Voting Machine Charging and Storage

[Belgiovine Electric Inc]

Recently looked at a job for a county building in which the sub-basement is going to be used to house and store voting machines. They are estimating roughly 800 machines which when stored will be plugged in for charging purposes. The specs on the machines are fairly clear on how many machines can be daisy chained and how many can be connected to a single 20amp 120v circuit. As per the specs a 20amp circuit will support 10 machines which can be daisy chained in groups of up to 3. So I know I’d need at least 4 receptacles on each twenty amp circuit. My question is how would one calculate for feeder sizes of 2 or 3 new panels to provide the 80 necessary 20 amp circuit to feed these machines?


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[tortuga]

You basically need to do an article 220 load calc and figure out some kind of demand factor.
See 215.2, 220.40, 220.14(A) and 220.44
If each machiene has a 2A nameplate your receptacle load is 240VA per each.
240VA X 800 = 192000
Then 220.44 demand
First 10kva @ 100 %
rest @ 50% 91000 VA
total load 101000 VA

 

[Belgiovine Electric Inc]

That was my original thought. My worry was, what happens when all machines go out for election and come back and need to be plugged in and charged at the same time? Can, or or should I rather, really be able to apply those demand factors? Or maybe I’m over thinking it?


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[winnie]

I don't think you are overthinking that this _might_ be a problem. Demand factors are based on a certain randomness in usage, and here you have a situation where you might have simultaneous usage.

On the other hand, in a battery charging application the system probably runs at full blast for a period of time, and then dials back after the batteries are charged. If after an election these 800 machines get moved into storage and plugged in, it may be the case that the first ones plugged in are done before the last ones get plugged in.

My hunch is that the calculation tortuga did will be just fine. But it wouldn't hurt to call the company and get more info. They might have specific information for large warehousing situations.

Jon

 

[tortuga]

I agree with Jon, plus you could tell the county it will save x amount of dollars if say they only charge 400 at a time or something.

 

[petersonra]

My personal opinion is that you've added 1,600 amps of load at 120 volts.

Unless you can find some way to support the idea that few of the units will be drawing full load simultaneously. Even if you decided somehow that on average they're only going to draw 50% load, you're still looking at 800 amps of 120 volts.

I don't know what power you have available. If it is single phase 120 240 I think I would be inclined to install four 200 amp panels. That would give you the 1,600 amps.

It's a very good bet that you can get by with less, but I'm not sure how you would go about showing that in a load calculation. Or what you are going to do when they plug them all in at once and trip a main.

Depending on a type of charger, it may pull almost full load for most of the charging cycle. Other chargers start off at near full load when the batteries are all but discharged and taper off.

You are talking about some serious money here anyway. An extra panel board is not going to make that much difference cost-wise.

 

[petersonra]

One other thing you might want to consider. Some of these devices can suck an enormous amount of current for a couple of cycles when they start up. If you are fully loading the circuits, you might end up with a case where after a power failure ends, the startup current from the chargers might trip one or more circuit breakers. You're going to have to look at this and maybe talk to the manufacturers tech support people and see what they have to say about it. Better to know about it now than to find out about it after the next power failure.

 

[tortuga]

What about some kind of creative timer or load management set up?
Figure out the charging time say its 6 hours then cycle between say 100 outlets at a time

 

[Belgiovine Electric Inc]

Thabks to all who’ve replied, you input is greatly appreciated… So as per manufacturer each unit draws 1.4 amp while charging with a max of ten per circuit. So my original thinking was in order to be on the safest side I should account for that full draw for each machine, in the instance they are indeed all powered in the time frame they are at that 1.4 amp max draw, or as mentioned after a power outage which would be the only logical situation where all 800 could be powered up simultaneously. Maybe Tortuga is onto something with load management of some sort. As petersonra mentioned this is not going to be cheap anyway so maybe this would be something worth looking into.


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[jim dungar]

Ask the manufacturer for more information on the charging. in particular what is the float current and how they respond to a power cycle
I would not imagine you will draw 100% charging current for more than 3 hours, unless every machine was at 0% when they got plugged in at one time. At a rate of 4.44 machines per minute it would take 3 hours before they were all plugged in.

