• Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!

Run pump off 12v line?

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.

Sam__

Member
Joined
Mar 12, 2007
Location
UK
I have an american pump and live in the uk so I need some kind of transformer but before i go for a 240v to 115v on would it be viable to get a 12v to 115v one and wire it up to a PSU?
I could get one of those ones for the car and wire it to a molex.
I can hook up the seperate (if it needs to be) PSU to turn on when the main does easliy enough but I was just wondering if it was a viable option.
I have an Eheim 1250. (28W)

I could use sumthin like this. ebay item link but preferably one in the UK to save on postage lol.
All opinions are welcome.thanks in advance.
 
Umm 12V vs 115V. Sorry but the 12V from a PSU is DC and the 115V is AC. DC does not work on a transformer, nor will a xfmr change 12VDC to AC.

Edit: Yea you will need something like that. Or to go from 220 to 115, the xfmr you need is small wattage, should be cheap as long as the pump handles 50hz instead of 60hz. If it can't the inverter is your only choice to give you 60hz. Good luck finding a 60hz converter there.
 
Umm 12V vs 115V. Sorry but the 12V from a PSU is DC and the 115V is AC. DC does not work on a transformer, nor will a xfmr change 12VDC to AC.

Edit: Yea you will need something like that. Or to go from 220 to 115, the xfmr you need is small wattage, should be cheap as long as the pump handles 50hz instead of 60hz. If it can't the inverter is your only choice to give you 60hz. Good luck finding a 60hz converter there.

thanks a lot....i will look into it.

also...u got any idea how efficient the inverter would be?

just looked at the pump and it needs 60Hz so i guess im gunna have to use an inverter.

edit: another Q...can i use one of those in car inverters which are rated at like 75W? should work in theory but just making sure.
 
Last edited:
so if its 90% efficient then I should (in theory) be able to run it of a PSU...
 
You don't need an inverter, any and all pump can run at lower Hz, the nominal speed of the electric motor will decrease with lower frequency tho, but will keep a decent torque. This is use alot on higher hp pump actually (google "VFD" or variable frequency drive).
 
You don't need an inverter, any and all pump can run at lower Hz, the nominal speed of the electric motor will decrease with lower frequency tho, but will keep a decent torque. This is use alot on higher hp pump actually (google "VFD" or variable frequency drive).

oh kwl..thanks.

I am liking the idea of running the pump off a PSU just to have the failsafe of it turning on when the rest of the comp does.
Will it work?
240v>PSU>12v>inverter/transformer>115v>pump.

Im thinking of getting one of those in car ones for the 12v to 115v convertion - Ebay linky -....will it work?
 
Yes, it will, but it would probably be cheaper to have the pump turn on with the comp via a relay, that's what I do. Then again, the inverter you linked to is cheap, but I doubt you'd get the 80% efficiency stated earlier with such a model, but then again, I doubt the pump consume that much energy, so the inverter's efficiency should not be such a big deal.
 
Yes, it will, but it would probably be cheaper to have the pump turn on with the comp via a relay, that's what I do. Then again, the inverter you linked to is cheap, but I doubt you'd get the 80% efficiency stated earlier with such a model, but then again, I doubt the pump consume that much energy, so the inverter's efficiency should not be such a big deal.

awesome!... I shall buy the inverter and put it all together as soon as i can. Unless anyone has a better idea.
The relay is a good idea I did consider it but that would mean buying another transformer and wiring up up and what no and i dont know much about using relays so i think the PSU>inverter>pump is my best option.
 
I would first try to simply connect a diode on the powercord. Have a look inside an electric shaver, when you flip the switch from 110 to 220v all you actually do is connect a diode in serial with the electric motor.
 
I would first try to simply connect a diode on the powercord. Have a look inside an electric shaver, when you flip the switch from 110 to 220v all you actually do is connect a diode in serial with the electric motor.

Interesting. U sure this would work???
 
I vote buy a new pump...


Blowing lots of money into a pump :)

Its only like a tenner to make this thing....and iv kinda already bought the inverter. Plug it should be a good learning experience. :D
 
I know I would try the diode thing, it will work like a Half wave rectifier, completely cutting off the negative cycle of the AC, 180 degrees of the phase is gone, leaving half the voltage as an "alternating DC". Dont let the DC thingy scare you too much, an AC electric motor will work as long as the current is ever changing, the negative cycle is not crucial to operation.

Already mentioned shavers, this method is also used in for example hair dryers, when you flip the switch to reduce the fan speed you are connecting a diode to remove the negative cycle, thus the electric motor receives only half the voltage.

