Repairing/rebuilding drill battery packs

[soldar]

I have two nicad battery drill/screwdrivers that failed in the same way. The nicad battery packs failed. The charger was just a transformer followed by a rectifier bridge. One element of the battery pack failed shorted so the battery pack would be at lower voltage which made the charger overheat which blew a a thermal fuse integrated in the transformer and that was the end of any charging.

I have not repaired the nicad battery packs nor the chargers. They are on the to do list.

For now what I have done is (1) connected cables to the drill so I can feed it 18 V from an external power supply (all are 18 V). Not so convenient but it works.  And (2) the lithium ion battery packs from my Ryobi drill can fit and power both the other ones, not perfectly but it works.

I still have some nicad battery packs which are ok but they are a pain to work with bceuse they sef discharge and they are always dead when I need them. I suppose I could devise some trickle charger to keep them topped off but it may not even be worth the effort as I am mostly just using the Ryobi lithium batteries.

Ideally I would like to rebuild the nicad packs with lithium cells. That way they would fit correctly into the drill instead of the shoddy way I am doing it now.

So the question is how can I rebuild the 18V battery packs with lithium cells. I know lithium cells require control circuitry integrated in the pack so it is not just a matter of filling the space with lithium cells.

So thee are consideration with form factor, control circuitry, charger circuitry, etc.

Is this easily doable and how?

[JJ_023]

I think it's totally doable.  You would need 5 18650s.  They have already make PCB circuits that handle the charging the discharging and Balancing of the pack.  You would also typically use a poly switch for reverse polarity protection if that was an issue.

There are also plenty of companies that will sell you a complete battery solution for 18 V.

[soldar]

I think it's totally doable.  You would need 5 18650s.  They have already make PCB circuits that handle the charging the discharging and Balancing of the pack.  You would also typically use a poly switch for reverse polarity protection if that was an issue.

There are also plenty of companies that will sell you a complete battery solution for 18 V.

Thanks. I have been reading quite a bit.

On the physical/mechanical side I suppose I just need to make sure the cells will fit into the pack enclosure. I suppose I can do a mock-up with dowels and test.  Assuming this works out I need to figure out the electronic part.

It seems I need to provide a "Battery Management System" (BTS) and I see them on sale on eBay and Amazon.

I do not see Lithium batteries for sale online. Amazon search just sucks. Probably a part of it is that they will not ship lithium batteries due to danger of fire. Also, I am hesitant to buy them without being sure of the quality as it seems there is much junk and fakes for sale. I don't know where I could get good quality batteries.

After spending some hours investigating it seems to me that, although I could do it, it would be somewhat complicated and expensive. Probably not worth the expense and the effort since I can used my tools with the battery packs I rigged from Ryobi and it's not like I use the tools every day.

I think I have learned enough so that I could attempt the repair if I get to the point where I really need it.

Thanks.

[uli12us]

I don't know, what brands are buyable in Spain. Unfortunately Ryobi batteries are the badest suitable part for the other drills. If you have a battery without the shaft inside the
handle of the tool, it is much better. Lidl should be the biggest dealer for groceries in europe after that is Aldi. Both have their own line of Batterie driven tools.
If you remove the Box with the batteries from the tool, use only the upper part that fits to the drill and make or buy an adapter for Aldi, Lidl or other flat battery packs and connect it together, you can use standard batterypacks for your drills. The BMS is in the batterypacks so you don't have a problem with it.

[soldar]

I don't know, what brands are buyable in Spain. Unfortunately Ryobi batteries are the badest suitable part for the other drills. If you have a battery without the shaft inside the
handle of the tool, it is much better. Lidl should be the biggest dealer for groceries in europe after that is Aldi. Both have their own line of Batterie driven tools.
If you remove the Box with the batteries from the tool, use only the upper part that fits to the drill and make or buy an adapter for Aldi, Lidl or other flat battery packs and connect it together, you can use standard batterypacks for your drills. The BMS is in the batterypacks so you don't have a problem with it.

As I said and as can be seen in the photo, the Ryobi packs work with the two other drills even if they do not fit and lock exactly in place. They work just fine.

I was considering repacking the original battery packs which have 15 nicad cells of SC (sub C) size. I could rebuild them with 15 NiMH cells of the same size or with 5 lithium cells. Lithium would be more complicated due to the physical space and the need for a BTS.

NiMH would be simpler as it would be the same size and number of cells.  But looking around I see the cells are too expensive and just not worth it. It would be at least 50 EUR just for the cells plus the trouble of assembling the pack and this is for something I really do not need that much, just that it would be nice to have the original pack rather than use the Ryobi.

If I could get 15 NiMH, SC, cells of at least 2400 mAh for 25 or 30 EUR max then i would do it.

For now I can use the Ryobi packs and also direct 18V from external PSU.

[BILLPOD]

Run the drill make and model and 'battery' through Google and see what comes up.   I found 'rebuilt' batteries for my 12 volt Dewalt drill at a decent price, and I have been happy with them.

[elektryk]

I did some battery pack mods with 18650 and 21700 cells.
It turns out that INR21700-40T are quite powerfull, on this pictures you can see 4s 4Ah pack.

I've used T12 iron to solder them before getting that spot welder, with a spot welder it is a 10 min job.

[calzap]

If you look online (try Amazon and eBay for starters), you can find adapters that allow Li battery packs to be used on tools originally designed for NiCd/NiMH.  With the adapters, I use Makita 18V Li packs on 18V Makita and Dewalt drills and saws that originally used NiMH packs.  I know adapters are made for Milwaukee and Ryobi too.  The Makita Li charger is nice too … quick with informative status lights.  And it’s great to use only one type of battery and charger instead of two or more.

