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tricklidz
01-02-2014, 07:00 PM
Hi all,
Made a setup to power the table on my mill using a 12v automotive wiper motor. I'm now running it through a motorcycle battery with a battery tender (charger). Would like a more permanent/neater solution. Been looking at converters and would like at least 20amp rating. The speed controller is 20a and the motor is rated for 15a. Any suggestions?

lakeside53
01-02-2014, 07:11 PM
Lots of stuff available - like this : http://www.ebay.com/itm/110V-120V-220V-240V-AC-to-DC-Converter-12V-30A-/370352140943?pt=LH_DefaultDomain_0&hash=item563ab5328f

Mike Amick
01-02-2014, 07:21 PM
Hey lidz .. what kind of controller ?

tricklidz
01-02-2014, 10:21 PM
Hey lidz .. what kind of controller ?
Cheap Chinese one. Ebay.

darryl
01-03-2014, 01:17 AM
Electrolytic caps will age and lose value, but this happens quicker and will have worse results in a switching power supply vs a 'brute force' transformer/rectifier/filter. Largely for this reason I stay with the traditional approach when I build a power supply that I want to last. The capacity value needs to be much larger at 60 hz than at some high switching frequency, but the cost isn't really much greater. The transformer based 60 hz power supply will be heavier and larger, but what would that matter- and dc motors don't much care if there's some ripple on the output voltage. As well, they are capable of delivering a higher than normal current for short periods, and don't have any mysterious shut-down characteristics that a switching power supply might have.

Any controller you find will likely be a pulse width modulator of some sort, and will work fine with this.

12V power supplies are made for car audio displays, and come in various current ratings. Something capable of 20 amps would be a relative lightweight. The newest ones are likely to be switching power supplies, but you might be able to find an older one for cheap. They are likely to be regulated as well, which might serve you well in some future applications, if not now. I don't think you really need regulation if you're working through a controller anyway.

You might even find a basic battery charger that would serve, though for the most part these days they have mini-brains which might prevent them from outputting if they don't see a voltage to start with. You can bypass this, but you'll need some electronic knowledge to get the job done. If you find a charger that works, is heavy, and has the current capability, you can use that as the start of your power supply project. For the most part you'd only have to add an electrolytic filter cap.

C_lazy_F_Guns
01-03-2014, 05:16 AM
Most old junk campers have pretty nice converters in them to run the 12v lighting and water pump when on shore power, they can often be had for about nothing. I have one that runs a bunch of stuff in my shop, mine even has a built in battery charger that comes in handy.

GEP
01-03-2014, 07:25 AM
You can find a junk desktop computer and remove to ATX power supply and build you a power unit cheap.
I have some instructions on how to do it but cant attach them here. You can send me your e-mail if you like i will send them to you. Yes you can buy them on e-bay butdon'tt forget to look at the shipping cost
Can you post a pic of your power feed

dian
01-03-2014, 09:48 AM
this is half the price, but they still are expensive, i mean thats only 360 watts.

http://www.ebay.com/itm/110-220V-to-DC-12V-24V-40-60-180-360W-LED-Strip-Light-Switch-Power-Supply-Driver-/300937785421?pt=US_Lighting_Parts_and_Accessories&var=&hash=item46114a304d#ht_9651wt_1187

Stern
01-03-2014, 09:52 AM
Did the same on my mill, and simply got a 12V transformer, bridge rectifier and some filter caps. Makes a nice 12V power supply with fairly steady DC. Then bought a PWM from China (about $4.00) as a speed control .... works great.

DICKEYBIRD
01-03-2014, 10:56 AM
Did the same on my mill, and simply got a 12V transformer, bridge rectifier and some filter caps. Makes a nice 12V power supply with fairly steady DC. 12V through a bridge would be about 16V, yes?

Fasttrack
01-03-2014, 01:15 PM
Electrolytic caps will age and lose value, but this happens quicker and will have worse results in a switching power supply vs a 'brute force' transformer/rectifier/filter.

