battery charger harmonics

[drbond24]

I have three battery chargers that are used to recharge forklift batteries. I am looking for information on what sort of harmonics they (the chargers) might cause, but I am having no luck so far. Does anyone have any information on this topic? I have found a few vague references on the internet that suggest these chargers may severly distort the current, but I can't find anything concrete.

The chargers are Enersys Depth Chargers. Nameplate says input is AC 480V/14A and output is DC 36V/152A.

Any help is appreciated.

 

[wirenut1980]

Hmmm....I don't have any measured data on battery chargers. I would check with the manufacturer and see if they have harmonic spectra of the chargers. Any wiring diagrams on the rectifier?

On closer inspection, the load current is pretty small compared to your building load current and much much smaller than the available short circuit MVA, so even severe current distortion should not affect the voltage much.

 

[dereckbc]

Depends on the rectifier technology like switch mode, linear, or SCR control. If a problem should show up, doubtful it is easy to fix with a transformer.

 

[Lxnxjxhx]

And even a linear mode supply will have half-sine-like current pulses until the battery is fully charged.

 

[drbond24]

It is SCR.

I mostly just want to make sure they aren't messing with other stuff on the same panel. I was thinking of moving the chargers to a separate panel and putting an isolation transformer on the first panel to (hopefully) keep it normal.

 

[wirenut1980]

It is SCR.

I mostly just want to make sure they aren't messing with other stuff on the same panel. I was thinking of moving the chargers to a separate panel and putting an isolation transformer on the first panel to (hopefully) keep it normal.

This may or may not be necessary. You need to look at how much harmonic current distortion the charger will "cause." This is determined by finding out the harmonic spectra and THD of the charger and could be affected by the source impedance creating a resonant point. Then, find out how much voltage distortion the current distortion will create. The amount of voltage distortion is determined by the source impedance seen by the harmonic load, as well as how much of the total load at any point is actual harmonic load. Then see if the voltage distortion will have a negative effect on the other loads off the same panel and in the rest of the building by looking at what their respective distortion limits are.

The only way I know how to do this proactively is to use an expensive software program like ETAP or similar and model the system. An even easier way is to measure once everything is installed, but by then it could be too late.

Some other options besides what you have proposed is installing a simple line reactor, or better yet, a tuned filter on the line side of the charger, or maybe nothing needs to be done. With only 14 amps of harmonic load, I am guessing nothing needs to be done.