Difficult battery charger task

Dear All, I have been given a task to design a battery charger for SAFT batteries in series. There are 170 batteries in series. The charge current is 12Amps.(6A above a level) The discharge current is 120 Amps. I have never dealt with high currents before. The charge voltage is 170

*2.1 = 357 volts. I consider to use LM350's in parallel to limit the charge current but will they withstand such a high voltage? Any suggestions for the circuit? And how am I going to limit the discharge current to 120A? Any Ideas? Thanks
Reply to
boothmultipler
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My favorite related movie quote: "You're gonna need a bigger boat."

What he's doing sounds identical to the charging part of a 3-phase UPS, and these can be found for junkyard prices if you look in the right place.

Tim.

Reply to
Tim Shoppa

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Either let us design it for you or post an address where we can send
the flowers.
Reply to
John Fields

Here's some more fodder for the pros' hilarity... I can see why they emit Bronx cheers in this case. But what the hell:

view in proportional font

load about .005 ohms 100 watts _____/\\/\\/\\________ _____________/\\/\\/\\_____________ | _|___|_ _|_ | | | _ / \\ | | | |_______/ V____________| | | | | | / | | \\ | | / | |_____________________\\ | | ground __|__ _ _____ _ _____ _ | | ground

You will need a farm of parallel mosfets or a honkin igbt.

Reply to
kell

Are you really serious?

Reply to
Tom Biasi

Why do I have the impression you're in the wrong movie ? You should get yourself a battery driven screwdriver and buckets full of semiconductors. For each incidential short you're going to change a plate full of them. You attempt to build a series regulator ? A switcher is better suited for these power levels. The load has to get rid of 40kW ? That is quite a bit of water running ... Not to meantion that DC from an impedance that low is able to supply sparks of 5cm, once ignited.

Rene

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Reply to
Rene Tschaggelar

You never did say which battery chemistry you are using.

Best regards mark

snipped-for-privacy@hotmail.com wrote:

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Mark W. Lund, PhD            ** Battery Chargers
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Reply to
Mark W. Lund, PhD

LOL!

I was eating spaghetti thinking, "Oh God, please let him not fire up that circuit without a friend around..."

Luckily, I had large paper towel handy. :))

-Chaud Lapin-

Reply to
Le Chaud Lapin

He'll probably be cremated..

martin

Reply to
martin griffith

Sounds like your manager needs to learn how to match the task to the skill/experience level of the asignee. Your question indicates that you're not the right person for this task. Farm it out. mike

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Reply to
mike

Wait with the flowers till the batteries are exhausted then ...

Rene

Reply to
Rene Tschaggelar

I don't know how to solve your problem. But I can tell from your question that I am 10x closer to solving it than you are.

I strongly suggest that you tell your boss you simply CANNOT do this, or else budget in enough time and money for you to study up on it by reading real serious text books that specifically deal with high-voltage, high-power DC supplies.

Applications engineers may be able to help you, too, but they only have so much patience unless you are planning on making a lot of these things.

Debugging a circuit like this can be dangerous, and very challenging, since you might not even be able to hook up your oscilloscope directly to it. And if you accidentally connect the oscilloscope ground probe to the wrong part of your circuit you might experience a bright blue arc and even have to shop for a new oscilloscope.

The original post included SED twice, as well as sci.electronics.basics, and sci.electrochem.batteries or something like that. I dropped everything except SED.

--Mac

Reply to
Mac

OK Boyz, You have fun, at least tell me how to do this safely. How will I limit the current without being electrocuted.

Reply to
boothmultipler

The chemistry is Silver -Zinc.

Reply to
boothmultipler

Some comments:

2.1 volts per cell will not charge a lead-acid battery cell fully. You may have intended a nominal 1.2 volts for nickel cadmium. Big difference.

A properly rated fuse will limit the output to 120 amps, but actively limiting the current is difficult. The wrong (non-DC rated) fuse may just burn with an internal arc on DC. Use heavy duty 600vdc disconnect switches.

Consider modifying a variable speed dc motor controller to charge the battery if a noisy waveform is acceptable. These are available in the power levels you need, but the voltage may be a problem.

Variable speed AC motor drives often have a DC buss voltage of about 400 volts and a feedback loop to control the voltage.

This is serious voltage and power, be careful and get help before you get into trouble. Look for a company that sells/repairs industrial dc equipment. I understand that ships use a lot of high voltage dc, might be some help there. Also, look into larger UPS systems. Bill Kaszeta Photovoltaic Resources Int'l Tempe Arizona USA snipped-for-privacy@pvri-removethis.biz

Reply to
Bill Kaszeta / Photovoltaic Re

This is the first time I've seen a charger spec'd to limit the battery's discharge current. Are you sure you've got that part right? Bucking 120A at 400V could be a serious challenge. Perhaps paralleling multiphase circuits or partitioning the load might be a good idea, if possible.

As to charging, the simplest configuration could be non-isolated PFC boost circuit(s), operating off of a stiff n-phase lower line voltage, if there's no-one there to work the magic with hefty LF magnetics.

You haven't stated the input source requirement, or whether isolation has been ignorantly specified, as well.

SAFT develops chargers as a loss-leader for their battery sales unit. You might contact them to see what they have to offer, already in the can.

RL

Reply to
legg

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Get someone else to do it.  I\'m not kidding.  At your level of
expertise, no matter how excellent the help you get here, you will
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Reply to
John Fields

This may or may not apply to your situation.. but it may give you ideas...

I build a high voltage DC source by putting a number of small Lead Acid gell cells together in series... about 600 volts worth I think...

I did it this way.... I brought all the batteries out to a home made connector that consisted of multi pin strip connectors stacked side by side... all posts got a pin in the connector. My charging connector mated to this and I charged the thing as a parallel 12V cell. I got my High voltage by making a connector that tapped off it in series. It was always scarey plugging that connector in But we didn't kill anyone...

We were messing with electrostatic underwater transducers if anyone wonders why..

No idea as to how to limit your current...

Al...

Reply to
Alan Adrian

What does "6A above a level" mean?

What discharge current is that? The max load on the batteries while you are charging?

If you have to ask about the LM350's then you are totally unqualified for the job.

Yeah- get someone else to do it, you obviously have no knowledge or interest in electronics or circuits.

Reply to
Fred Bloggs

To do it safely. Remain 5m or more away from the apparatus under power, or with the batteries charged at all times. Cover the battery with a cover adequate to catch any shrapnel. If you need to look at things closer, use a video camera/webcam.

Run the leads of the batteries (divided into 30V or so groups) outside the cover.

Connect several adequately rated knife switches mechanically together, and use these to isolate the batteries, so they are at a safe potential. Make sure you can visually see that all the knife switches are disconnected before approaching. NEVER go anywhere near the battery pack with any metal buttons/tools/ eyeglasses/rings. Wire the groups of cells up seperately, and case them seperately.

Reply to
Ian Stirling

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