Problems with surge current

You can certainly use a surge protector on mains-driven devices. It won't give you what you want.

In order to sustain devices through a power black-out you need an UPS [uninterruptible power supply], which is basically a mains rectifier, a battery charger, a load of batteries and an inverter, all controlled by a packet of useful electronics.

Carlos57, do you use "snubber circuits" to suppress voltage spikes?

(Diodes, Mov's, RC circuits, in parallel with output device)

James

no, some machines are very old and still use S5 PLC.

The spike on the low-voltage is a lot less than on the incoming primary voltage.

If your boards operate at 5 volts and your incoming voltage is 120V, a twenty volt spike would only be less than one volt on the 5 volts to the board.

You might have another problem.

Undervoltage can be harder on electronics than overvoltages due to they way most circuits are designed. The excess voltage can be shunted somewhere.

Also, a one volt spike is huge to a CPU or memory. A UPS is the way to go. You just have to size it correctly. If the the power "cuts" are long, you may have to invest in a generator as well. A good UPS will condition the line voltage as well.

Hello AccuDave,

I agree with you, an UPS is the way to go. I have one which gives about 50 minutes after a blackout, to get organised and save all files etc.

As far as I know there is no 'stand alone' UPS which will give much more than an hour. But, as you say the UPS could be linked in-line with a Generator.

I did have a pretty expensive surge protector but, a spike blew all but one socket which is when I got the UPS.

jfmfit

You could consider including a voltage stabilizer, isolation transformer and surge suppressor(tvss), while taking the UPS option, for optimal power quality, reliability and availability. It all depends on how sensitive (or vital) the load is and how much you have for spend.

would also check size of neutral cables are not too small or loose neutrals as can contribute to abnormal circulating currents. Good luck.

By the way AccuDave,

that's a picture of my uncle...............or is it aunt?

jfmfit

You may have impulses coming from any coil or motor in your facility. Place Mov's on any coil or motor around. Put them on the motor leads and coil leads. This will suppress any impulse spikes at the source.

You may need to use them on every input and output, but you need to make sure the range of the Mov is good for the voltage used.

A resistor/capacitor snubber can also be used, but they are limited in effectiveness. A 220 ohm resistor with a .47 mf cap (make sure it is 600 volts or better) is less expensive.

These techniques may be in some of the units you have already, so check the manufacturers documentation if available.

If you can get ferrite cores and wind the line inputs thru them several turns you will get even more protection.

Look in to your grounding on all the electrical equipment as this can help limit some types of problems of this nature. Study "Ground Loops" to see if this could be part of the problem.

Try to run separate runs for power as far back to the power source as possible. Don't go overboard, but the length helps slow the high frequency pulses due to impedance.

Sometimes a voltage regulating transformer will help. Use Mov's on the incoming and outgoing sides.

Good luck!