Re: battery charger topology
- From: MooseFET <kensmith@xxxxxxxxx>
- Date: Tue, 29 Jan 2008 21:06:16 -0800 (PST)
On Jan 29, 6:29 am, reggie <veggie...@xxxxxxxxxxxxxx> wrote:
Hi all,
My battery charging knowledge is limited, but I know a bit about SMPSU
design.
I was wondering what topologies and silicon could be used to deliver
substantial powers used to charge a 300Ah 24V lead acid battery bank
(employing three stage charge curve like :-http://www.electroparts.com.au/images/bc_chart_large.jpg).
I have thought:-
1) Front end boost circuit, to give unity PFC and constant voltage
over wide input voltage range
This is a good way to go. Since battery charging doesn't need ripple
free current, you don't need the huge storage capacitors you would
normally have to build into the design.
The down side of making a booster that produces a constant voltage is
that you have to design for both the low line and high line cases.
The high line case, sets the voltage you must boost to. The low line
sets the current in the transistors.
At these high power levels, you may be better off letting the current
peak mains voltage set the booster's output voltage.
1.1) But have read that due to high peak currents can be unusable at
powers above 150w (onsemmi switch mode PSU reference manual SMPSRM/D
rev 3B July 2002 page 9)
I think they've set that point a little low. You can get some really
amazing transistors these days. I would still question going over a
few hundred Watts with just a simple booster design.
1.2) Should I parallel up boost circuit or go to duel-phase for higher
powers (not just components entire circuit)
If you are going with a booster design, I would suggest that you go 3
phase or perhaps even 5 phase. More phases makes it much easier to
keep the ripple current of the booster out of the input circuit. You
are going to end up with some fairly large (physically) inductors in
the design.
1.3) What effect would the input frequency swing have on the boost
circuit?
Within reason, changes in the mains frequency have no great effect.
The lowest frequency is considered in the size of the storage
capacitors,
2) Probably a full isolated bridge with synchronous rectification.
At 24V the advantage of synchronous rectification is just about gone.
If you do go this way, I suggest you put large schottky recifiers
across the rectifier MOSFETs. This reduces the losses at the switch
off point. Normally you either end up with the MOSFET conducting
backwards briefly or its substrate diode takes a pulse of current.
With the large schottky diodes, you can error in favor of turn the
MOSFET off a bit too quickly and not have substrate recovery time
causing losses.
3) what effect does the three stage charge cycle have on output
voltage and current the PSU supplies (told you I don't know much about
battery charging)?
You are just making a "variable power supply" and then varying it
based on the battery.
4) Are there any good guides for designing lead acid battery chargers
within this power range?
Buy a face shield.
5) any application guides / circuits on the net for this type of
application?
specification:
Input voltage: 90 - 260 VAC RMS
Input frequency: 40 - 100 Hz
Nominal output power: 600 W +/- 5%
Nominal output current: 25 A
Rated battery voltage: 24 VDC
Operating amb. temperature: -25ºC to +40ºC
Efficiency: >85%
Cooling: forced air and none forced air
Package:187mm x 116mm x 50mm
.
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