Instructables

HOW CAN I CONVERT LOWER VOLTAGE POWER TOOLS TO RUN ON HIGHER VOLTAGE BATTERIES?

I HAVE SEVERAL OF THE OLD SEARS VERSA-PAK POWER TOOLS THAT RUN ON EITHER 3.6 OR 7.2 VDC. THE BATTERIES ARE DEAD AND I DON'T WANT TO INVEST IN NEW ONES. I DO HAVE A 28VDC BATTERY AND CHARGER FROM A RYOBI POWER TOOL THAT IS NO LONGER NEEDED. CAN I SOMEHOW CONVERT THE 28VDC BATTERY TO EFFECTIVELY POWER THE VERSA-PAK TOOLS?

Andrew.F4 years ago
I don't really see anyway to do this so the charger/s are still useful to you, but...
you could open up the 28v battery and put the cells (assuming they are the same size and voltage) into the old dead battery cases.

Or

If the 28 volt battery can slide right into the 3.6 or 7.2 volt slot then...
you can open up the 28 volt battery and rewire the cells, so you will have the 3.6 or 7.2 volts but have more cells so you can run the tool longer. But I am not sure if you could use any of the original chargers on it.

long story short your best bet would be to transplant the battery cells into the old 3.6 or 7.2 volt battery cases but that's 'only if You can make the same voltage in the end
Andrew, the technology behind Ni-Cad and Mi-MH means all such battery's consist of cells operating at 1.2 volts.

Some more info

The reason they can be interchanged with non rechargeable cells of 1.5 volts is that their voltage in use drops at a steady rate down thru 1.2 volts and they die at around 1 volt.

The rechargeables have a different voltage drop curve, they begin at 1.2, and most of their life on a charge, they remain near 1.2,  only when discharged, suddenly the voltage drops to one volt, and the equipment stops working.

However, the rechargeable 9 volt battery, has not the normal 6 cells of a non rechargeable == 6 x 1.5 = 9 which if 1.2 only gives 7.2 instead its 7 cells of 1.2 equalling 8.4.
I got a neighbour, who used to repair power tools for Black and Decker back in the days power tools were repairable, and Black and Decker had repair shops in most cities in NZ, late '60s.

After Black and Decker closed its repair shops, he worked for a company servicing all brands of power tools, after he retired, he continued doing repairs at home, but kept up contacts with his previous two employers, as a source of spare parts.

According to him, some major brands, and certainly the shop/store brands use the same motor in different voltage drills. The drills with higher voltage batteries have a resister to make the lower voltage motors inside compatible with the battery voltage. Versa-Pak has no resister..

Black and Decker, I think were the originators of the Versa-Pak battery, I learnt about it from the UK, and it was sold in NZ. I suspect Sears' just stuck their label on Black and Decker supplied Versa-Pak systems.

There is NO 7.2 volt battery, only 3.6 volts, and the Versa-Pak tools are build, to fit one, two or four 3.6-volt batteries, according to what the tool does. It is one for a cordless screw driver, 2 for the various types of drills, 2 also for a sabre saw  the baynet saw and a detail sander. there was a held held vacuum cleaner, very much like other B&D models of the era, with built in battery, albeit the cleaner was white, not green as in Versa-Pak.  they also had various torches, and one was flexible like a snake. One was like a camping lanern, I suspect that had four batteries. (NO LED lights those days, the light bulbs were wasteful incandescent) Don't recall for sure what else used 4 batteries, I do recall a very small circular saw for breaking down sheets of plywood.

The drills would operate with just one battery plugged in, but half speed, I discovered that the variable speed drill, if used mostly on slow speed jobs, had a second life once the battery ran out. I just swapped the two batteries around.

Be aware a 7.2 volt supply is no good, as the electric speed control drill needs 3.6 volts at low speed

Mostly, the tools were underpowered. Once the batteries wore out, I did not replace them, but kept the tools to remove the motors to use for model making.

As for the chargers, they were "free" with the tools, the attraction for buyers was,  every tool purchased came with the batteries, which increased your stock, and all the batteries could be used in the same tool, so, out on the farm, you couild have one drill, a dozen charged batteries to start the day.

Really, even a new, fully charged battery, did not run a tool for long.

The chargers were either normal or fast, each held either a single battery, or a pair. There was a charger for 4 battery chargers, but I never had one, nor did I bother with a fast charger, as the both don't do a full charge, and they shorten the life of the batteries.

The supply was permanently wired to the battery holder, it was cheap after all. The supply was at 3.6 volts, the manual said, that charging two batteries would take twice as long as charging a single battery.

The supply as I said put out 3.6-volts, but unusually, it was AC. I am not sure why, it was for a modification, but I opened up the charger battery holder, and discovered a diode, which meant it was a half wave or pulsating DC charge.

