Author Topic: high power DC/DC converter  (Read 967 times)

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Offline V_King

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high power DC/DC converter
« on: July 04, 2017, 07:28:12 am »
Hello,
My work place is decommissioning a number of 3kW UPS units.
I want to reuse them as inverters to supply 230V for my boat hooked to the deep cycle leisure batteries.
I did some digging, there is plenty of projects of this kind online using small UPS units. I would need to sort out a better cooling for the unit to be run for prolonged periods which is easy. I am not worried about the charging side as the batteries are charged by the solar panels and diesel generator.
The problem I have is that the UPS units use 10x 12V batteries connected in series to provide the 120VDC nominal to the UPS. I do not want to use more than 5-6 batteries due to space constraints and thinking of a DC/DC converter to pretty much double the voltage from 60VDC to 120VDC. 
There are lots of small DC/DC integrated units up to a couple of hundred watts. but I need 3kW rated one.
I wonder if I can run in parallel a number of those DC/DC converters? Or are there any other simple ways of doubling the DC voltage?
Cheers
 

Offline Fungus

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Re: high power DC/DC converter
« Reply #1 on: July 04, 2017, 01:15:17 pm »
I wonder if I can run in parallel a number of those DC/DC converters?

No. Those things monitor their output voltage closely. Even a tiny difference in tolerances means they'll fight each other over the 'correct' voltage and some of them will be overloaded.
« Last Edit: July 04, 2017, 05:43:13 pm by Fungus »
 

Online Zero999

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Re: high power DC/DC converter
« Reply #2 on: July 04, 2017, 01:38:31 pm »
Higher voltages mean less current and greater efficiency so reducing the voltage is counter-productive. Use ten 12V batteries with half the Ah rating and they should take up the same amount of space as 5 larger ones, everything else being equal of course.
 

Offline Supercharged

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Re: high power DC/DC converter
« Reply #3 on: July 04, 2017, 02:11:22 pm »
Higher voltages mean less current and greater efficiency so reducing the voltage is counter-productive. Use ten 12V batteries with half the Ah rating and they should take up the same amount of space as 5 larger ones, everything else being equal of course.
,
I would also add that, should you put a DC/DC converter between the UPS and its batteries you bypass the battery undervoltage protection built into the UPS. You could therefore damage the batteries by discharging them too far without noticing.
Science is about what is, engeneering is about what can be.
-Neil Armstrong
 

Offline David Hess

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Re: high power DC/DC converter
« Reply #4 on: July 04, 2017, 04:02:04 pm »
I would also add that, should you put a DC/DC converter between the UPS and its batteries you bypass the battery undervoltage protection built into the UPS. You could therefore damage the batteries by discharging them too far without noticing.

That is not necessarily the case.

Instead of trying to design a regulating 3 kilowatt switching power supply to convert 4x12V to 10x12V, it would be much simpler to design a 3 kilowatt inverter.  Open loop operation means that the output voltage will track the input voltage minus losses.  An inverter also places fewer demands on the input and output capacitors.

Now the big problem becomes finding or building a suitable medium to high frequency transformer.  If I did not wind the transformer for 20+ kHz operation, then I would use several 60Hz transformers in parallel at a slightly higher frequency if I could find the right voltage and ratio.
 


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