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amps on back-to-back setup

 
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bunt1828




Joined: 13 Sep 2016
Posts: 5



PostLink    Posted: Fri Feb 16, 2018 4:30 am    Post subject: amps on back-to-back setup Reply with quote


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For those using the 50A back-to-back panel, what amperage do you usually max out at?

I'm aware the theoretical max with two 5500W elements is 45.8A, but I'm guessing that most folks wouldn't begin heating the 2nd batch until the 1st has reached a boil and the boil PID has been reduced to ~75%. Is that the case? I'm not required to follow the 80% rule, but think it's probably a pretty good idea anyway - does anyone regularly exceed 40A with two 5500W elements? If I reduced both PIDs to 85% when running both kettles does that mean I'll be at 39A?

Thanks
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kal
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Joined: 12 Dec 2010
Posts: 11116
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Fri Feb 16, 2018 5:14 am    Post subject: Re: amps on back-to-back setup Reply with quote

bunt1828 wrote:
I'm aware the theoretical max with two 5500W elements is 45.8A

Not true. You're assuming that the mains voltage is fixed at 240V but it may actually be higher (or lower) and the power, and therefore current draw will also vary.

Regional power companies try to adhere to a range, usually. Often governed by nationally defined standards. I'll use my area as an example. I'm in Ottawa Ontario Canada and am powered by Ottawa hydro.

The standards they attempt to adhere to are here in table on page 7: https://static.hydroottawa.com/documents/specifications/ECG0008.pdf

Summary:

Nominal Voltage (RMS V): 120 / 240V
Allowable Deviation from Nominal (%): +4.17% ; -8.33%
Normal Minimum Voltage (RMS V): 110V / 220V
Normal Maximum Voltage (RMS V) : 125V / 250V
Reference : At Service Entrance per CSA CAN3-C235-83 Table 3.0

So your 120V nominal can vary from 110-125V and 240V can vary from 220-250V.

But there's no guarantee really. If you read it carefully there are some weasily words:

HOL ( Hydro Ottawa Limited ) will endeavor to maintain the voltage in the distribution system in accordance to CSA document CAN3-C235-83 in steady-state (i.e. periods of time longer than 3 seconds) and will endeavor to follow the Information Technology Council (ITI / CBEMA) voltage tolerance envelope limits (see Appendix A: ITI (CBEMA) Curve Application Notes) for short-duration (i.e. periods of time 3 seconds or less) voltage variations. Customers may, on occasion, experience voltage variations outside these limits (see Table 2 and Table 3 of this document).

There's also mention of extreme conditions (i.e. really hot days in the summer when AC's are running everywhere):

Nominal Voltage (RMS V): 120 / 240V
Allowable Deviation from Nominal (%): +5.83% ; -11.67%
Normal Minimum Voltage (RMS V): 106V / 212V
Normal Maximum Voltage (RMS V) : 127V / 254V
Reference : At Service Entrance per CSA CAN3-C235-83 Table 3.0

Long story short, the high voltage limit they try to adhere to in my area is 250V.

The heating element rated power (watts) are when they are run at the normal 240 volts. You can run them with more or less, but the current and power changes. The heating elements have a fixed resistance:

5500W = 10.47 ohms
4500W = 12.8 ohms

And we know that:

Current (I) = Voltage (V) / Resistance (R)
Power (P) = Voltage (V) * Current (I)

So at the normal 240V a 5500W element has a current draw of 22.92 amps and the power is 5500 watts
Lower the voltage to 230V and a 5500W element has a current draw of 21.97 amps and the power is 5053 watts
Increase the voltage to 250V a 5500W element has a current draw of 23.88 amps and the power is 5970 Watts

So the theoretical max isn't 45.8A with 11000W wort of elements running. There is no theoretical max as the voltage can vary. Increase to 250V and it jumps to 47.8A

So that said I'm not really answering your question. Wink

Most will say ignore the 80% loading rule. I would agree. I only mention it as it's code, but the code is vague in this situation. So I can't in good conscious tell people that "they'll be fine". I want them to ask/confirm for themselves. That said I've yet to hear of anyone being told to adhere to the 80% rule on a brewing setup.

Cheers!

