Black and Decker 12 v drill: Faulty battery charger

[Sylvain VAN DER WALDE]

Hello all.

I have this electric drill which is approx. a couple of years old (so I suppose we're dealing with Nicads). The charger unit consists of a a plug-in transformer with a 4-diode bridge (on a pcb) being located in the adapter. The markings on the transformer are: Output DC: 14.5 Volts, 220 Ma, 3.2 Va . The transformer is faulty (open circuit primary winding/connections). I've been unable to open the transformer housing (no screws, and a very tough casing). My question is: I would like to use an alternative transformer (cased preferrably), to replace the faulty one. I understand that in order to supply the 220 ma to the battery, the VA rating is important. Can you suggest a suitable AC transformer? I know that such a transformer without a load can give several more volts (12v = 15 v). Also, to keep to approx. 220 ma, might a 12 v transformer with a higher VA do, or what else might do? I don't normally have problems with the "usual" transformers, but this is somewhat different.

All info/advice will be highly welcome.

Thanks in advance.

P.S. I'm a regular reader of this group, and know that this question is not entirely off-topic.

Sylvain.

[phil]

Sylvian -

The "VA" rating is crudely the Volts X Amps - so at 240 volts - 3.2 VA at 14.5 volts comes out as 3.2/14.5 = 0.22 = 220 mA !

So you can buy a 14.5 V 3.2 VA transformer - or something of the same voltage and maybe slightly higher VA rating will be fine. Have a look at:

rswww.com

Either type in "transformer" in the search or try order-code search

201-8772

[John Weston]

I had a similar problem some time ago - the primary appeared to be open-circuit. What has (probably) gone is a thermal fuse in the transformer. I found this out after trying the fix (1) below

1. I ditched the transformer and cut off its lead to the charging base. I had a suitable NiCad charger, capable of charging greater than 12v batteries, and replaced the transformer with this. It worked better after I removed the diode in the battery holder (the only component in there), I believe this is only used to prevent the charged battery discharging through the transformer's secondary if the mains is turned off with the battery still connected. Using the NiCad charger instead of the simple transformer meant I didn't have this problem.
2. After finding this fix worked, and provided better charging times..., I cut the transformer case open with a Dremel (as one does to see what's inside :-) ) I found a tiny thermal fuse under the transformer was open circuit. Replacing these is not easy since they will blow if soldered. Hence it became irreparable...

NiCads are charged from a current source so be careful replacing the transformer with a wall-brick of apparently similar rating. The simple charger B&D use has sufficient output impedance to drop the charging current to a safe value even if the battery is flat (around zero volts) and be within the battery's charging current specifications for "normal" discharged voltages. A standard 14.5V 220ma voltage source may not have the requisite current profile for NiCad charging

[The3rd Earl Of Derby]

See how much a replacement is?

Benjamin Middlethwaite

[Sylvain VAN DER WALDE]

I had a similar problem some time ago - the primary appeared to be open-circuit. What has (probably) gone is a thermal fuse in the transformer. I found this out after trying the fix (1) below

1. I ditched the transformer and cut off its lead to the charging base. I had a suitable NiCad charger, capable ----------------------------------- of charging greater than 12v batteries, and replaced the transformer with this. It worked better after I removed the diode in the battery holder (the only component in there), I believe this is only used to prevent the charged battery discharging through the transformer's secondary if the mains is turned off with the battery still connected. Using the NiCad charger instead of the simple transformer meant I didn't have this problem.

Can you give me any details of that Nicad charger? Thanks in advance.

Sylvain.

[Sylvain VAN DER WALDE]

See how much a replacement is?

's £16.70 (incl. VAT and Delivery).

It's too much for what it is. I'd rather pay more for something better (using the existing charger adapter), or try to find a suitable transformer to replace the original one.

Sylvain.

-- Sir Benjamin Middlethwaite

[John Weston]

In true DIY style, it was a modified Vellman kit

from Maplin but I can't see it on their site today.

For other purposes, I had modified the circuit to give

12v and 14v output steps as well as the kit's 2.4,...,9.6v and replaced the jumpers with switches mounted in a case. I also modified the timer chip wiring to deliver the maximum current for a time to suit the higher AH capacity of modern batteries, and made this an external setting. I had also removed the discharger feature, since it is of questionable value for batteries as opposed to cells.

This was found to work fine with the B&D charger base.

It's not an "intelligent" controller, (e.g. delta-V) since these only work with individual cells. It simply sets a timer (1 or 14 hour, or modified as I did) for the approximate constant charging current's output.

Needless to say, a replacement "simple" 3hr charger from B&D is £15.99, but isn't as much fun, - or as highly specified :-) see:

[Sylvain VAN DER WALDE]

In true DIY style, it was a modified Vellman kit

from Maplin but I can't see it on their site today.

For other purposes, I had modified the circuit to give

12v and 14v output steps as well as the kit's 2.4,...,9.6v and replaced the jumpers with switches mounted in a case. I also modified the timer chip wiring to deliver the maximum current for a time to suit the higher AH capacity of modern batteries, and made this an external setting. I had also removed the discharger feature, since it is of questionable value for batteries as opposed to cells.

This was found to work fine with the B&D charger base.

It's not an "intelligent" controller, (e.g. delta-V) since these only work with individual cells. It simply sets a timer (1 or 14 hour, or modified as I did) for the approximate constant charging current's output.

Needless to say, a replacement "simple" 3hr charger from B&D is £15.99, but isn't as much fun, - or as highly -----------------------

specified :-)

Thanks for the answer. The Black & Decker charger is out of the question. It's pretty useless and unreliable. As for building something from scratch or modifying; my kit construction days are over. As a matter of interest (I hope), I bought my first kit (a simple valve audio amplifier) from Lasky's first shop in the Harrow Road, London. Old man Lasky himself was serving behind the counter. I also bought some radio kits (transistor) from Henry's. I first went to Henry's first shop, before it moved (the Marylebone flyover was being built). And again, old man Henry himself was in attendance. To save you asking, I'm 70 years "old".

Sylvain.

Sylvain. see:

[Dave Plowman (News)]

I've modified cheap drill chargers to constant current 14 hour charge types. There's usually plenty of room inside them to do this and the components required are cheap and simple.

[John Weston]

Agreed - the standard is not a good design. How about: (from the other thread - but I've not tried it)

has a 14v setting (OK for 12V) and 0.5 & 1A charge rate so should be OK (Might try one myself...)

Yup - I've done Lasky's and Henry's (etc) myself. Where's all the ex-army "junk" gone... :-)