How to bring voltage down

andsaw

Standard Member
I have a B & D wizard dremil type tool and have tried to restart the battery with no success, so i have a laptop transformer that is rated at 20v dc 5 amp and want to try converting it down towards the 3.6v for the tool, what would i need to do it if its possible and some simple sketch as im handy with soldering, i don't want to buy a new battery as it wont get used much and there expensive so just want a simple inexpensive solution to what i have already, so ideas please.
 

JayCee

Distinguished Member
I have a B & D wizard dremil type tool and have tried to restart the battery
You can't "restart" a battery, I presume you meant recharge it?
What is the current carrying capacity of the 3.6V battery? It should be stamped on it.
How is the battery charged...is it removable from the drill and inserted into a charger?
Is there a "rating" label or sticker on the body of the drill with it's power requirements printed on it?
 

andsaw

Standard Member
I tried charging it up with the charger, nothing, then tried the restart should of said revive, as seen on youtube
like this, there are plenty, but mostly the same, got a up to 3.2v and then tried recharging, nothing, the voltage just dropped away after testing with a meter, i don't know the rating as all it says is 3.6v its a B & D VP100 type 2 nicad battery and is removed and the charger is ok as i tested it, the tool is a VP940.
 

ChuckMountain

Well-known Member
NICADs die eventually after use and potential, particularly on high drain currents like Dremels and drills.

The above video can help get them back to a reasonable voltage if they aren't knackered so that a charger will recognise them and charge them. However I doubt whether they would be able to hold much charge, might be ok for a phone.
 

andsaw

Standard Member
I guessed the battery was dud, just need to find out if i can convert the laptop converter now.
 

ChuckMountain

Well-known Member
I guessed the battery was dud, just need to find out if i can convert the laptop converter now.
Ok I missed that point

So a replacement battery is: -

https://www.amazon.co.uk/AccuPower-battery-Decker-VersaPak-VP100-VP100CD/dp/B003WJJ5CU

£20 or as near as damn it.

Your laptop charge is 20V 5A which gives max power rating of 100W. Incidentally a mains Dremel are rated as higher as 130W so would not be suitable even if you could modify it somehow.

Its a non trivial problem, you would end up having to buy something like this

Full Function 15A Adjustable DC to DC Step Down Voltage Buck Converter Module for DIY Project -$10.87 Online Shopping| GearBest.com

which by the time you have paid the shipping will be as much as the replacement battery with no guarantee that it will actually work.

Nicad's can supply quite a high current due to their low internal resistance and to provide the same power levels as you decrease the voltage the current increases. As the current increases then so does the heat output hence the heatsinks on the above. The power supply might trip when it actually starts up.

I don't think its worth the effort. I would either buy a new battery or a replacement wired dremel.
 

12harry

Well-known Member
ChuckMountain gives good advice, except IF andsaw could get the laptop PSU conversion, it would outlast the replacement battery.
Worth checking if they make an AC adaptor to suit . . .but the whole point of such a tool is that it's handy and being battery-powered can be used without fear of electrocution. Those Laptop supplies are usually grounded to earth giving a route for any shocks.

andsaw might get a handy-electrics friend to make the down-converter into a proper box.... but it's still a risky setup and no G'tees. Have him fit two LEDs, 1= Input,. . . . 2 after a suitable glass fuse= Output. . . . May be worthwhile fitting two fuseholders.... one only contains a spare fuse.

If you don't know how to do these things, I guess you shouldn't attempt it. Reactivating rechargeable batteries is an art, which rarely pays off.
Good luck.
 

ChuckMountain

Well-known Member
ChuckMountain gives good advice, except IF andsaw could get the laptop PSU conversion, it would outlast the replacement battery.
Worth checking if they make an AC adaptor to suit . . .but the whole point of such a tool is that it's handy and being battery-powered can be used without fear of electrocution. Those Laptop supplies are usually grounded to earth giving a route for any shocks.

andsaw might get a handy-electrics friend to make the down-converter into a proper box.... but it's still a risky setup and no G'tees. Have him fit two LEDs, 1= Input,. . . . 2 after a suitable glass fuse= Output. . . . May be worthwhile fitting two fuseholders.... one only contains a spare fuse.

If you don't know how to do these things, I guess you shouldn't attempt it. Reactivating rechargeable batteries is an art, which rarely pays off.
Good luck.
It may outlast the replacement battery but there are too many unknowns. An unproven laptop PSU which may be quite old itself and might not last that long. PSU do unfortunately fail as well and particularly if its doing something its not designed to do and the load profile is completely different.

There is no guarantee that downconverter will work at the load either or has any safety certification.

Its going to cost for parts and mates time (beer or other poison) then to buy a new battery or even new mains power dremel. Plus its not going to go pop in your face.

These reactivations aren't that, they are just a fudge to get a reasonable voltage out of them. Unfortunately after doing years of doing RC cars once the chemistry of the battery has gone past a certain point you are not going to get it back. The voltage might be there but they won't take a load so as soon as you do apply it the motor will stall.
 
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