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How does a forklift battery charger works?

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Kal_B

Member
Good day gentlemen,

We have a few of those battery chargers and I'm curious as to why the drivers must press the stop button on the charger before unplugging the battery form it.
I understand that if the charge is complete then they can unplug it without pressing stop as it would have already stopped but if they want to unplug it before the charge is complete then they must press stop first. What happens electrically that necessitate that?


Thanks
Kal
 

alec_t

Well-Known Member
Most Helpful Member
If you open a switch carrying a large DC charging current there will be an arc generated across the switch contacts, which can burn/erode the contacts and cause a lot of electromagnetic interference.
 

JimB

Super Moderator
Most Helpful Member
If you open a switch carrying a large DC charging current there will be an arc generated across the switch contacts
Agreed.
It is also worth noting that there is a big difference between a DC arc and an AC arc.

The AC arc is to an extent "self extinguishing". Because the current goes to zero every half cycle, the arc will soon stop as there is no current to ionise air molecules.
A DC arc however will just keep on going until the airgap gets too big. Unless you can break the connection very quickly it can get quite exciting.:eek:

JimB
 

Les Jones

Well-Known Member
Most Helpful Member
The spark / arc could also trigger an explosion by igniting the hydrogen / oxygen gas that may have been produced during the charging.

Les.
 

Cicero

Active Member
If you open a switch carrying a large DC charging current there will be an arc generated across the switch contacts, which can burn/erode the contacts and cause a lot of electromagnetic interference.
Just gonna add to this, although it may seem obvious, that when charging the batteries from flat the current will be very large (and have arcing potential), and as the battery gains charge slowly (and hence voltage level rises) the current will decrease slowly to a very low level (negligible arcing potential). So the arcing potential is large at the beginning and gradually decreases slowly in proportion to the current.
 

Mickster

Well-Known Member
Most Helpful Member
Also, contacts which have been subject to damage from arcing can also present a higher resistance and generate more heat.
 

Kal_B

Member
Thanks everyone. So what I can see the charges does when I press the stop button is a contactor is de-energized cutting off the main 600VAC supply to the circuit, is that all that is necessary to protect the contacts?

Thanks
Kal
 

MikeMl

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Thanks everyone. So what I can see the charges does when I press the stop button is a contactor is de-energized cutting off the main 600VAC supply to the circuit, is that all that is necessary to protect the contacts?
Since the charger has rectifiers in it, then current never flows backwards from the batteries to the charger. If you remove primary power, then there will be zero current in the charging cable as it is unplugged.
 

dr pepper

Well-Known Member
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Amongst other things I maintain Flt's, unfortunately most drivers dont use the cancel button on the charger, they dont have time, surprisingly there hasnt been an explosion yet.
Some of the better makes put a link in the andersen connector, so that when you start to unplug the charger it has chance to cut off before you interrupt the charge current.
 
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