Ask the customer how they intend to use the plugs. I would think Tortuga's idea of some type of load sharing could be justified if the feed could be kept to 200A.

 

[synchro]

It appears that a least one voting machine manufacturer recommends periodic charging each month and having switched AC outlets. And so what tortuga mentioned about using a timer might be appropriate for such periodic charging, and it could also be used to cycle between different loads to reduce the peak power.

I think it would be appropriate to find out what the particular manufacturer recommends for charging, as well as getting info from the county about any specific needs they might have for charging.

 

[winnie]

Good point. I know that some computer systems complain if you leave them sitting on a charger continuously. IMHO this is a design flaw, but the OP is not here to discuss design flaws of the voting system, but to plug the system in.

In any case if the systems specifically require that they be unplugged periodically, then you might as well build the power system to take advantage of this.

Jon

 

[Belgiovine Electric Inc]

I will be contacting the manufacturer on Monday, and will update with new info after speaking to them thanks again to all that replied I truly do appreciate the community you have formed here… I will update with new info as it comes in. Thanks again.


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[Belgiovine Electric Inc]

So I wasn’t able to get much out of the manufacturer… Essentially they told me to figure for 1.4 amps per unit for the duration of the 2.5 hour charging cycle… that being said it seems powering them on and off in banks would be the best option… has anyone ever worked with any prebuilt equipment that would allow me to switch between banks of machines (or entire panels, I was think 4 or 5 200 amp panels) on a timed basis? Or is my only option to build this myself? I’m sure something exists, just wondering if anyone has any experience with a product they would recommend…


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[jim dungar]

Look at the panel boards used for energy management. Just about every manufacturer offers them. Contactors controlling entire panels used to be fairly common, but now they have breakers that can be controlled individually.

 

[zbang]

Unless the client is going to charge all 800 units at exactly the same time, and I find that highly unlikely, the actual demand and wiring is far smaller & easier. Even assuming they charge 100 a day, that's only 140 amps for under 3 hours (which could be 75 amps for 6 hours if they do two "shifts"), spread that across three phases and the problem becomes quite small.

From the original, it sounds like groups of 10 machines (3-4 receptacles) as a 14 amp * 3 hour load. Unless they want to pay for timers and automation, I'd look at groups of manually switched outlets*, and put 5+ groups of those on each 20a circuit; tell the client to only turn one or two on at a time or the breaker might pop (and let it, they'll learn). 80 sets of machines on (10) 20a circuits = 8 charging shifts, that could easily charge them all in a week.

*3-gang box with two duplex recep's and a switch, use standard parts

KISS and all that.

 

[Belgiovine Electric Inc]

I wish it were that simple unfortunately the machines go out all at once and come back the same way… they get plugged in and stay that way until the next election…. It like the old infomercial set it and forget it…


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[tortuga]

So I wasn’t able to get much out of the manufacturer… Essentially they told me to figure for 1.4 amps per unit for the duration of the 2.5 hour charging cycle… that being said it seems powering them on and off in banks would be the best option… has anyone ever worked with any prebuilt equipment that would allow me to switch between banks of machines (or entire panels, I was think 4 or 5 200 amp panels) on a timed basis?

Well its not a continuous load which is good news.
and if you have 3 phase 208/120 available you might be able to get away with four 125A panels controlled by large contactors so only one panel is on at a time. Using 4 wire MWBC you could load up each ckt to like 40 machines
Or as Jim suggested the energy management panelboards.

 

[zbang]

they get plugged in and stay that way until the next election…

It's all a matter of cost. If the customer really wants hands-off for many months, it'll cost them more. And you could do all the on/off with a row of time clocks or you could do it with "automation". There's also the question of switching loads on the branch circuits or switching feeders- I'm really in the "switched outlets" camp and using fewer panels and a smaller feeder.

An unanswered question- how much power is available at all? If you can only install a 150amp feeder, that helps drive the design.

 

[tortuga]

I'm really in the "switched outlets" camp

Yeah i agree, now that I think about it, you could use 3 pole contactors to control 4 wire MWBC and control 40 machines at a time.