Author Topic: Replace the battery or the drill?  (Read 8077 times)

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dnix71

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Replace the battery or the drill?
« on: May 23, 2013, 10:52:58 PM »
For the 4th time in less than 10 years we are buying a new cordless drill kit at work becuase it's cheaper than replacing the batteries on the existing set. The dead set this time is a 18v DeWalt which retailed for $100 new with 2 NiCad batteries plus the drill and charger. The replacement is a Ryobi with 2 lithium cobalt/manganese batteries plus the drill and charger AND an impact wrench that uses the same battery. The Ryobi set new was also $100.

2 replacement 18v DC9098 DeWalt batteries are $100 (on Amazon). The least expensive new DC9098's were $56 for a pair on eBay, but the company will not buy on eBay because of Paypal and the liability of allowing someone using the company name to bid on eBay.

I managed to do  LiFePO4 conversion to one of the DeWalt batteries. Radio Shack's 270-407 8AA cell holder ($2.29) is the right length and width to fit inside the battery shell without cutting. I bridged out 2 cells with a wire, leaving six 3.2 lipos in series to give a 19.2v working pack. The amp-hours are only about 1/2 of the original 2/3's sub-C nicad pack but the current from the lipos runs the drill just fine.

The only hitch now is how to tweak the DeWalt charger. It charges the lipo pack and then errors out flashing red. The erroring out isn't a problem, but the pack voltage went above 26v before the charger gave up. A bad nicad pack doesn't do that. The bad packs we have only have 1 and 5 working cells left and the charger seems to know that and quits without overcharging either. The lipo pack didn't get hot and one overcharge didn't seem to ruin it.

The nice thing about having a spring loaded battery holder is if one cell goes bad it's easy to open the shell and replace that one to keep the pack fresh. In theory we should never need to buy another drill if I can get a charger that works properly.

The lipos AA cells are sold at Radio Shack, but they charge $10 for a 2-pack. From a US seller on eBay I get them for 1/2 that and just bought some to donate to the company to fix the drill.


Bruce S

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Re: Replace the battery or the drill?
« Reply #1 on: May 24, 2013, 11:03:14 AM »
Nice DIY!
I'd offer to send you Sub-Cs to use but those LiFePos seem to be doing the job  ;).
Can I ask you to PM me with the name of the dealer on eBay? Since you've had good luck with them I won't mind giving mine too.
I'm working on a programmable BME, for LiFePo units once done I'll certainly share it here, but with money getting even tighter I've had cut back on most of my hobbies  :(
Cheers;
Bruce S
Thanks!
Bruce S
A kind word often goes unsaid BUT never goes unheard

dnix71

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Re: Replace the battery or the drill?
« Reply #2 on: May 24, 2013, 12:37:48 PM »
The dealer this time is batteriesinaflash. They have a separate website under the same name.
The 4 packs are $10 and they are Tenergy, so you could go to Amazon too.
http://www.amazon.com/Card-Tenergy-LiFePO4-Rechargeable-Batteries/dp/B0057QCGRM
Actually cheaper than eBay if you buy at least 3 packs, then you get free shipping.

dnix71

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Re: Replace the battery or the drill?
« Reply #3 on: May 24, 2013, 11:01:29 PM »
The DeWalt battery charger would not work with the lipo pack I built. It would start off okay, but at around 21 volts it would suddenly kick up and raise the pack voltage above 28v. The open circuit voltage on the charger is over 55v. I'm guessing the nicads themselves are used to ballast the charger. I also discovered the original DeWalt charger will not work with my Wagan sine inverter. The charger flashes the code for supply power problem a few seconds after plugging it in. Switching it over to mains power stopped that.

eBay had a Tenergy charger for 6 cells for $11 shipped. That's cheaper than the original charger and the same make as the cells I'm using, so I bought the Tenergy charger. I may gut the DeWalt charger to use as a shell for the new charger.



« Last Edit: May 24, 2013, 11:52:07 PM by dnix71 »

GaryGary

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Re: Replace the battery or the drill?
« Reply #4 on: May 25, 2013, 09:01:09 PM »
Hi,
I'll just pass this on for what its worth.

I've had a lot of battery powered tools, and have the same experience as you did -- batteries go south and its cheaper to just replace the tool.  Seems very wasteful.

The exception has been the Panasonic 15.6 volt NiMh battery drill driver:
http://www.amazon.com/Panasonic-EY6432NQKW-15-6-Volt-2-Inch-Cordless/dp/B00009KDGY/ref=sr_1_4?ie=UTF8&qid=1369529716&sr=8-4&keywords=panasonic+nimh+drill
I think this link is to a slightly newer model than what I have.

The batteries on this tool have been amazing -- I think that mine is at least 4 years old and the batteries are still in good shape.  And, it has this reputation with trades people.
I do think that Panasonic is going to drop this drill from the line in a while, as its been out quite a while, and their newer tool use Li batteries.  But, I think it still remains a good deal for people who don't want to go through this planned short battery life that the tool makes like.

Gary

dnix71

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Re: Replace the battery or the drill?
« Reply #5 on: May 25, 2013, 10:43:42 PM »
GaryGary NiMH are better batteries than nicads, but I think drill makers were making speed chargers knowing it would shorten battery life. There is a thermal sensor mounted on one of the charger's contacts. Rather than slowly charge the nicads and not bake them, DeWalt went with something that boosts the battery up quick because people are using battery tools when they should be using corded. The only advantage nicads have over other chemistries is they can deliver very high current and get hot without immediately self-destructing.

I just got a dead pack from a church brother who does handyman work. He prefers DeWalt and Hilti over Ryobi and throws away a lot of dead battery packs. He said if you drop a tool while on a ladder that usually breaks it and the battery. I hadn't thought about that.

He also didn't notice that DeWalt embosses the year and country of manufacture right on top of the pack. The one he gave me was 2005 Japan. The ones from work were 2009 Japan. His pack used full size sub-C nicads instead of the 2/3 sub-C I got from work, but otherwise the pack is the same size. His pack even had balancing wires and a third tang. The work charger has the tang for packs with the balancing wires. The DeWalt kit we bought on sale had the smaller battery packs that lacked balancing wires, so that may explain why it was on sale. Balancing wires prevent overcharging.

We have the same balancing problem at work with walk behind forklift batteries. The sealed 6v only last a year or two, but Crowne says that's normal. I know for a fact they overcharge the 24v lift batteries to 30.6v because I put a meter on a lift and watched it. Someone is making money deliberately overcharging and ruining batteries.