# charging NiMH Batteries



## iaviksfan (Dec 27, 2007)

I just bought a Engine off ebay that has a 18v nimh battery in it. Since my other loco's are Lithium, i will need a charger, or not?
Would my Craftsman drill 18v charger work? The battery died and bought a new drill since it was cheaper than the battery pack, so i have this charger lying around.
Thanks
Greg R.


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## Del Tapparo (Jan 4, 2008)

You cannot use your lithium charger. You will need a charger designed for use on NiMh battery packs (18V). What kind of battery pack does your Craftsman drill have? I would buy a new charger.


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## K27_463 (Jan 2, 2008)

Nickel based chemistry charges in a completely different manner than Lithium. You can NEVER mix the two. You should get a new charger for the NIMH battery pack, they are not much. you should also color code you jacks and plugs to avoid any mistake in the future. Or, as an option, change out the 
NIMH pack to remain consistent on your line. Using a tool based charger that is designed for a specific size (MAH rating, not physical size) is also not recommended unless you can get exact specs from the manufacturer. 

Jonathan/EMW 
www.rctrains.com


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## iaviksfan (Dec 27, 2007)

i know you cant use a lithium charger. The question was if i could use the 18v charger from my old craftsman cordless drill, which was 18v nimh. Sorry if i worded that wrong. 
The charger has an output of 17.2v with something like 270ma. its either buy a new charger, make my old one work, or swap batteries to Lithium, which i didnt want to do at this time. 
Thanks, 
Greg R.


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## Tom Parkins (Jan 2, 2008)

I bought a cheap Harbor Freight 18v charger and use it for my NiMH 18v 3400 mah. Charges the battery fine. The charge LED light never turns green, but then it is a Harbor Freight Charger. I've used it for several years with no harmful effects.


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## Kovacjr (Jan 2, 2008)

Posted By iaviksfan on 12 Mar 2013 07:24 PM 
i know you cant use a lithium charger. The question was if i could use the 18v charger from my old craftsman cordless drill, which was 18v nimh. Sorry if i worded that wrong. 
The charger has an output of 17.2v with something like 270ma. its either buy a new charger, make my old one work, or swap batteries to Lithium, which i didnt want to do at this time. 
Thanks, 
Greg R. 

Not really recommended... You drill charger is 270 ma which is a real fast charge as these batteries/charger combos are designed for a fast charge for quick use. You train you can very well overheat and cook something inside the loco as it cant dissipate the heat. I recently picked up a Hitec X1 Charger and it is designed for all batteries. And its about a 70.00 street price. I brought it in to charge the receiver packs on my steam locomotives. 
http://www.hitecrcd.com/products/ch...arger.html


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## iaviksfan (Dec 27, 2007)

I never thought about the quick charge aspect of it. Thanks, This is why i post my questions here, to see the obvious things i over look.... 
Greg R.


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## K27_463 (Jan 2, 2008)

The first line of my post said"Nickel based chemistry charges in a different manner than Lithium" I said nothing about charge rate. While charge rate is important within each chemistry type in order to match to the battery pack in question, ( you can never charge small packs with too large of a C value) that is not the issue in a mismatch. 270mah is not a fast rate at all, and such a charger would take an extremely long time to charge a up a main motor sized pack- say 4000 or 5000 mah. 
Nickel based packs charge at constant current. The end of charge shutoff results from a detection of Delta V, of peak voltage. This is why you can now purchase Nicad/NIMH dual purpose chargers. They are designed to detect a large or small Delta V. NIMH delta is typically smaller than Nicad, , so early on Nicad chargers did not work well for NIMH, but the designers improved the peak detection for NIMH chargers eventually. The voltage used to charge nickel changes as the pack fills, ultimately reaching a peak and then falling off as internal pack resistance increases at the full point. This is why Nickel packs get hot under charge.. Lithium, on the other hand, charges at constant VOLTAGE. If you watch a smart charger with a digital display while charging Lithium, it will quickly find the optimum or correct voltage( Depending on some user settings) and stay there, while the current used for charging will rise and fall depending on the needs of the pack under charge. This is why any nickel charger cannot be used, they shut off on Delta v, and with Lithium, there is no Delta V. The are many other factors also, but this presents the facts as needed for this discussion. 
Jonathan/Electric modelworks 
www.rctrains.com 
24 years installing radio control battery in large scale, 40 years- give or take in electronics 
www.rctrains.com


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## Kovacjr (Jan 2, 2008)

Jonathan - he was not trying to use the Lithium charger as he stated in the post but a craftsman nimh charger to charge the nimh battery. At least that's what I took from his post when he explained it further on the 2nd one. I still don't like reworking special chargers for use on something it is not designed.


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## Michael Glavin (Jan 2, 2009)

Greg,

We’re assuming the existing NiMH in your loco are serviceable. I’d suggest evaluating the battery prior to any additional effort and or expense is pondered. NiMH batteries are not well known for a long service life. Check the voltage of the battery or better yet each cell individually if doable. An 18V battery should be comprised fifteen 1.2V cells. Monitor your batteries while charging/testing, look for excessive heat, generally heat is a tell for a bad cell(s).

All that said your 18V NiMH battery charger will suffice for now; it will allow you to charge and or cycle the battery pack to determine if in fact the battery is viable. Fast charging the batteries at 270mAh with sub-c NiMH cells is not a problem. Most of these cells are rated anywhere from 2300-4000mAh. On the lower end of the scale a depleted 2300mAh battery would require up to 8 hours to recharge. 2300/270=8.5 hours. These cells are well suited for fast charging in any event! Common sense would dictate you would not want to charge for any longer than say 60% of factored time required to fully charge your battery determined by battery/cell capacity and the charge rate utilized. 

If it were me I’d run the NiMH cells into the ground and roll over to Lithium when their exhausted.

Michael


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## iaviksfan (Dec 27, 2007)

Michael, 
yes that was my plan. Live with them until they die and/or find suitable Lithiums for it. 
Thanks everyone for your input. 
Greg R.


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## Greg Elmassian (Jan 3, 2008)

All good information. 

One observation: since nowhere that I can find the OP gives the mah of the pack, how can we assume any charging rate unless you have a smart charger, and even then many smart chargers do not vary the charging current.. (they are not that smart ha ha!) 

I won't charge anything until I know the mah of the battery. 

Also, nicads end of charge is signaled by a negative dv/dt (dv means delta (change) voltage over dt (delta time).... i.e. at full charge the charging voltage will actually go down a bit over time 
nimih end of charge is zero dv/dt ... so it's a bit different... 

for years I monitored charging voltage with a precision meter to double check proper end of charge recognition. 

Greg 

Greg


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