Connecting a forklift charger

[bobsmate]

I've been asked to connect a forklift charger in a warehouse, so i rang up the supplier to find out what size rcbo to use and he told me to use a 50 amp, when i told him that the cable going into the charger was 4mm2 sy cable he told me it had been tampered with and that a 6mm2 sy cable should be used. I thought this was still a bit low and asked him if it had to be the higher temperature stuff but he said that and 6mm2 flex could be used. Does this sound right or should i upgrade it to 10mm2 sy cable?

 

[ColJack]

you've given us no details of the charger, it's input or anything so how would we know..?

for all we know the tech guy was wrong and it only requires 1.5mm 4 core..

 

[bobsmate]

Sorry, its a 48v 75amp, per 2 volt cell and is single phase.

 

[ColJack]

that's the cell rating? what about the charger input rating, the FLT itself is of no interest to us..

 

[bobsmate]

Right ok where would i find that out then? There's a 50 amp mcb inside the actual charger.

 

[ColJack]

there will be a plate on the charger giving you the electrical specs..

 

[RF Lighting]

Why are you installing an RCBO?

 

[ericmark]

From the information you give the charger will draw around 20A at 230V working on 2.45v per cell with 24 cells at 75A assuming no loses.

However the inrush on this type of charger often means a 50A type D MCB is required so it will not trip on switch on.

If my figures are correct then 4mm² would run the charger but would not comply with regulations as it is not what the charger uses that is important but what will protect the cable. As you seem to know 10mm² cable is rated at 51A for flex so it would require a 10mm² feed.

Because of the D Type it is likely even 10mm² will not comply with the earth loop impedance requirements and 16mm² will be needed to comply with BS7671:2008 requirements.

It is the time to trip that is the problem and using motor control overloads may allow you to use a lower overload setting and you may get away with 30A which would allow 4mm² cable. But at this you move into the area where only skilled persons are allowed to have access under Electricity at Work act. Since you are asking question I would assume you are not skilled.

So if you are checking up on the work of resident electrician then it may be acceptable to use 4mm² cable if he has used a fuse or motor overload at 30A. But if you want to do work yourself then you can't use less than 10mm². Even then I would say you are probably in breach of EAW act by doing any work on the system.

I do however see understand the problem as I was also caught out when a charger arrived with 32A plug and I was asked to provide a 32A socket. Which I supplied with a 32A D type MCB which tripped when the charger was switched on. And like you I contacted the supplier as I considered the charger to be faulty. I was also told it needed a 50A MCB which I refused to fit to a supply to 32A socket. The option I used was to supply with 32A fuses which would take inrush and because of ELI I also used a RCD in socket.

I will guess these chargers were designed in the days when we all used fuses and they are quite old.

Does that help?

 

[RF Lighting]

With a 50A type D, you'd be lucky enough to get a Ze low enough, before you start worrying about the Zs

 

[ericmark]

With a 50A type D, you'd be lucky enough to get a Ze low enough, before you start worrying about the Zs

Where I worked we had a 300A 3 phase supply and Ze was very low. But this was back in 2003 and memory is a little vague on exactly what we did. However I do remember the problem. The fork lift and charger were hired and this resulted in there being no way to alter the charger in any way. I wanted to use some form of soft start resistor which seemed favourite, but since not ours it could not be done. Also I was not permitted to change the plug and plug into a 63A supply as the supply cable on charger was not big enough. I was however able to move supply from MCB filled board to a Fuse board and I used a socket with built in RCD. We also ear marked for re-wire with 10mm SWA at latter date. We may have well used motor rated fuses but can't be sure on that.

It was only the inrush which caused the problem and once running it was OK. It was switched on and off but can't remember why many fork lift chargers are controlled by the connection of the battery and this may have been the case.

I think originally they would have used this

type of MCB which had no magnetic trip so would take the inrush but these are no longer used so a 50A D type MCB feed one of these

with 32A fuses even then some times the MCB would trip.

 

[toasty]

Don't these chargers have any inrush protection...?

I remember building a dirty great amplifier once which contained a pair of mahoosive toroidal transformers and using a special thermistor in series with them to limit the inrush current.

I can never remember if they are positive or negative temperature coefficient, but they are the ones that when cold have a high resisitance, and then warm up as a result of the current drawn, which causes their resistance to drop. This results in a nice gradual increase in current, rather than a big thump.

 

[ericmark]

Don't these chargers have any inrush protection...?

I remember building a dirty great amplifier once which contained a pair of mahoosive toroidal transformers and using a special thermistor in series with them to limit the inrush current.

I can never remember if they are positive or negative temperature coefficient, but they are the ones that when cold have a high resisitance, and then warm up as a result of the current drawn, which causes their resistance to drop. This results in a nice gradual increase in current, rather than a big thump.

The one I worked with did not. Had it belonged to us I would have modified it but it was hired so I had no such option.