Forklift Battery Chargers failures due to brownouts?

[mjawhary]

I am running into a problem with a big warehouse facility where they have about 70 big battery chargers for forklifts. They are being fed from 2-3P-600A circuit breakers, some of those chargers get damaged where they have to replace the electronic board inside due to often electric brownouts and surges. Upgrading to better improved chargers could solve the problem but it is costly since the charger run about $3800, installing a large UPS unit is also costly for 2-3P-600A.
They are trying to solve the problem without having to spend quarter a million. Any suggestions?

 

[itsmoked]

Hard to say from here. Certainly something less drastic than replacement should be possible. Perhaps something that just disconnects or disables the controller board during an event. That way only a small load needs to be manipulated. That would require someone capable of looking at the control board and understanding it enough to retrofit a protection. Find an EE willing to look at it. Give him a few of the toasted boards. See what transpires.

Another question would be why there are brownouts. That's usually something that needs to be fixed anyway. That can cause havoc with refrigeration equipment.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[wayne440]

How old are the chargers? All the same age? Could simply be some component inside that reaches end of life, and nothing to do with power quality. Is there a common failure on the "electronic board inside"? If you can find out what particular component is failing, you may gain some insight into what to do about it.

Is the diagnosis "due to often electric brownouts and surges", proven by any physical evidence, or just a guess based on the fact the you have have experienced both brownouts and charger failures?

 

[rmw]

And, I suppose that all the chargers are put in service at about the same time too, further browning the brown out. I would assume that to be end of (day) shift at about the time that the grid voltage is suffering the most.

Can you put timers on the chargers to bring them on line (A) after the grid peak begins to subside, and (B) sequentially?

The forklift timer that I use at a warehouse that I own usually has the job done in just a few hours. It doesn't take the entire 15 hour period between the end of the day shift and the start of the next day so any time in between as long as enough time is allowed for a complete charge would work.

rmw

 

[electricuwe]

One quite common problem with DC-voltage link power electronics and brown outs is the following:

To precharge the DC-link capacitors when starting up the equipment there has to some kind of current limiting. This can be done by various means:

- NTC-resitor
- precharge resistor and relay
- precharge resistor and electronic switch
- half-controlled rectifier using thyristors

To operate properly in brown-out condition the following functions must be implemented:

- when the control detects brown out, further discharging of the DC-lin should be avoided, e.g. by disbaling pulses of the inverter stage
- When voltage comes back again, the precharge circuit has to be activated again

If the chargers are quite old and you do not have warranty on it (or you still have warranty, but dealing with brown-out is not covered in the applicable standard or specification), I'd recommend to hire someone to design and implement an upgrade for the missing functions (provided you have access at least to the schematics)

 

[ScottyUK]

Can you accept an interruption to the charger supply? An undervoltage release would proetct the charger, but would normally require intervention to reset it. With a bit more sophistication it would be possible to automate the reset too.

How frequent are the brown-outs?


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If we learn from our mistakes I'm getting a great education!

 

[sibeen]

A contactor fitted into the switchboard controlled by an undervoltage relay. Set the relay with a decent hysterisis so that the voltage is up at a decent level before re-closing.

As others have mentioned, it may be an idea to look at the cause of the brownout, as if it is the current draw of the chargers that is causing the problem you'll probably need some way to stagger the timing of the chargers coming on-line.

 

[PHovnanian]

First, have the charger manufacturer (or an outside engineer) take a look at the failed boards and determine the probable cause of the failures.

Some simple surge protection for the control boards might suffice for overvoltage events. If its undervoltage causing the damage, as others have suggested, perhaps adding undervoltage protection and/or staggering the charger start times could solve the problems.

If you add such protection, it would be wise to add some ON delay time in addition to hysteresis to avoid 'doorbelling' the chargers. With 70 units and the above protection functions, it might be worthwhile investigating a PLC solution to control everything. That'll give you some room to add additional protection, scheduling control and status monitoring.

 

[itsmoked]

Earth calling mjawhary. Are you getting any of this? Care to participate?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mjawhary]

Thank you all for the replies. I am installing a voltage monitoring device to report values over a month period, then I am thinking to consider hiring an electronics engineer to modify the circuitry inside the charger itself.

 

[potteryshard]

You might also want to look at third-harmonic current loading on the feeder neutral. The apparent brownout may be induced by paralleled chargers.

 

[itsmoked]

Good plan. Thanks for the come-back. We await your findings.

Keith Cress
kcress -

http://www.flaminsystems.com