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Doc Nickel
02-01-2008, 04:59 AM
As I was using some cordless tools a few minutes ago, and had to run out to the shop to get the battery charger, my brain came up with that as a joke, but after a bit of thought, that's not only possible, but easy and workable.

The cordless battery charger. As in, a battery-powered battery charger.

Just take something like one of these (http://www.xantrex.com/web/id/63/p/1/pt/10/product.asp), and instead of the 12v-110v inverter, just add a 12v-18v booster and the charging circuit, then mold in half a dozen DeWalt (or whatever brand) sockets to the top of the case.

That big ol' lead-acid ought to feed a handful of on-gun batteries maybe a dozen or two times, and that's plenty for the average jobsite for a day or two. Quieter than a generator, no exhaust...

No, it's not the end-all, be-all, but mark my words, within eighteen months, you'll see somebody- probably a big name cordless maker- offering something like those "jumpstart packs" with charging sockets built in.

E-mail me for the address to send the royalties to. :D

Doc.

ptjw7uk
02-01-2008, 07:46 AM
Only problem as I see it the danger of overcharging and them blowing up if you forget they are charging.
Most fast charge batteries have an over temperature device in them to stop the charge when the battery gets a bit hot.
I remember when fast charging model boat cells in 15 minutes you just put em in a plastic bag and dunked them in the pond, the plastic coverings did not last long with the quick charges.
I see Bosch now do a 15 minute charger although at a price!
To do the job properly you may need some extra electronics in the system or at the worst a timer. I have some black and decker drills that have 6 hour charging batteries so I built a six hour charger for them so if I forget to turn them off at least they do not get all night charges.
I have nearly had 2 fires from drill batteries in that they were smoking after the so called 1hour chargers both failed to switch off. I took the drills back and spent extra to get a decent make of drill. Both were from our B&Q 36volt drills but a bit cheap - so now I only get branded drills a fire is to easy to start with all the power stored in the batteries.

Peter

dp
02-01-2008, 04:10 PM
If you open up a charger for an 18v battery you'll find the first thing that happens is the 115ac is reduced to some lower DC voltage (which is further regulated and attached to thermal sensing circuits). Match that with batteries and you have what you need. It provides portable power to a regulated charger stand. But how do you charge the batteries that power the charger stands? Portable generator would do it. But, you ask, why bother with the batteries in between then?

macona
02-01-2008, 04:22 PM
With a lot of newer cordless tools being lithium based you need specific chargers to charge them safely. Easiest thing to do would be to get a deep cycle battery and a cheap inverter and then plug in your chargers.

Most new chargers no longer use mains transformers internally. They are mostly switch mode type power supplies.

Doc Nickel
02-01-2008, 04:44 PM
Sorry guys, bit of a mix-up.

I don't need a cordless battery charger, and I wasn't saying I want to build one. I barely have a need for cordless tools, let alone a cordless charger.

I was just throwing that out there partly as suggestion/idea for others, and partly because I know somebody's probably working on one, and you'll see a commercial version on the shelves before too long.

As I said, I originally thought of it as a joke- you know, cordless battery charger, dehydrated water, solar-powered flashlight, DVD rewinder, etc.

But once I thought about it for a bit, as I said, it'd be easy and simple and just takes off the shelf parts. Whoever builds one just needs to make a controller circuit that takes the juice from the big battery pack and conditions it to run the charger- whatever that takes.

Lithium-ion feedback controls, rapid-charge monitors, whatever's built into the tool's battery charger now, it'd be trivial for the engineers to swap from a 120VAC input to a 12VDC input, and after that, it's simply a matter of injection-molding the new big-battery case with a few charger sockets molded in, and slipping in a couple of LEDs or a digital readout for big-battery charge and condition.

Me, personally? I still use wall-power tools.

Doc.

macona
02-01-2008, 04:54 PM
Ahh, i see now.. ;)

Actually it would be non-trivial to redesign as most Li-ion packs are around 18v + so you would have to design in a DC-DC converter. It would, in fact be a complete new design from the ground up.