As I said, it was cheap!!!! meant for department stores where the salesmen were totally clueless if a customer asked a question about the tools.

However, I am told the following, carefully opening the battery casing, which is a tube, you can refill it with 3 similar sized cells, from any cheap Chinese made cordless drill battery. I just took photos of what I have left, the batteries have been in a container for years, waiting for safe disposal (everybody takes safety, but nobody has supplied the means yet) One has begun leaking, so you can see how its labelling comes off, Sears' would have stuck on their own label.

As its 10-pm here in NZ, I am not going to slice one open, but basically its just 3 cells, with terminals soldered together. Elsewhere on Instructables you no doubt find instructions for SAFE soldering of Ni-Cad cells. WARNING, they can explode when soldering and they WILL explode if you take too long with the soldering iron. I think  to open the battery, careful go around the battery with a sharp knife about half way along, and after the battery has new cells, use tape to reseal then be careful in use, becuase the tape is not as strong as the original battery casing

But my intention was, if I needed these tools, was to open the tools and bring a cable out, and hook up that cable to a battery back which I would carry on a shoulder strap. In fact, I did bring out a cable on one drill, which using a short rod of steel, in the chuck, which i put into the chuck of a 240-volt drill to try the battery drill as a generator

Some of the tools use two battery's in series.for increased voltage, other tools, two in parallel, for long battery life. ==torch.

Using a 28 volt battery???? that is a big drop. In the old days, you could reduce the speed of a mains powered drill, i.e. 240-volts (In NZ) by putting a high wattage 240-volt light bulb in series with the drill. Not very efficient, becucse you lots lots of torque that way.

I have used a 14.4 volt charger to charge a 12 volt battery using two silicon diodes in series to drop the voltage. You need to be sure they are wired in the right direction, silicon drops I.2 volts (germanium drops a whole lot less, and they are used like the old crystal detector but modern pocket style radios)

And the diodes get pretty hot, so I do it outside, and ensure they are clear of anything that can catch fire. (I have a 6 volt door chime, for years its run off a 9-volt security system supply using 2 diodes to drop the voltage, very little current, so no heat, in any case, they are only powered a few seconds at a time, a few times a day.

But thats not viable for running a 7.2 volt drill from 28-volts. And in any case, 75% of the battery current would be lost in the form of heat, before it even ran the drill.

So go and buy the cheapest 7.2-volt cordless battery drill you can find, and use a short cable between that battery and your versa-pak drill.

But do they still make 7.2-volt drills? If they do, it will be cheap junk, and to make it even cheaper, the battery will be built in. AND you need 3.6 volts, So buy one, and toss out the Versa-Pak system.

Summing up, DON'T waste your time getting the Versa-Pak system going again, because you will just end with a toy workshop!!!!!!!

Why do you think Ryobi and every other brand is going with 28-volts tools?

And by the way, its not a 28-volt battery, its 28.8-v == 24 cells of 1.2-volts which equals 28.8-volts. With 28 volts, who cares if its NOT 28.8, but with 3.6 and 7.2, every fraction of a volt counts, anybody selling a cordless tool rated at 7-volts, would lose customers to brands rated at 7.2 volts.

For historians, I attach some photos, however, the charger units are in my workshop somewhere and I won't dig them out. Also the maunals are in my filing system (way back then, nobody had thought of digital files, so they are not on my computer network to quickly access. However, private message me if you want a PDF, but beware, they dont say much apart from warnings and how to plug in the batteries.

After all, they really weren't meant for much more than occasional use by yuppies that buy ready made workshops in department stores. I got mine, at give away prices when the store got out of power tools. The motors alone were well  worth it for the discounted price I paid and I got some chucks including a keyless chuck, and assorted bits and pieces.

The label on the drill says VP7521C 10-mm 7.2V (thats two batteries) 0-600/minute and made in PRC, the drill took full voltage at top speed it is a variable speed, but the second battery gets cut out, at the lower speeds. The two speed drill does the same.

Peter

Ps The photo of the batteries includes the cordless screw driver, with a battery inserted. I just thought too, that size cell (not battery) was also used in Black and Decker hand held vacuum cleaners

Sorry for the quality of the photos, I used my cell phone rather than proper camera.

m2.jpgs2.jpg2.jpg
jtobako4 years ago
Open up the power tool and check the voltage rating on the motor. There's a chance that you don't have to drop the voltage at all, that the limit on the power was because the batteries were cheaper that way. Oh, and hit the caps lock button-you don't have to yell to get attention here.
seandogue4 years ago
Technically yes. You *could rig it using a hefty regulator circuit from the 28V pack, but it would be messier than I want to get into. Yes it can be done...you'll need a big regulator to step-down the voltage and provide the current you'll need, and a modified shell from one of the old packs to route the power thru.