Yet another noobie power supply???

[torker]

Hi you all! I've been hanging out here when I can....Wow...there is a ton of info here! I'm a total electrical dummy! As time permits I'm trying to learn more about it but right now I'm stuck. I built a quill drive unit for my mill/drill. It uses a 12 volt wiper motor from a late 70's Chevy. I've tried other's advice from other boards but am not having the success I want. I tried several computer supplies but they don't have any jam. Now I'm using a 1000cca 12 volt battery and a 12v charger running at 2A. When the thing first starts out it is almost acceptible but the battery doesn't take long to discharge to the point where it will no longer operate. I'm running the motor through a 7 to 1 reduction. I do know I need more reduction and am in the process of making gears for 150 to 1 reduction. I need to really slow this down for drilling with bigger bits and for boring large holes. I have to get the power supply issue settled first though. Right now it is running through a PWM controller (good to 30V). I have no idea how much power a 12V wiper motor actually makes or how much power a proper supply should have for this setup. I'm sooo close....it's very cool watching this thing drill and bore holes all by itself. The problem is I need the controller WIDE open to do anything and it's pretty tricky to stop it when it breaks through while drilling (yes I need a limit switch). I realize this is "hillbilly" tech to most of you guys and I do want to get into CNC at some point but there are just not enough hours in a day to learn all this in a short time. Thanks!
Russ

[H500]

From what I remember, old wiper motors take a good 10 amps steady and possibly 10 time that much when starting up. I suspect that you will need to run it off a 20-30 amp battery charger. The cheapest way is to rewind a transformer from a dead microwave.

Are you sure your pwm controller can handle such large currents?

Why don't you use a variable speed electric drill instead of a wiper motor?

[torker]

H500..Thanks for "guesstimate" on the power required! I think you are about right. The actual wipers use a 15 amp fuse so that would be in the ball park. Here is what I've got so far


BTW...I've had drills and electric screwdrivers etc all suggested before. I even tried a drill. It was a witch to mount...the plastic case wasn't made to clamp down like this wiper motor can be. Also...the drill (a 3/8" Makita VS) heated up really fast. The wiper motor, even lugged right down, does not heat up. The DC wiper motor is also a lot smoother...it makes a lot nicer finish when boring holes. With this setup I have bored 2" holes in 1" thick mild steel, hands off with no problems...other than the battery losing power. Also..I tried using the 10A side of the charger to run this on but the charger heated up considerably. This setup does work...it's run steady for 1/2 hour under load with no problems...except it's too slow. I don't want to put together a backyard power supply...#1..I don't know enough about it and I like this thing enough to spend some money on a good power supply. The PWM controller I bought ;
Supply voltage DC 6 to 36 volts
Load current 16 amps permanently
Will control loads of up to 1/2 hp
I just need some suggestions for a proper power supply. Thanks again!
Russ

[H500]

That looks like quite a setup. Did you look at using a gearmotor?

If your 10 amp charge is overheating, that means that you are probably drawing a lot more than 10 amps. Did you run it with the charger and battery attached, or just the charger?

A ready made 20amp linear power won't come cheap. You're probably looking at several hundred dollars unless you can find a surplus unit.

It's not that hard to do your own supply. All you need is a transformer, bridge rectifier, filter capacitor and fuse. There's lots of instructions posted here.

A 30 amp computer supply might work if you add a large filter capacitor at the output.

[torker]

H500..Yes I did look at a gear motor setup. Ha...I should mention, I'm up in the boonies in BC, Canada and there is nothing like this in our town. Nearest stuff is 4 to 5 hours away...one way. Agreed, a gear motor would be so simple but the few that I found where too big or the motor had to sit the wrong way etc. Wiper motors are cheap and are actually fairly good motors so I'm finding. They must be pretty decent, I've driven steady for 10 hours in heavy,wet snow, with the wipers on the whole time (moving a lot of slop) and they just keep going. Yes, I do have the battery and the charger hooked up. This was only temporary anyway just to see if this would work. The battery is a bit old and the charger is a cheap one. It gets hot just charging a battery. Besides, having a battery in the chip pan and a charger on a bucket isn't very tidy...lol! Also...I'm going up to around 150 to 1 reduction as soon as I get the new gears finished, this will make a big difference in the power and draw I'd think. I was thinking of this power supply
http://www.mpja.com/category/Single_...Y_15078_PS.asp
Anyone have any thoughts on this supply? Thanks!
Russ

[H500]

Russ, that's a switching power supply...essentially same as a computer power supply that you could pick up for free. If you already tried a computer supply and it didn't work, then this one likely won't work neither. What you need is a LINEAR supply...it's a big heavy SOB. A 20 amp will probably weigh about 15 -20lbs and cost a lot more.

[Al_The_Man]

Originally Posted by H500 .essentially same as a computer power supply that you could pick up for free. If you already tried a computer supply and it didn't work, then this one likely won't work neither. What you need is a LINEAR supply...it's a big heavy SOB. A 20 amp will probably weigh about 15 -20lbs and cost a lot more.

A PC power supply current rating for the 12vdc is very low, they are made for high current on the 5vdc mainly and PC supplies are notoriously over-rated, wattage wise.
Also you do not really need a regulated supply for this application, a standard linear un-regulated would work, the final output can be anywhere from 12 to 18vdc as these motors do not require precise voltage to operate.
Al

[torker]

Thanks guys! H500...the computer supplies that I tried where from old 486's and didn't put out enough 12V. A fellow sent me a big whopper of a computer supply. It has a 24V outlet on it but it's out of one of the small wires instead of the big, heavy wires that the 6V comes from. I thought the 24V would work fine but as soon as I turned the power up to over half the motor would nearly die. It was drawing too much juice I guess. Another thing I should have mentioned...I use a 15amp in line fuse on this and haven't blown it yet. So I need a linear supply...hmmmm back to google. I'll send a couple of emails out to some suppliers. Thanks again!
Russ

[H500]

Originally Posted by Al_The_Man A PC power supply current rating for the 12vdc is very low, they are made for high current on the 5vdc mainly and PC supplies are notoriously over-rated, wattage wise. Al

That's true for AT supplies, but the 12v on an ATX ps is typically rated for 15-25 amps. But that's actually a good point. If the supply he tested was an AT, then it would explain why it did not work.

[H500]

Russ, you might want to try one of the newer ATX computer supplies that has a high rating on the 12v. They can put out much more current than the 486 ones. If it works, it might save you some $$
Here's an example:
http://www.tigerdirect.ca/applicatio...&sku=P456-4002

[torker]

H500...thanks! That looks like it'd have some ooomph that I'm looking for! I think I'll call our computer guy and see if he has something like that. I asked him awhile ago but he didn't have anything at the time and was too busy to take it any further. thanks again!
Russ
BTW..I just noticed, that is a Canadian company...bonus! I think I just might order that in the next couple of days! Thanks!

[H500]

Russ, one word of warning... I believe the ATX supplies require certain connections to be made before they will turn on. I never used one for anything other than a computer so I can't say for sure.