I do have ni-mh chargers for things like my AA/AAA batteries that run off 12v though so the idea is not that preposterous. And I am sure I have seen older cordless tools with 12v chargers to charge in the field.

darryl
02-01-2008, 06:14 PM
I've wanted to put a higher capacity battery in my toolbox that I take on the job- (notice that I didn't say lead ass-heavy-cid)- so I can rely on the charge to make it thru the day. I'd use some of the drills that are useless now because their batteries and or chargers have died. I'd wire the drill to the toolbox. Almost all the time the toolbox goes with me into each room and seldom do I need to be far from it with the drill. I'd just have a plug-in wire from the toolbox. The drill itself would obviously be lighter, being without its own battery pack, and smaller to boot, which gets it into tighter places. The price I'd pay for this convenience is carrying the extra weight of the battery and of course the drill would no longer be cordless. I'd still have a cordless as well with me. I would have one of those switching power supplies in the box as well, so if there's power in the building, I could keep the battery up. If there's no power, which is often the case, I can still work as long as I've charged the battery to begin with. Comes to mind I could rig up a wire in the trailer to charge the toolbox battery from the vehicle whenever we're enroute.

Because one high-tech charge method is to supply pulses of high current to the battery, it would be a good application of electronic technology to design the inverter (required to charge a higher voltage battery from a lower voltage one, as stated) to deliver an inverted pulse train. That's a pretty easy circuit, and the only thing to add is a control that monitors the battery and stops the inverter when the charge is complete. The inverter transformer could have various taps on the output winding to be suitable for several battery voltages. Something like this would be less lossy than say a resistive voltage dropper that might be required in the case of a lower voltage battery being charged from the mondo 12v one.

It would definitely be a custom circuit and you'd probably have to replicate whatever means the manufacturer uses to monitor and safely charge the particular type of battery. We use three different batteries on the job, 12v nicads, 14 v nicads, and 18v nmh's. If I get my act together, we'll also be using a lithium pack or two. I'd have to be able to charge all of them from my toolbox if I wanted complete versatility from this system. Hmm. I'll have to think on this.

2ManyHobbies
02-01-2008, 06:31 PM
Think about a roll-away toolbox, the handtruck kind and not the upright ones. Use modified guts out of one of those emergency kits (flashlight, radio, compressor, phone charger, jumpstart, 400-600W inverter) to include common power tool battery charging points for the top shelf/tray. Done right, you could have a built-in extension cord for charging. I was going to say keep the compressor for something like a brad nailer, but it would be more efficient to have it charge battery packs for electric nailers.

For accessories, you have a trickle charger in the truck box so that it can power up on the drive home.

I could see HVAC, plumbing, and electrical contractors going nuts for that sort of thing.

jdunmyer
02-01-2008, 08:51 PM
I've heard horror stories about cordless tool chargers/batteries causing fires when left "on charge" for too long. Besides, I've noticed that most times, the batteries will feel a bit warm, even after they're fully charged. Although many folks just drop the battery in the charger and forget it, even for weeks at a time, this doesn't seem like a good idea to me. Soooo..

I bought a 12-hour timer, the kind that is often used for a whole-house fan. They're actually a wind-up clock movement, but seem to work well. Installed one in a box, next to a dedicated outlet for the chargers. Set the batteries in the chargers, twist the knob for a few hours' charging time, and forget it.

Did the same thing on the outlet for my vibratory cartridge case cleaner so I don't forget it, and can turn it on when I leave the shop and not have to listen to it working.

darryl
02-01-2008, 10:22 PM
Some of the chargers will drain the battery pack if they're unplugged and a battery is left in. We had a problem with a brand-name charger a few years ago, and this is what it boiled down to. Something to be aware of.

Pretty much all rechargeable packs get warm while charging, and when full charge has been achieved, the charging current turns into heat. This is what allows temperature sensing to be used to terminate a charge. Some chargers use this idea. I built one many years ago based on this principle, and it brought back some life to the packs in use at that time.

