Impedance(after discharge to E.V.=1.0V) Approx.20mΩ
10. Weight: Approx. 62g
11. Size: 18.0(D) x 67.5(H) mm








This below thermal fuse is on each 10S Ni-MH pack. Any idea what break/connect temp spec ?

 

[amberwolf]

They don't use BMS on them because NiXX are self balancing, in that you charge them up to a general pack voltage of xS times the full cell voltage, at which point they drop to a lower actual voltage, then they dissipate the excess charge, if any, as heat. It's usually called Delta-T Delta-V charging.

There is usually a thermistor (rather than thermal fuse) in there for the special chargers used for NiXX chemistry packs so they can read the pack temperature and know when they have suddenly increased in temperature so they stop charging. Usually they also detect the drop in voltage, and stop for that, too.

If that is a thermal fuse rather than thermistor, then it may only be a safety cutoff and the charger for them probably only uses Delta-V.

There's a bunch of older threads about the charging / balancing, etc of this kind of chemistry, which includes details on why you can't parallel them safely (because of the way they charge, see above), at least not for charging. (once charged, if they are exactly the same voltage for each "stick" of series cells, you could then parallel them for discharge).


There are monitoring systems in large-EV systems with NiXX, to know when cells have failed, etc., but I don;'t know if they balance or not, beyond the self-balancing the cells can do. There are threads about those systems, too.

 

[Hillhater]

NiMh was used in early. RC CARS and Aircraft as well as cordless hand tools.
My 1999 Aprilia Ebike also had a 20s pack of 9ah “D+” size (32x90mm) cells, which weighed a ton compared to lithium.
Be aware, NiMh is very safe , but can bite if not treated correctly !
They “off gas” Hydrogen if charged too fast (common in the RC world !) .
…and i recall finding one 6s RC pack glowing red hot after a few minutes of reverse polarity charge !!

 

[amberwolf]

But it was only glowing red hot.

What would have (probably) happened to an equivalent lithium pack?


(I did actually explode some AA (or AAA, dont' recall which now) NiMH cells in a tricorder prop by charging them in reverse...destroyed the whole thing and left some shrapnel embedded in the room. )