Are there typical demand factors on battery chargers in an industrial facility ?

[bdn2004]

We've got a line-up of forklift battery chargers fed from a 600A, 480V panelboard. The total connected load on the panel is 608 amps. The Plant wants to install some garage door openers on the spare breakers in that panel. Without connecting power monitors and recorders is there a scientific answer to that could justify the additional load? Like a typical demand factor for multiple battery chargers in an industrial facility?

 

[waross]

Go into the accounting office and ask for copies of the power bills for the last one or two years.
Find the highest monthly demand and compare that with the service size. If you have unused capacity, you may increase the load on the service.
Another option is to use an Automatic Transfer switch wired so that when a door is operated, the power to a battery charger is interrupted and the door operator is powered by the battery charger breaker.
Or, you may "roll your own" by using a pair of interlocked contactors.
And if the battery chargers have internal contactors, you may do it all with control circuits.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[itsmoked]

Whoa.. we're talking garage door openers! Those are n o t h i n g compared to 600A of chargers. Maybe a 1/4A?? Not to mention they run for what, almost 10 seconds at a time once or twice a day? I'd not worry about them.

Those chargers also look fancy enough to allow setting the maximum charge rate. The longer the period of charge time is the longer the batteries will last. I suspect you could add hours to the charge times without affecting fork lift usage and extending the battery life. Perhaps you can drop that 608A down to 500A or less.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Hi Keith. With that bank of chargers I am thinking BIG doors, and maybe a lot of them.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[bdn2004]

These are big garage doors. Semi trucks back into them. The fork trucks unload the semis. There's another load to be added which is a natural gas air curtain heater with an electric blower that blows when the garage door is opened we are told. These would be more of a continuous load and the bigger load. Someone said air curtains are only on when the door is open and no truck sitting there. We think the garage door is 1 Hp, and the blowers on the fans max 2 hp. And they want to add three doors. So close to 10 Hp of new load.

 

[waross]

Do an assessment of times of use.
While a door is opening or closing for a truck, is the forklift nearby or is the forklift on charge?
When calculating demands on panels, and two loads will not be use at the same time, the load may be calculated on only the largest of the two loads.
The textbook example is electric heat and air conditioning.
If you are able to show that the doors will not be used at a time when all of the battery charger load is in use, a reasonable AHJ will accept the plan as code compliant.
Do you have dock levelling ramps as well? (Maybe 1/2 HP, short time duty.)

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[bdn2004]

Yes the door and the leveler are one control box and electrical connection. This is at a factory. During the 8-hour shift those forklifts are in constant use. Then they put them on the charger. My question is ... A battery that's been fully charged vs a battery that has just gotten 8-hours of use and is then put on the charger. How much current is the battery charger pulling on the feeders in each case?

 

[waross]

The input current will be roughly the same ratio sa the output current.
Full output current will require full input current.
10% output current will require approximately 10% input current.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!