I've recently got in touch with an old friend which uses a DeWalt DC735 drill for work, with a DE9116 charging base not meant for li-ion. One of his DE9502 2.6Ah NiMH battery packs is screwed-up.
Told him I can fix it with ease, but heck, there's not much info with regards to detailed reviews of sub-C NiMH cells. My only good reference right now is Hobby King and their Turnigy sub-C 5Ah and 4.2Ah cells. I wonder why are both cells equally priced. Found a complaint in the Rate and review section of the 5Ah cells. I wonder if cell binning and matching is the key here, because in such case the lower specced cells would be preferable (reliability is important).
I've sent Hobby King this question, but thought it could only do good to consult/share this here.
I rebuilt a few of those packs but I didn’t use NiMH cells. I probably could/should have.
What I do know is that you will want cells that either have the cardboard sleeve already or you will need to save the ones from the old batteries. The pads on the top and bottom of the pack are also good to save, if you can. One of mine ended up getting torn, so I used a piece of neoprene. It’s actually really good because it gives a little extra cushion and protects the solder joints if the drill is dropped.
Interesting aspect the 4200mah battery weights more then the 5000mah cell? 17 grams to be precise could the 4200mah be a better built cell? (Actually in the specs it says the 5000mah cell is slightly heavier). I am not sure what is going on there.
My hot glue gun should make short work of fixing the cells together. I'll see if those cardboard sleeves will go in or out. Cell size is probably going to differ, too. Hope they're not much bigger.
everydaysurvivalgear, a customer of the 4.2Ah cells reported 65g of cell weight. For the 5Ah cells, another german speaking customer reports 70.04g. This makes sense, of course. My guess is the actual weight figures are in the product description, but in general all I can say with regards to the overall product information is “What a mess!”.
The packs I took apart had sleeves over each individual cell. Many of the loose cells you buy won’t come with them. (Some do, like these:Cells with sleeves ) These were very important as the allow you to glue the cells together in formation before soldering. I would be VERY cautious when using hot glue around the plastic wrappers/labels that come on cells. It can EASILY melt the wrapper and you’ll short your cells. You don’t need the cardboard if you’re careful, but they’re a cheap reliable insurance policy!
No worries Sprinkles, I've used hot glue for battery pack assembly before without issues. Glue temperature is nowhere near close enough to be harmful for the cell wraps, cell cans never get in touch.
Now for the funny part. I've decided to go with the 4.2Ah cells, mostly because the charger is a 2A one and this way charging speed still is a tad above 0.5C or equal (4.2Ah cells' real capacity was reported 4Ah down to 0.9V by a customer).
Inquiry at Hobby King support centre:
Salvador Barqueros Provencio, Aug 27, 20:30 HKT:
Hello.
I am to rebuild a damaged DeWalt DE9502 drill battery pack. I see you have both 4.2 and 5Ah NiMH sub-C cells, my question is with regards to this. We look to maximize lifespan, thus I'd like to know if the 5Ah cells are binned with good enough consistency, or we'd better go with the 4.2Ah cells. Already told my fellow client to watch for the end of discharge battery voltage and to take a look at the amount of time the battery pack is held on the charger.
Of course, I have the expertise and necessary equipment for battery pack assemblage.
Richard Salarda, Aug 28, 13:39 HKT:
Hi Salvador,
Thank you for contacting HobbyKing. We appreciate you bringing this matter to our attention. With regard to your product related concern, I'll be forwarding this to our product specialist for further assistance. I assure you that we'll do our part to assist you with this one. Please patiently wait for the further response.
Have a great day ahead.
Kind regards,
Richard Salarda
HobbyKing Support Team
For self help on your HobbyKing inquiries, you may also check our Help Center by clicking "24 hour Support Centre" on the upper right part of our website
Salvador Barqueros Provencio, Aug 28, 15:20 HKT:
Thanks Richard.
We're going to presume his DE9116 (2A) charger dV/dt algorithm is fine. I didn't wanted to sound very alarmist to my fellow but I am aware that, since the new cells will be of higher capacity, the charger could have more trouble determining end of charge condition, a good reason for him to take a look at the charge time with the overhauled pack.
Hope these cells can really deliver 20+A with minimum voltage drop.
I'll wait for the specialist's advice. Thanks for your assistance.
Regards,
Salvador Barqueros Provencio
"Rescue" Rob, Aug 28, 19:59 HKT:
Hello Salvador,I would recommend staying with the 4.2V batteries. Both those and the 5Vs are solid and dependable but as you said I can't say if the charger will do well with the additional voltage.Let me know if you need further assistance.Regards,Rob
HobbyKing US Product Support Team
4.2V and 5V batteries? Can't say if the charger will do well with the additional voltage?
It’s near impossible to get good reviews of this kind of battery anymore, especially if you plan to use it in high draw application. To most people capacity is the ONLY thing they are concerned with. More is better, right?
Unfortunately as you push the capacity limit with this chemistry you also degrade the performance capabilities. Given the probabilities and knowing that 5A is pretty much the outside max for Sub-C size I’d suspect the 4.2A “may” be more reliable for a drill application. Trouble is, you have no idea where the cells really came from, how they are made, what their real capacity and performance specs are……and so on. It’s a bit of a crap shoot.
HK can and does post any specs they like. They do it for lipos all the time, BUT there is a large RC community that provides the same kind of feedback as BLF does and the real junk tends to go away. There is simply not much info on this size NiMh.
whatever you buy remember that you get what you pay for.
i wont buy anything but sanyo or panasonic sub c.cheap stuff wont last in this highly abusive service.
ignore the inflated whateverfire esque claims on the fancy cells.
i have never seen more than 3500mah.and it was a sanyo nimh sc.
the cardboard sleeve is for short protection.it will not melt at the high temps these cells experience during abuse.
like holding the trigger with the tool stalled.or 15 minute charging like my panasonic has.
reuse them or get cells with them.a nicd/nimh cell can infact explode with great force.
hot glue is a no no.
i have used ca and zip kicker to assemble packs that needed to be glued.
Low temp hot glue might be “ok” on cells with heavier pvc/vinyl wrapper, but the the thinner cellophane/plastic wrap on the cells you linked to can, and do, melt. (Speaking from experience.) I don’t doubt your knowledge or skills. I just don’t trust the cheap construction of the stock sleeve - that’s not what it’s made for.
(reliability is important).
