Electronics Advice

[roofman]

I have 2 large 9"x4" electro magnets that ime using for a project at home..they are rated at 207vdc. Ive been driving them with 35vdc as thats all i can achieve and allthough still very strong at that voltage they will be monsters with 207 volts running through them,so my question for our Electronic heads is whats the best and most reliable way to convert 240acv to 207dcv?? ime thinking something along the lines of a DC motor speed controler..is this right? Cheers.

 

[DanielW]

I have 2 large 9"x4" electro magnets that ime using for a project at home..they are rated at 207vdc. Ive been driving them with 35vdc as thats all i can achieve and allthough still very strong at that voltage they will be monsters with 207 volts running through them,so my question for our Electronic heads is whats the best and most reliable way to convert 240acv to 207dcv?? ime thinking something along the lines of a DC motor speed controler..is this right? Cheers.

Look for a variable DC bench power supply,the amps will play a good part in how well the perform?

A power supply from a tread mill runs at about 180v DC

 

[roofman]

Look for a variable DC bench power supply,the amps will play a good part in how well the perform?

A power supply from a tread mill runs at about 180v DC

Now that seems ideal...cheers buddy
BTW where are you in M/side? ime Wirral.

 

[DanielW]

Now that seems ideal...cheers buddy
BTW where are you in M/side? ime Wirral.

Someones got to live there,I'm on the other side.

If you can find a treadmill on ebay that has a knackered motor you'll find the power supply will have a variale controller ,bit of tinkering and the supply should be able to get you 200v DC.

 

[roofman]

Someones got to live there,I'm on the other side.

If you can find a treadmill on ebay that has a knackered motor you'll find the power supply will have a variale controller ,bit of tinkering and the supply should be able to get you 200v DC.

Yiss...my thoughts too,ta.

 

[MattF]

For something like a magnet, you'd probably be better off staying old school and getting either a transformer which is thereabouts else using something like a variac. Variac is better as it is, as the name suggests, variable output. Then, just rectify the output from whatever you use with a full wave bridge rectifier to get your DC.

 

[500e]

Remember high voltage DC is nasty stuff it gets hold & don,t let go Take all safety precautions

 

[skotl]

You really need to start with an isolating transformer because a rectified DC voltage directly from 240V mains will be "hot" (i.e. several hundred volts from earth) on both poles.
If I wanted to do this (and I don't!), I'd start with a big yellow builder's 110V isolating transformer, then add a bridge rectifier to it. Converting 110VAC to DC gives you around 160VDC which, while not being 207V, is still the safest* way of getting a few hundred volts DC.

(* I use "safest" in terms that this is less dangerous than simply transforming and rectifying mains voltage - it's still not safe...)

 

[simplysimon]

what about an old oil DC stick welder with 200v output, you would have adjustable power

 

[normspanners]

Not sure a tread mill ps will have the capacity to run the magnets, what current do they draw?,

 

[ajlelectronics]

Best idea so far is the 110V site transformer. That will give isolation, somewhere near the best voltage and should be beefy enough to provide the current required. Also freely available of course at reasonable cost.

 

[DanielW]

Not sure a tread mill ps will have the capacity to run the magnets, what current do they draw?,

Well if you think about it some people are pretty heavy,I would imagine the motor takes some strain will it not.

 

[DanielW]

Specs on the treadmill motor I have is.....

180v DC
6 Amps
1.7hp

 

[normspanners]

1KW ish from it then, that prob will do it.
the magnet on the cranes at the scrap yd were big and had 220 dc 4-5 kva belt driven gennys with welding cable down boom to supply current.

 

[Robotstar5]

the magnet on the cranes at the scrap yd were big and had 220 dc 4-5 kva belt driven gennys with welding cable down boom to supply current.

The magnets on the yardcranes at the foundry were just over a ton, DC was supplied by a motor - generator set mounted on the bridge, the drawn arc on the DC contactors was impressive if you left the flashguards open.

 

[skotl]

5kVA 110V site transformer, currently at £20; http://www.ebay.co.uk/itm/5-KVA-Sit...al_Components_Supplies_ET&hash=item4d2645ac7d

Others selling them at a fixed price of circa £70.

 

[DanielW]

Cheaper to buy a used treadmill,almost all the treadmills are 180v DC

 

[MattF]

Cheaper to buy a used treadmill,almost all the treadmills are 180v DC

It's nothing to do with cheapness of parts. It's the safety factor, (and for good reason), which others are suggesting the isolation transformers for.

Personally, either way would be my opinion. Isolation is always a bonus, but it can also lead to an indifferent approach with regard to safety, to a degree. That's why I've always preferred working live on test benches. You never make the mistake of assuming isolation is in place that way.

 

[roofman]

Thanks for all the advice guys and everything taken onboard...I dont fancy turning my workshop into the electric chair cell like in Shawshank Redemption..LOL so leaning towards the 110V transformer which i have a few(my trade) so can anyone provide an explanation how to convert to DC (bridge rectifier ect) or whatever is needed.the mags are rated at 7 Watts.

 

[skotl]

You mean 7KWatts, right?

Have a look here http://uk.rs-online.com/web/c/?sra=oss&r=t&searchTerm=bridge rectifier&x=0&y=0 (bottom of page).

The 200V / 25A one is 5KW, and there's a 200V 35A (7KW) for less than a fiver. I'd be inclined to get the 1200V 25A one - for the sake of £8 it should be able to handle it no problem.
The two terminals marked ~ are the AC in, and then the +/- terminals are the DC out.

There will be a hell of a bang if you get this wrong, so take care! 5KW connections need to be rock solid, too - any loose connections will likely spark...

Edit: Go for this one, as most of the rest have a minimum AC voltage of 200V;
http://uk.rs-online.com/web/p/bridge-rectifiers/6296358/