Mike

[elektryk]

But be carefull with adapters, there's always risk that you will discharge cells too much.

[calzap]

Good point.  My understanding is that for Makita, over-discharge protection is in Li-rated tools, not the battery.  Not sure about the latest Makita batteries.  We're careful to switch batteries as soon as the tool seems to decrease power.   I could probably put a MOSFET in the adapter to shut off  power if the the battery voltage drops too low.

Mike

[calzap]

I researched whether Makita Li batteries have built-in over-discharge protection.  Makita was of no help in this.  18 V, 5 and 6 AH batteries produced since 2019 (maybe since 2017) have it. There’s a good video by Tool Scientist on the topic.  See the link.  If the current draw is above 5 A, the battery will shut off at about 12 V.  Strangely, if current draw is under 5 A, shut off doesn’t occur until voltage drops to about 8.5 V, which is on the low side.  Apparently, most tools draw 5 A or more.  My rule has been that as soon as a tool starts to slow down, swap batteries, which has worked well.
Mike

[elektryk]

I didn't play with Makita packs but:
-Milwaukee M18 has SO8 P-FET at charge pin, B+/B- leads are connected directly to the tool, so there must be some kind of communication beetween tool and pack,
-Metabo LiHD 18 has a high current fuse and no power mosfets at all, there are B+/B-, NTC and comm pins,
-Bosch 18V has a series diode for charging pin and a resistor for ID pin.

Both Milwaukee and Metabo have some microcontrollers inside, Bosch doesn't (so it is the easiest one to repair IMHO).

In all of above cases there's a possibility to overdischarge them with NiCD/NiMH tool.

I'm not sure how does it look inside the Ryobi pack from OP, but I think it's worth to check before using it with adapter.

BTW Nice FET on that PCB from Makita. The only problem with that packs is that charging controller can be locked...

[spostma]

You can buy Ryobi NiCD -> lithium replacement packs + charger off-the-shelf from AliE:
https://www.aliexpress.com/item/1005005496587468.html

and all kinds of adapters:
https://www.aliexpress.com/item/1005002959333472.html
https://www.aliexpress.com/item/1005005196305243.html

[soldar]

I think some of you are missing the point of what I am trying to do.

I have two no-name drills which use their own proprietary types of power packs and those power packs are dead and I am looking at rebuilding them with new cells.

I am not looking for any kind of adapters because i do not need an adapter as the Ryobi packs will fit (not perfectly) and work just fine.

I am looking at rebuilding the original ni-cad battery packs with Ni-MH or with Li-ion cells

[elektryk]

I am looking at rebuilding the original ni-cad battery packs with Ni-MH or with Li-ion cells

In this case BCM from my photo should do the job, there are version for 3s, 4s and 5s (changeable with SMD jumpers).
First check if 5 18650/21700 cells will fit into your old enclosure.

[soldar]

In this case BCM from my photo should do the job, there are version for 3s, 4s and 5s (changeable with SMD jumpers).
First check if 5 18650/21700 cells will fit into your old enclosure.

Yes, in the case of Lithium I would first have to do a mock-up with wood "batteries" to see if or how they fit.

The advantage of 1.2 volt SC Ni-MH is that they would take exactly the same space as the old nicads (and do not need BMS).

In any case I would need to shop around for batteries because in Spain they are way too expensive. I would probably have them brought over from America. I would not want to spend more than 25 or 30 euros because, as I say, I am using the drills with the Ryobi batteries and can use them with external 18V PSU.

[armandine2]

I researched whether Makita Li batteries have built-in over-discharge protection.  Makita was of no help in this.  18 V, 5 and 6 AH batteries produced since 2019 (maybe since 2017) have it. There’s a good video by Tool Scientist on the topic.  See the link.  If the current draw is above 5 A, the battery will shut off at about 12 V.  Strangely, if current draw is under 5 A, shut off doesn’t occur until voltage drops to about 8.5 V, which is on the low side.  Apparently, most tools draw 5 A or more.  My rule has been that as soon as a tool starts to slow down, swap batteries, which has worked well.
Mike

I didn't really follow that explanation - especially the bit about the scope leads.

I've stopped buying Makita batteries - in the interest of science 

[calzap]

Yeah, I had to watch it a couple of times.  He moves fast.  I think the shorting occurred because he has a portable scope and assumed the channels were electrically isolated including the grounds.  So, he put the ground leads on two objects that had a potential difference, and zap!   Folks have suffered far worse consequences making that wrong assumption.

Mike

[JJ_023]

In this case BCM from my photo should do the job, there are version for 3s, 4s and 5s (changeable with SMD jumpers).
First check if 5 18650/21700 cells will fit into your old enclosure.

Yes, in the case of Lithium I would first have to do a mock-up with wood "batteries" to see if or how they fit.

The advantage of 1.2 volt SC Ni-MH is that they would take exactly the same space as the old nicads (and do not need BMS).

In any case I would need to shop around for batteries because in Spain they are way too expensive. I would probably have them brought over from America. I would not want to spend more than 25 or 30 euros because, as I say, I am using the drills with the Ryobi batteries and can use them with external 18V PSU.

Keep in mind that if you can't get 18650 to fit into the case you can always go to a smaller battery size.  There are a few sizes in between 18650 and cr123 rechargeable.  Which means you can definitely make this fit, the only thing is you would just sacrifice capacity.