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phoenix87 24th May 2012 07:34 AM

hi all,
I own a small battery charging shop, and we have to charge many car batteries. Before we used transformer based charger they were reliable but bulky and nt many features were avaible on then so we moved on SMPS based chargers. SMPS chargers are good and many features avaiable but they keep on failing if the charge current is very high or battery have short inside them.
In the last 8 month I have replaced 4 Smps based charger . Iys has become a annoyance for me .
I would like to bulid a SMPS based charger on my own.

phoenix87 24th May 2012 08:14 AM

this is my requirenent......
230- input
24V @ 200A
48V @ 100A

Short circuit protection....and over current protection is a must.
I have doing some reading on my own and have recently build a 500W half bridge smps on my own but jumping ffrom 500W to 5KW is long way to go on my own .So I would like some advises on hw to make the 5KW charger.....


PChi 24th May 2012 08:56 AM

You need more than short circuit protection and over current. It needs to be stable in constant current mode unlike most power supplies where the current limit is just protection.

I guess that you are using a 3 phase input? Do you need power factor correction? I guess that size and weight isn't a limitation.

Do you know why the previous SMPS chargers failed? They are not as tolerant of mains over voltage or transients as transformer based chargers.

I guess that a full bridge with current mode control would be the way to go. The high power level will mean that a custom made coil former wil be required. The transformer secondaries could use copper strip which will be a challenging to wind.

phoenix87 24th May 2012 10:45 AM

no most of chargers were single phase ..... Does it need to be 3 phase ???
I would prefer it to be single other wise i have apply for new 3 phase connection which will be costly.
PFC wont be needed I think .....

can I use hard switching for the battery charger...... cause Resonant converter are a bit diffcult to design....??


Pafi 24th May 2012 10:59 AM

On single phase 5 kW power hardly goes through without PFC.

But for battery charging pulsating current is OK, so if you can control the charging current proportional to square of the input voltage, the input current will be sinus-like. Big input puffer capacitor can be omitted then.

I prefer resonant, but you are right, it's not easy to control.

phoenix87 24th May 2012 11:41 AM

As far as I know Reasonant converter increase efficiency of the I have never tried resonant converter I dont know how increse in efficeincy is seen as far as hard switching converter is conserned I have achieved 87% percent efficiency .

for 5kw at 50khz is etd59 enough.....???


PChi 24th May 2012 12:16 PM

At 5 kW I think that typically in the UK it would use a 3 phase supply. The largest power supplies that I have worked on were 3 kW and used a 3 phase input. I don't know what typical wiring installations in India are like so I don't know what is best. I have worked on Mobile Phone Chargers and the mains voltage stability in India gave problems.

From memory the efficiency of the 800 W battery charger that I designed was around 90 % using hard switching.

I agree that a resonant converter could be difficult to design. The charger load is difficult because it varies from 0 to a short for a faulty battery.

I used two E65 cores per forward converter for 800 W which was conservative, ETD didn't exist then. An ETD59 sounds small making it difficult to wind enough copper around. I assume that this is a one off unit so ease of design and assembly is more important than efficiency, size and component cost so the transformer can be larger than necessary.

I wish you all the best with an ambitious project.

Pafi 24th May 2012 03:21 PM

ETD59 is too small for 5 kW, unless you use a very strong forced cooling.

With resonant PSU and 3 phase input 95 % efficiency can be reached at 48 V output, a little less at 24 V. But the features you need can be more difficult to implement.

With synchro-rectifier 95 % can be done at lower voltages also.

I suggest building more smaller blocks than 1 big.

Osvaldo de Banfield 24th May 2012 06:05 PM

Why not to return to old thyristor circuits? They are very reliable.

phoenix87 26th May 2012 04:05 AM

can any body show me some circuits for a 5kw SMPS based battery charger...


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