Kal

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bunt1828




Joined: 13 Sep 2016
Posts: 5



PostLink    Posted: Fri Feb 16, 2018 7:42 pm    Post subject: Reply with quote

Thanks for that detail and the quick response. You're right - I hadn't considered the mains would vary, but that makes a lot of sense. I suppose I should have changed "theoretical max" to "theoretical value".

I guess I also do not understand exactly how PIDs work. If you set it to run a 5500W element with 240V supply at 75%, does that mean you'll see a "steady" 17.2A? Or does it quickly oscillate between 22.9A and 17.2A (or 11.5A or 0A) as the element is fired on and off?


I'm still interested in hearing from anyone who has used this setup - what amperage does your control panel read when running both elements? I guess if nothing else your response helpd me feel comfortable starting with two 5500s. If I run them and feel uncomfortable, I can always swap one out for 4500 later.. Thanks!
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kal
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Joined: 12 Dec 2010
Posts: 11116
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Fri Feb 16, 2018 8:09 pm    Post subject: Reply with quote

Take a look here at how PIDs work:

http://www.theelectricbrewery.com/control-panel-part-2?page=11

The element is either on 100% or completely off. Cycle time is typically 2 seconds, so setting a PID to 75% power means that the element will be on at 100% power for 1.5 seconds, then at 0% power (off) for 0.5 seconds. This then repeats.

bunt1828 wrote:
I'm still interested in hearing from anyone who has used this setup - what amperage does your control panel read when running both elements?

That depends on their mains power. Your mains power will not be identical to theirs. Assuming that they have the nominal 240V shown on their voltmeter and that the voltage doesn't sag (lower) at all under load (unlikely) the amp meter would show:

Current = Power / Voltage = 11,000 watts / 240 volts = 45.8 amps

In practice for most people this will likely be a bit lower, but that's not guaranteed. I guess what I'm trying to say is that it doesn't matter what others see as that isn't what you'll see. Wink

You can certainly run our back to back (50a) control panel with two 5500W elements. In our FAQ I simply mention that the 80% rule exists as the rule's a bit of a grey area. The 80% rule is about the wiring in your walls - it has nothing to do with the quality of our control panels which are perfectly fine to run at 50A. It's an electrical code rule that talks about how much you can load wires in your walls. I simply mention the 80% rule for full disclosure so that people are aware of it, for liability reasons. Most people completely ignore the rule.

If you're interested in running 5500W elements, I'd just go with that.

Cheers!

Kal

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Master




Joined: 30 Jan 2016
Posts: 171
Location: Virginia Beach, VA

Drinking: Naked Singularity Stout, Hurricane Bohemian Pilsner, Pineapple Cider, Ich bin ein Berlinerweiss, AbbyNormal Glutton Free Lambic

Working on: Vienna Lager. Witty name to follow.


PostLink    Posted: Sat Feb 17, 2018 10:36 pm    Post subject: Reply with quote

I'm running 5500's on my Back to Back setup.

Full load, both pumps on, both elements firing manual 100%, I see about 47 amps full bore. Pumps don't draw much. Panel draws something like .2 amps to run.
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kal
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Joined: 12 Dec 2010
Posts: 11116
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Sun Feb 18, 2018 2:07 pm    Post subject: Reply with quote

Sounds about right! My pumps draw about 1-2 amps when both are running.

Kal

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canofworms




Joined: 18 Nov 2017
Posts: 4
Location: SoCal


PostLink    Posted: Sun Feb 18, 2018 9:26 pm    Post subject: Reply with quote

When calculating the current draw of an element for those of us without amp meters....

Current (I) = Voltage (V) / Resistance (R)

The Voltage should be the mains voltage without the element actually running correct? So basically panel at idle right?
As there is obviously a small voltage drop when I have 2 element running.

Just making sure I'm not crazy...
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kal
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Joined: 12 Dec 2010
Posts: 11116
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Sun Feb 18, 2018 10:40 pm    Post subject: Reply with quote

canofworms wrote:
The Voltage should be the mains voltage without the element actually running correct? So basically panel at idle right?

Correct.

FYI - Resistance of the 5500W elements is fixed at about 10.4 ohms, while resistance of the 4500W elements is fixed at about 12.8 ohms.

Quote:
As there is obviously a small voltage drop when I have 2 element running.

