PSU Parallel Help

[SkippyDogg]

Hi,

I recently purchased a car amp for home use. ( seems to become a fad now a days ) and the problem is that the amp requires 48A. I have two identical power supplies ( same manufacture , brand , watts, etc) they are both 25A on the 12V rail. I would like to know how to wire them " parallel " so combined it would be giving my amp 50A. Thanks

[dtproff]

This one is almost imposible to do easily. The best method is to buy power supplies that were designed to be paralleled. Typically these are an n+1 configuration and the cheaper ones (without a dedicated chare signal) would probably incorporate droop sharing.

Here's the basic problem. The power supply with the lowest voltage takes the current. The more you load the psu the more the voltage drops in the wire so once it starts to sag, it quickly can hit it's internal current limit and shut down. As soon as it shuts down the second PSU becomes fully loaded and will also shut down.

There are acouple ways or forcing the split but at those current levels you don't want to make a mistake.

You might consider splitiing the load between the two power supples as an alternative.

Sorry... I know I wasn't much help.

Tony

[SkippyDogg]

Originally posted by dtproff
This one is almost imposible to do easily. The best method is to buy power supplies that were designed to be paralleled. Typically these are an n+1 configuration and the cheaper ones (without a dedicated chare signal) would probably incorporate droop sharing.

Here's the basic problem. The power supply with the lowest voltage takes the current. The more you load the psu the more the voltage drops in the wire so once it starts to sag, it quickly can hit it's internal current limit and shut down. As soon as it shuts down the second PSU becomes fully loaded and will also shut down.

There are acouple ways or forcing the split but at those current levels you don't want to make a mistake.

You might consider splitiing the load between the two power supples as an alternative.

Sorry... I know I wasn't much help.

Tony

O i see , well do you know how split them like you said ?

[ifrythings]

Originally posted by dtproff


Here's the basic problem. The power supply with the lowest voltage takes the current.
Tony

You have that backwards, the powersupply with the higher voltage will do all the work, the way you explained it is for semiconductors

[Eva]

Is the otput voltage adjustable? Some models have a trimmer with a narrow range, like 11V to 14V. This allows for voltage matching. Current sharing may be improved by wiring the power supplies to the amplifier through equal lenghts of not too thick wire, its resistance will help to improve current sharing. For example, a 1 meter run of 12AWG (actually 2 meters) will result in approx .010 ohms and .25V drop for 25A.

[SkippyDogg]

Originally posted by Eva
Is the otput voltage adjustable? Some models have a trimmer with a narrow range, like 11V to 14V. This allows for voltage matching. Current sharing may be improved by wiring the power supplies to the amplifier through equal lenghts of not too thick wire, its resistance will help to improve current sharing. For example, a 1 meter run of 12AWG (actually 2 meters) will result in approx .010 ohms and .25V drop for 25A.

I don't think the output voltage can be adjusted. I have 8AWG wire that will be from the power supplies to the amplifier; Is that good enough ? Also i won't be using 2 meter the distance from the amplifier to the power supply is about 5 ft.

[Eva]

Current sharing will be better if you use a not so thick wire. I'm not sure if you understood my explanation about independent runs of wire from each power supply to the amplifier.

This uses wire resistance to improve current sharing, and AWG12 will work better without causing too much voltage drop (it's a compromise). It will easily accomodate .05V to .1V of difference in output between power supplies without forcing one of them to do all the work.

AWG8 will result in much less tolerance to differences in output voltage.

[SkippyDogg]

Originally posted by Eva
Current sharing will be better if you use a not so thick wire. I'm not sure if you understood my explanation about independent runs of wire from each power supply to the amplifier.

This uses wire resistance to improve current sharing, and AWG12 will work better without causing too much voltage drop (it's a compromise). It will easily accomodate .05V to .1V of difference in output between power supplies without forcing one of them to do all the work.

AWG8 will result in much less tolerance to differences in output voltage.

Ooooo i see. Well , can you please tell me how to share the current? If you know how. Thanks

[dtproff]

Ifrythings... Thanks for the correction. I was in china when I wrote this and had some fuzzy thinking. You were absolutely correct. Thanks.