# Basic power supply questions

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Hello,

A back to school type question. If I get a bench power supply that has a 200W 13.8DVC spec, and connect a 'thing' that is rated at 12VDC and 5A, - then is that ok ?

I am assuming the voltage will be fine, but am I correct in thinking that the device will only pull a maximum of 5A.

If the power supply only has one output then I presume all 'things' I connect need to connect to the outputs.

Basically I have 4 things that use the 12V 5A cigarette lighter attachments, and I want to replace this with a bench power supply. Any recommendations at to what would work much appreciated. Something from Maplin I guess ?

Thanks

Alistair

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If my maths is correct the psu is rated at 14.5 amps. If the total current draw is less than 14.5amps then all is well.

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Perhaps one of these.

Just make sure the devices connected can handle the 13.8v and the Max draw of the 4 items connected does not exceed the psu specs.

I expect you may get a few suggestions saying use a separate supply for the mount and run the others from another supply. The mount will draw more current when you slew it than when it rotates at standard speed.

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The basic maths is watts=volts x amps so your 'thing' want to use 60 watts whereas, as already stated, your power supply is rated @ 14.49 amps

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Ahh, but he wants to use 4 things at once

The cables are for 5A at around 12-14v but not all of the 'things' may need to draw that much.  If you know the max requirements of the things it will be easier to make sure you have the right supply.

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17 hours ago, AlistairW said:

Hello,

A back to school type question. If I get a bench power supply that has a 200W 13.8DVC spec, and connect a 'thing' that is rated at 12VDC and 5A, - then is that ok ?

It depends a lot on "the thing".

If your "thing" is resistive in nature, like for example a dew heater, then supplying it with a 15% higher voltage means it will draw 15% more current and therefore consume 32% more power.

However if your "thing" contains an in-built regulator to supply an internal "sub-thing", then either it would draw 15% less current, being a modern power supply OR it would draw the same current and get hotter if it's power supply was low-tech.

But

I'd be somewhat skeptical about the claimed power / current output of a lot of power supplies. The quoted X Amps might only be for a short period (read the small print). It is also worth noting that the contacts inside those cigarette lighter connectors aren't the greatest and can become intermittent over time - especially if outside and inserted / removed frequently. This is due to corrosion, thin metal, sparks as the contacts are made and low quality mechanical (not soldered) connections inside the connectors themselves.

If your "things" really do need 5 Amps, then I'd suggest de-rating (i.e. aquiring kit that claims to work  at 10 Amps, etc.) the spec.s of whatever power supply, connectors and cables you use by at least 50% for reliability.

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Thanks for the replies. I just want to be double sure, as I am about to make some purchases. If I have 1 thing rated at 12V and 5A and I buy a bench power supply rated at 1000W at 12V - then I will be fine. The 'thing' will only 'pull' the amount (of current) it requires. So the Voltage is important but the Wattage ratting just has to be sufficient (60W in this case), or over. Is that right ?

Thanks

Alistair

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