If a charge continues after the cells have topped, they will heat up and can become damaged or worse. If one cell shorts, the charger can become confused and will continue to put out a charge because it's not sensing the voltage has risen to the full charge level. Chargers that don't also include temperature sensing can be dangerous to use. I've never had a pack explode or otherwise vent the magic smoke, but I believe that it can happen.

One drywaller I know dropped a pack from the ladder, and it happened to land on a drywall screw that also just happened to be standing upright on the floor. The pack impaled itself on the screw, which shorted out the pack and it self-destructed. It didn't explode, but it must have vented, and was melted in spots. It was a mess.

On my electric toolbox idea, the battery would also be used for a built-in light, partly for finding stuff in the toolbox, and partly for light during clean-up and trailer loading. That 'limitation' has bitten again this winter season. Pretty hard to gather all your tools up when you can't see a bloody thing.

I see two main negatives- one is weight, so a high power to weight ratio pack would be good, and the other is charge retention during non-use. Probably a well protected lithium pack would be the answer.

wierdscience
02-01-2008, 11:23 PM
Something similar to this maybe?

http://www.freeplayenergy.com/products/portable-power/weza


And then there is this for when you go sowhere and forget to charge your cellphone.

http://www.freeplayenergy.com/products/portable-power/freecharge12v

J Tiers
02-02-2008, 12:09 AM
Do NOT try to use the usual type battery charger with an inverter, UNLESS you have a true sinewave inverter.

Many chargers actually use a specially made capacitor as the series element to reduce the line voltage to battery voltage, and then a complex control circuit to regulate voltage and charge rate.

The capacitor is ONLY able to do it's job if the input is 60 Hz (or maybe 50 hz). The "edges" on the usual "modified square-wave" inverters will cause the inverter to draw too much current and pop the internal fuse.

I know, I have fixed them for friends.

DeWalt at least USED to have a 12V input charger for their tool batteries. It is (was?) pretty much exactly what you refer to, although intended for use in a vehicle.

Paul Alciatore
02-02-2008, 02:05 AM
Oh, forget that. What the world needs is a solar powered night light. Solar cells, rechargable batteries, photocell and electronics to turn it on at night and off in the day. It should only cost about $150 or so and another $100 or $200 to install in your hall. The tree huggers will love it. You could sell a million easy.

gearedloco
02-02-2008, 03:53 AM
Oh, forget that. What the world needs is a solar powered night light. Solar cells, rechargable batteries, photocell and electronics to turn it on at night and off in the day. It should only cost about $150 or so and another $100 or $200 to install in your hall. The tree huggers will love it. You could sell a million easy.

And, if you arrange it so that the light from the lamp shines on the solar cell, you could put the whole thing inside - no need to run wires outside to the solar cell. And if you used LEDs for the lamp you'd never have to worry about the lamp burning out. And since they're more efficient, you could use a smaller battery and solar cell.

Ain't science wonderful!

wierdscience
02-02-2008, 09:43 AM
And, if you arrange it so that the light from the lamp shines on the solar cell, you could put the whole thing inside - no need to run wires outside to the solar cell. And if you used LEDs for the lamp you'd never have to worry about the lamp burning out. And since they're more efficient, you could use a smaller battery and solar cell.

Ain't science wonderful!

And it needs to made overly complex and from some rare toxic element so everytime the bulb burns out you must replace the entire unit with the old one hitting the landfill never to be seen again.

BTW: Be sure and vote for Change this November!;)

This ad paid for by citizens to elect Change.

jdunmyer
02-02-2008, 11:11 AM
Darryl said:
Some of the chargers will drain the battery pack if they're unplugged and a battery is left in. We had a problem with a brand-name charger a few years ago, and this is what it boiled down to. Something to be aware of.

Interesting observation, I'll keep that in mind!

The idea of a larger battery to charge cordless tools on a job site is actually pretty good. I can see uses for it for some construction work.

J Tiers
02-03-2008, 12:57 AM
The idea of a larger battery to charge cordless tools on a job site is actually pretty good. I can see uses for it for some construction work.

No doubt why DeWalt made them.............