That depends largely on the design and component choice. A high quality switched mode power supply can last for decades. A cheap Chinese one might last a couple of years if you don't tax it too hard.

:)

Ripple current and heat are what kills aluminum electrolytic capacitors. In switched mode power supplies, the ripple currents can be very large. With a "brute force" design, the ripple current tends to be much lower.

tricklidz
01-03-2014, 01:23 PM
You can find a junk desktop computer and remove to ATX power supply and build you a power unit cheap.
I have some instructions on how to do it but cant attach them here. You can send me your e-mail if you like i will send them to you. Yes you can buy them on e-bay butdon'tt forget to look at the shipping cost
Can you post a pic of your power feed
Here's all the info from my blog-
http://www.blogger.com/blogger.g?blogID=5105533485007169300#editor/target=post;postID=8271191576908474692;onPublished Menu=allposts;onClosedMenu=allposts;postNum=0;src= postname

Fasttrack
01-03-2014, 01:56 PM
12V through a bridge would be about 16V, yes?

A 12 volt peak input would result in an output that is 12V - 2*Vf where Vf is the forward voltage drop of the diodes. Typically values range from 0.7V to 1.5 volts per diode. If you measure RMS voltage, than you can convert that to Vp by multiplying by ~1.4 (or the square root of 2).

So, 12 Vrms = ~ 16.9 Vp. You then subtract the two diode drops. Lets assume a Vf of 1.2 volts. Then the output would be ~14.5 VDC.

Couple the 14.5V with a PWM controller meant for 12V and you'll never know the difference. :)

tricklidz
01-03-2014, 02:06 PM
Here's all the info from my blog-
http://www.blogger.com/blogger.g?blogID=5105533485007169300#editor/target=post;postID=8271191576908474692;onPublished Menu=allposts;onClosedMenu=allposts;postNum=0;src= postname
Updated blog with video
http://tricklidz.blogspot.com

GEP
01-03-2014, 03:13 PM
http://www.instructables.com/id/ATX-Power-Supply-gt-Cheap-Bench-Top-Power-Supp/
Here is a ATX power supply conversion

DICKEYBIRD
01-03-2014, 05:29 PM
A 12 volt peak input would result in an output that is 12V - 2*Vf where Vf is the forward voltage drop of the diodes. Typically values range from 0.7V to 1.5 volts per diode. If you measure RMS voltage, than you can convert that to Vp by multiplying by ~1.4 (or the square root of 2).

So, 12 Vrms = ~ 16.9 Vp. You then subtract the two diode drops. Lets assume a Vf of 1.2 volts. Then the output would be ~14.5 VDC.

Couple the 14.5V with a PWM controller meant for 12V and you'll never know the difference. :)I knew that.



(Not);)

darryl
01-03-2014, 06:06 PM
Regulated power supplies aside, most 'brute force' ones actually deliver from 14 to about 16 volts with no load. If you are going to regulate the output voltage, it makes sense to start with 20 volts, but if you just want to make sure you have at least 12V under full loading conditions, then start with 14-16 volts. None of the motors we're talking about here will care if the voltage is a little high. In a pwm or chopper circuit, the output device when fully on won't waste more than a volt or so, so there's essentially full voltage available to the motor when the output device is on. There may or may not be the need for a higher voltage to begin with, depending on the particular design. I'd suggest a good design of controller won't have this 'extra' voltage requirement.

That being said, you can then select a transformer with a secondary voltage rating of about 11 vac. That will be under load, so what you end up with is about 15 vdc after rectifier losses. That will drag down to about 12v under load, so it gets you into the right ballpark. If all you can find is a secondary rating of 12vac in a suitable transformer, that's fine.

If I recall, the power pack that used to come with rv's outputs about 16 volts with no load. It would be perfect for your application. If there's a failure mode in those, for the most part it's going to be in a relay contact or charge controller pc board- usually dirt, heat, or water related damage. I'm suggesting here that even a dead unit (which you could probably get free or cheap) would probably have a working transformer, and probably a good rectifier also. It may need a filter to make 'real' dc out of rectified ac.