Be sure to use a diode (or use 2 in series for redundancy) that can withstand 220v (or at least 110v), and while the power requirement will be less than 0.25 watts its always nice to be on the safe side, get diodes rated for 0.5 or even 1 watt.

Diodes has the bad habit that when they break they will often conduct electric current in both directions instead of breaking the circuit in both directions. A broken diode conducting in both directions is the same as no diode at all and you will then of course feed 220v to the pump.

Not a perfect or elegant solution but its so cheap that its a shame to not try :D A transformer setup will cost so much i would rather go for a new pump.
 
I know I would try the diode thing, it will work like a Half wave rectifier, completely cutting off the negative cycle of the AC, 180 degrees of the phase is gone, leaving half the voltage as an "alternating DC". Dont let the DC thingy scare you too much, an AC electric motor will work as long as the current is ever changing, the negative cycle is not crucial to operation.

Already mentioned shavers, this method is also used in for example hair dryers, when you flip the switch to reduce the fan speed you are connecting a diode to remove the negative cycle, thus the electric motor receives only half the voltage.

Be sure to use a diode (or use 2 in series for redundancy) that can withstand 220v (or at least 110v), and while the power requirement will be less than 0.25 watts its always nice to be on the safe side, get diodes rated for 0.5 or even 1 watt.

Diodes has the bad habit that when they break they will often conduct electric current in both directions instead of breaking the circuit in both directions. A broken diode conducting in both directions is the same as no diode at all and you will then of course feed 220v to the pump.

Not a perfect or elegant solution but its so cheap that its a shame to not try :D A transformer setup will cost so much i would rather go for a new pump.

You have convinced me. I shall try n find a diode of the right spec. Do you connect the diode to the +ve?

Edit: Would these work? Ebay linky
 
Those should do, 1 amp translates to ~0.7 watts.

Where is that +ve you are talking about? Alternating current has no + or -, it doesnt matter where you connect the diode physically, what you need to do is to find a place where you can cut a wire going to the motor, then connect the diode between there (where you cut the wire). As long as it is in series with the motor it doesnt even matter what way you put the diode. Then isolate bare metal to avoid unpleasant surprises in the future, and then finally plug the pump power cord into a 220v wall outlet for testing. If it goes faster than it did in the US something is wrong.
 
Those should do, 1 amp translates to ~0.7 watts.

Where is that +ve you are talking about? Alternating current has no + or -, it doesnt matter where you connect the diode physically, what you need to do is to find a place where you can cut a wire going to the motor, then connect the diode between there (where you cut the wire). As long as it is in series with the motor it doesnt even matter what way you put the diode. Then isolate bare metal to avoid unpleasant surprises in the future, and then finally plug the pump power cord into a 220v wall outlet for testing. If it goes faster than it did in the US something is wrong.

Oh yeah...Doi...

Isn't 1A @ 400V - 400W????
I can connect the diode in a transformer case I have which already has the plugs for UK and US so im not having to cut any cables :D.

I'll put the order in for the diodes tomoz when I have the time.

I didnt think the solution to this problem would be so simple...thanks.

A quick Q: would 3 diodes in a row help for even more redundancy? or is there a point where they effect the voltage or current? I've just started learning bout diodes in electronics lessons so want as much info as you can :D.lol.
 
Last edited:
Watts = Amps*volts

so yes, 1A at 400V is 400W


And diodes drop the voltage a little, I forget the technical name for it (I think its Vdrop) but it varies per diode.
 
I personally don't like the diode idea. Depending on the pump's design it may or may not work.
And as for redundancy, unfortunately if one were to fail closed (closed== circuit, open== no circuit) It would increase the voltage fed to the circuit, it is impossible for me to tell you exactly how much, because the diode will have a unique resistance, and that resistance determines how much voltage is added.
PS: It would turn the AC into a lop sided sine wave.



PS: It would be useful to know what pump you are using.


----IGNORE----
I would first try to simply connect a diode on the powercord. Have a look inside an electric shaver, when you flip the switch from 110 to 220v all you actually do is connect a diode in serial with the electric motor.

That only works for low current, and is called a half wave rectifier. In short, AC current is a Sine wave- the diode cuts the wave in half effectively halving the potential difference(voltage) with the side effect of halving the frequency.

Whoops.... Didn't see the post already mentioning this.
 
Last edited:
I don't think the diode is that good an idea, but I'd still try it :p
Also, Watts=Amp*Volts, but it's the voltage drop your looking at here, so th3 is right, 1 amp gives about 0.7W through a diode (roughly).
 
Back