London Fixed-gear and Single-speed SJS Cycles

bigben · 10th May 2009

Hello Peeps,

Two questions for the knowledgeable amongst you:

1. If I combine all the 12v outputs from a 450 watt ATX psu what sort of amps can I expect? Need to power a load of wiper motors and not sure how many I can squeeze out of each psu.

2. In order to get a full 12v from said ATX psu I need to also load the 5v output, an american web site says to use a 10 watt 10 ohm wire wound "sandbar" load resistor, can anyone confirm if H10R on this link is the right one?

http://www.maplin.co.uk/module.aspx?moduleno=2181

Thanks,

Ben

danb · 10th May 2009

pretty sure you will need something beefier than a pc psu to power wiper motors (as they have massive torque)

bigben · 10th May 2009

Motor draw under load is about 8 amps at 12v (rising to about 14 if stalled), just a question of what proportion of the 450w is 12v.

Bobby Dids · 10th May 2009

Questionable maths, but I'd say in theory you could drive 3 motors off 35ish amps available. That's in theory. That's also alot of juice. You've not mentioned starting current, if they're all starting at once that might pop your psu.

Fuck it, give it a go. H10R looks fine for the 5V load.

bigben · 10th May 2009

Many thanks.

Reckon I might stick at two per psu thus hopefully giving myself a cushion.

lucas · 10th May 2009

450 watts....

so having 12v you should have 37. 5 amps ???

EDIT: using P = IV

danb · 11th May 2009

atx psu power ratings are notoriously overspecced - 450w is probably closer to 300w real world and along with the fact that you have multiple voltage rails the actual output on the 12v rail is prob around 10A - so possibly doable but I would be inclined not to if as you say there is any chance the motor will stall - but bear in mind IANAEE

bigben · 11th May 2009

Quote:

Originally Posted by danb

but bear in mind IANAEE

Excuse my dumb, but what does that mean? I ordered 13 x 450W today, I'll see how they run, I can always go one per psu if needed.

danb · 11th May 2009

i am not an electrical engineer :)

TheBrick(Tommy) · 11th May 2009

Multigrooves has a E.E degree I think

bigben · 17th May 2009

Hmmmmmm

Buggerdoubledoo.

So I've converted a psu as per here:

http://web2.murraystate.edu/andy.bat...owersupply.htm

It will run a wiper motor set up as I'll need it, however if I try to have two starting at the saem time they both stall. Stagger the start up and both will run (although the 2nd is just sitting on the bench with no mechanism attached so minimal load), guess I'm on one per motor.

Sigh.

10th May 2009	#1
bigben	Off topic, anyone good at electronics? Hello Peeps, Two questions for the knowledgeable amongst you: 1. If I combine all the 12v outputs from a 450 watt ATX psu what sort of amps can I expect? Need to power a load of wiper motors and not sure how many I can squeeze out of each psu. 2. In order to get a full 12v from said ATX psu I need to also load the 5v output, an american web site says to use a 10 watt 10 ohm wire wound "sandbar" load resistor, can anyone confirm if H10R on this link is the right one? http://www.maplin.co.uk/module.aspx?moduleno=2181 Thanks, Ben
	quote reply

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10th May 2009	#2
danb	pretty sure you will need something beefier than a pc psu to power wiper motors (as they have massive torque)
	quote reply

10th May 2009	#4
Bobby Dids	Questionable maths, but I'd say in theory you could drive 3 motors off 35ish amps available. That's in theory. That's also alot of juice. You've not mentioned starting current, if they're all starting at once that might pop your psu. Fuck it, give it a go. H10R looks fine for the 5V load.
	quote reply

10th May 2009	#6
lucas	450 watts.... so having 12v you should have 37. 5 amps ??? EDIT: using P = IV
	quote reply

11th May 2009	#7
danb	atx psu power ratings are notoriously overspecced - 450w is probably closer to 300w real world and along with the fact that you have multiple voltage rails the actual output on the 12v rail is prob around 10A - so possibly doable but I would be inclined not to if as you say there is any chance the motor will stall - but bear in mind IANAEE
	quote reply

11th May 2009	#10
TheBrick(Tommy)	Multigrooves has a E.E degree I think
	quote reply

17th May 2009	#11
bigben	Hmmmmmm Buggerdoubledoo. So I've converted a psu as per here: http://web2.murraystate.edu/andy.bat...owersupply.htm It will run a wiper motor set up as I'll need it, however if I try to have two starting at the saem time they both stall. Stagger the start up and both will run (although the 2nd is just sitting on the bench with no mechanism attached so minimal load), guess I'm on one per motor. Sigh.
	quote reply

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