Difficult battery charger task

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

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

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

Are you really serious?

You never did say which battery chemistry you are using.

Best regards mark

snipped-for-privacy@hotmail.com wrote:

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-

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

The chemistry is Silver -Zinc.

Some comments:

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

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

--- 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 certainly make an error somewhere along the way and put yourself, someone else, or the equipment in danger.

---

--- Limit it to zero by staying away from it.

-- John Fields Professional Circuit Designer

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...

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.

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.

You're right. We decided to use a High Voltage Battery Charger from PowerDesigners (PowerCharge HV Series). For the Discharge, the Batteries have to be discharged before Charging. I still don't know how to limit the discharge current at 120A.

The OP can't do the project as he described it safely. He just doesn't know what he's doing.

But since he's going to try it anyway, Mr Stirling gave some very good advice. The OP should carefully follow all the precautions and good advice in Mr. Stirling's list.

If I could, I would add at least a pair of real polycarbonate safety goggles which are ANSI Z87.1 compliant, and a pair of rubber insulating gloves. He should go to an electrical supply house for these rather than buy the cheapie imports from the "do-it-yourself-poorly" mega hardware store down the street. For the most part, the megastores sell wannabe toys, manufacturing culls and QC rejects for safety equipment.

A good pair of goggles and insulating gloves will reduce the chance of eye damage or electrical burns, but only if they're used.

Chris

Much better. All you need now is a 3 ohm, 43,200 watt resistor bank. That's not as difficult or as expensive as it might seem (although it will cost quite a bit)..

Try calling Surplus Sales of Nebraska. They've got tons of wirewound power resistors, and will help you design the least expensive load bank for your application. Remember to use the correct mounting hardware, manufacture a frame with sufficient air space between resistors to avoid hotboxing, and remember generous use of forced air (the 20" box fans they sell for $15.00 USD each at the hardware store are really good for this).

Use a remote voltmeter to determine the correct point to disconnect the load bank, and you're good to go.

Mr. Stirling's advice is still valid for switching and releasing the load bank. And please remember the rubber gloves and safety goggles.

Good luck Chris

Yes they do. Bodies smelling of charring are particularly offensive to the olfactory system ;-)

...Jim Thompson

Much better. All you need now is a 3 ohm, 43,200 watt resistor bank. That's not as difficult or as expensive as it might seem (although it will cost quite a bit)..

Maybe a bank of water heater elements, it will make enough hot water for several showers; nice to go to the hospital clean, the morgue doesn't care though. Tom

| > 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. | | The OP can't do the project as he described it safely. He just doesn't | know what he's doing. | | But since he's going to try it anyway, Mr Stirling gave some very good | advice. The OP should carefully follow all the precautions and good | advice in Mr. Stirling's list. | | If I could, I would add at least a pair of real polycarbonate safety | goggles which are ANSI Z87.1 compliant, and a pair of rubber insulating | gloves. He should go to an electrical supply house for these rather | than buy the cheapie imports from the "do-it-yourself-poorly" mega | hardware store down the street. For the most part, the megastores sell | wannabe toys, manufacturing culls and QC rejects for safety equipment. | | A good pair of goggles and insulating gloves will reduce the chance of | eye damage or electrical burns, but only if they're used. | | Chris |

Ditto to the above and would add a buddy system. All parties should have first aid with CPR. Never work on this kind of device alone.

Don't forget the eye wash station and neutralization solutions for spills ...

Is hydrogen buildup going to be a problem?

Fire fighting systems? Structure? Are you going to locate your battery room behind the washroom? Floor loads? Fusible links in the heating, ventilation and air conditioning plenums. Is this thing going to be safe?

Add a couple dozen more items in a 24-7 backup system for replacement of defective cells.

The OP is clearly over his head. It might be to his credit to walk away rather than bungle the job.

BTW anybody know how to limit the discharge current to 120 Amps ;)

Dan