topology suggestions for 3.5kW batt charger?

[colin]

I'm liking this idea of your's more and more, Colin. I found a 600W PC
power
supply with active PFC on eBay for $25, incl. shipping. That's definitely
cheap enough to play around with. Heck, the Litz wire I'll need for the
secondary will probably cost more than the power supply itself!



If an SMPS uses current mode control, though, paralleling two or more
together is trivial, even if Vo is high. I totally agree that no matter
what
the control scheme you are asking for trouble when you try to put supplies
in
series (dueling feedback loops).



That's the truth, and the components that blow up tend to be expensive
ones...




This was precisely my reasoning for just going with a straight boost PFC
design.

Thanks for the input - I'm definitely going to try this on one supply even
if
the total output from one PC supply isn't enough to make a practical
charger
(I need to keep the total charge time for the two banks under 12 hours for
it
to be at all practical, which means I need at least 2.6kW). Still, as a
quick
and dirty charger it has lots of merit (and it will be isolated, anyway).

If you can access the individual batteries in the packs it might be doable
with lots of them.

or if you can modify one of the secondary windings to give you the volts you
need and leave the primary untouched.
ofc the output stage wont be built with the clearences for 264 v

I made a battery charger out of a computer psu, threw away all but the 5v
output and upgraded the input switch so it was capable of giving enough
voltage. modified the current limit too,
you still need to know what your doing though, but it can save some trouble
debugging the primary side.

even if it doesnt its usfeull for parts, especialy if it has a nice big
transformer.

Colin =^.^=

 

[MooseFET]

Fair enough. Still, with no prior art to study one would have a lot of pain
and misery to look forward to before getting a new topology working, much
less optimized.

For a low power case, this would be fairly easy to get working. At
many KW, all designs will be hard to get working. Remember that I did
say I posted it "just for fun". It, I think is a cute idea because it
is so well suited to doubling the voltage which it just happens is
about what you need.

What I meant by this is that a short circuit will not cause immediate
destruction of the switch(es). L1 will saturate, of course, and a circuit
breaker will trip, but once the short is removed and power restored the
circuit should resume operating.

The output diodes will take it on the chin if there is a short. The
circuit will be quite broken as a result.

I still think you could probably use half of the outputs of a phase-shifted
full bridge controller IC to manage this topology (eg - UCC3895).

I think it would take more parts to do it with one of them than
without. The output drive would not be enough to drive the needed
MOSFETs, there is no good way to make the overlapping drive and it
needs a forest of parts to make it happy.

The LT3827 looks easier to talk into making the needed waveforms.

I'm sure someone will point out that a PIC can do it much easier.

 

[Tesseract via ElectronicsKB.com]

I made a battery charger out of a computer psu, threw away all but the 5v
output and upgraded the input switch so it was capable of giving enough
voltage. modified the current limit too,
you still need to know what your doing though, but it can save some trouble
debugging the primary side.

Well, my attempt to dismantle the transformer from a cheap-o CompUSA power
supply last night met with total disaster. The, one detail we both seem to
have forgotten is that commercial switchers tend to have their transformers
dipped and/or vacuum impregnated. Needless to say, when I tried to separate
the core halves I ended up breaking the ferrite into lots of little pieces....
This does not bode well for re-winding the transformer on this beast:

http://www.weirdstuff.com/cgi-bin/category.cgi?item=22081

An otherwise excellent choice! Only $100 and you get yourself an honest 3kW
of 48V output. I'll probably buy one anyway and hope it uses a PQ44040 core
(as I have those in stock). The education one can glean just from taking
something like this apart is worth the price of admission!

-Jeff

 

[Tesseract via ElectronicsKB.com]

The output diodes will take it on the chin if there is a short. The
circuit will be quite broken as a result.


The LT3827 looks easier to talk into making the needed waveforms.

I'm sure someone will point out that a PIC can do it much easier.

I took a look at the LT part and agree it would be ideal for producing the
right gate drive signals, however, it is expecting to control a buck
regulator and the KenSmith idea certainly ain't one of those. Closing the
loop, then, might be difficult with this chip. Also, is that a right half
plane zero I see lurking in this creation of yours???

Don't even say the P-word ("Phil" or "PIC", now that I think about it)!#$^&

 

[colin]

Well, my attempt to dismantle the transformer from a cheap-o CompUSA power
supply last night met with total disaster. The, one detail we both seem to
have forgotten is that commercial switchers tend to have their
transformers
dipped and/or vacuum impregnated. Needless to say, when I tried to
separate
the core halves I ended up breaking the ferrite into lots of little
pieces....
This does not bode well for re-winding the transformer on this beast:

http://www.weirdstuff.com/cgi-bin/category.cgi?item=22081

An otherwise excellent choice! Only $100 and you get yourself an honest
3kW
of 48V output. I'll probably buy one anyway and hope it uses a PQ44040
core
(as I have those in stock). The education one can glean just from taking
something like this apart is worth the price of admission!

Yeah if theyr glued or dipped or worse potted, then its hard,
sometimes soaking them in something realy disolving ie acetone
and sometimes the glue gives up if you get it hot enough,
but then that melts the plastic core wich is usefull to keep intact,
but I have used paper soaked with epoxy for a core on many occasion.

fortunatly the supply I had just had a clip holding it together,
no glue or varnish. ive glued broken cores back together before,
ofc this is only realy ok if its a gapped core anyway.
but ive got quite a few bits of broken cores lol.

but also I managed to get my full voltage out of the 5v winding by putting
in a much higher voltage switching transistor. you maye be able to use the
+12 and get quite a reasonable voltage out of it.

you can of course buy quite big ferrite core/transformers.

Colin =^.^=

 

[Adrian Tuddenham]

There are two banks of batteries in the pack, each containing 26 12V/42Ah
batteries. The manufacturer, Genesis, recommends charging them at the 0.4C
rate up to a maximum of 2.4V/cell (with -20mV/C of compensation). As this
comes out to a rather onerous 6.3kW, [...]

A linear and/or design using 60Hz magnetics is totally out of the question -
you won't be able to move the thing around without a forklift.

A pity. Some years ago I designed something similar using a motorised
Variac, with a current-sensing relay for control. It charged a large
bank of NiFe batteries.

The relay armature hovered between two contacts when the current was
correct. If the current fell or rose, the armature touched one of the
contacts, pulled-in an auxliary relay and drove the motor to wind the
Variac up or down by means of sprockets and a chain.

There was an interlock that ensured that the Variac always wound down to
zero before the battery circuit was closed. The main battery circuit
breaker was magneto-mechanical with a magnetic arc blow-out coil.

There was also a timing cam that pulsed a uniselector around at hourly
intervals until the voltage rose above a pre-set threshold value, then a
second uniselector was pulsed at half-hourly intervals until it caught
up with the first one and terminated the charge. That ensured that the
battery received the final third of its charge after it reached the
gassing point.

 

[Phil Allison]

"Adrian Tuddenham"

A pity. Some years ago I designed something similar using a motorised
Variac, with a current-sensing relay for control. It charged a large
bank of NiFe batteries.

** Whaaaaaaattt ????

Banks of large capacity Nickel Iron cells ?

Inside a Wehrmacht Tiger Tank maybe ??

Or a British Navy diesel submarine ?

Or the radio in a Ferret ?




........ Phil

 

[MooseFET]

I took a look at the LT part and agree it would be ideal for producing the
right gate drive signals, however, it is expecting to control a buck
regulator and the KenSmith idea certainly ain't one of those.

What the designers intended the chip for is just a limition of their
imaginations not ours. In fact, the KenSmith circuit sometimes looks
a little like a bucker. Right at the peak of the waveform, the
transistors aren't overlapping. It looks a little like a bucker
feeding a 2:1 step up squarewave.

Closing the
loop, then, might be difficult with this chip. Also, is that a right half
plane zero I see lurking in this creation of yours???

We are only charging a battery. The transient responce doesn't matter
too much. We can slow the circuit way down. There can be a very slow
soft start to ease it up to the regulated charging current and
voltage.

You really need a diode ORed control signal because you want the
charger to pour in the current right up to the charged state and then
back off to perhaps a holding voltage.

The pole in the RHP isn't lurking. It is jumping up and down, waving
and yelling. It has a couple of high frequency friends hidden out in
the weeds too.