Yup. That's normal.

Quote:
Just making sure I'm not crazy...

That I can't confirm. Wink

Kal

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canofworms




Joined: 18 Nov 2017
Posts: 4
Location: SoCal


PostLink    Posted: Sun Feb 18, 2018 11:26 pm    Post subject: Reply with quote

Thanks Kal for confirm 2 out of 3.... crazy is expected in home brewers right ?? Very Happy
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kal
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Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Sun Feb 18, 2018 11:31 pm    Post subject: Reply with quote

A little bit of crazy is always good! Thumbs Up

Kal

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ParadiseBrew




Joined: 09 Dec 2014
Posts: 83
Location: paradise, ca


PostLink    Posted: Tue Feb 27, 2018 11:00 pm    Post subject: Reply with quote

on my panel, i pull 46.3 with two 5500W and two chugger pumps.... Mine is off of 50amps and I have had no issues!!
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itsnotrequired




Joined: 15 Sep 2015
Posts: 177
Location: central wi


PostLink    Posted: Wed Feb 28, 2018 2:38 pm    Post subject: Reply with quote

that '80% rule' is an nec item that relates to continuous loads. basically, overcurrent protection and subsequently the circuit conductor needs to be sized at 125% of the rated load for continuous operation (125% is the reciprocal of 80%, so limiting a continuous load to 80% of the protection device rating or sizing the protection device at 125% the rating of the load means the same thing). key phrase here is 'continuous'. nec defines a continuous load as 'a load where the maximum current is expected to continue for 3 hours or more'. most folks take 'continuous' to mean just that; a sustained, 100% on load for three hours. a cycling load like that controlled by a pid is an on-off load so does not meet the requirement of continuous, at least in my (and most professional's) opinion. of course, it can be treated as continuous if you want to be conservative. after all, is there really any practical difference between a load that runs for six hours straight verses one that runs the same amount of time but shuts off for one second at the 3 hour mark?

but in homebrewing, is anyone really reaching the three hour limit for continuous? even with a two hour boil, looking at maybe 2.5 hours total time counting ramp up to the boil. hlt is a similar time frame, maybe 45 minute heat up so could mash for 2 hours and still not hit three hours.
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kal
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Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Wed Feb 28, 2018 2:49 pm    Post subject: Reply with quote

itsnotrequired wrote:
but in homebrewing, is anyone really reaching the three hour limit for continuous?

Exactly. You'd have to do a 3 hour boil (including ramp up) without any cycling. I.e. The PID running at 100%. That would be incredibly rare. I've only come close one: A 2 hour boil for a high gravity barleywine I was trying to reduce. Heating to boil took about 30 mins, so 2.5 hours total, but I didn't run the element 100% once at boil (only 85%).

Now that said you did forget one caveat to the 80%/125% NEC rule: It states also that "A fixed storage-type water heater that has a capacity of 120 gal or less shall be considered a continuous load". In other words, any water heater has to follow the 80%/125% rule even if the element isn't firing for 3 or more hours straight.

So the brewer arguments made for and against going above 80% load typically revolve around whether someone thinks that the elements will be fired for more than 3 hours continuously (as you mentioned - something pretty rare) and/or whether or not an electric brewing setup is classified as a "fixed storage-type water heater" (given that we use electric heating elements pretty much identical to ones found in hot water tanks and the functionality is somewhat similar).

I frankly don't think it's an issue and haven't heard of any commercial brewer being told to adhere to the 80% rule, but because the rules exist and they're not entirely clear how a brewing setup fits in, I simply point it out as a discussion point people should have with their electrician.

Kal

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Last edited by kal on Fri Mar 02, 2018 7:03 pm; edited 1 time in total
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itsnotrequired




Joined: 15 Sep 2015
Posts: 177
Location: central wi


PostLink    Posted: Wed Feb 28, 2018 5:39 pm    Post subject: Reply with quote

true, there are a couple exceptions about certain loads that are treated as continuous no matter how they are operated but they don't apply to electric brewing setups. even the storage-type water heater requirements don't apply. yes, the elements are similar but the requirement is for fixed water heaters, meaning those that are hard-piped, not readily moveable, hard-wired, etc. unless you bolt the brew kettle down or hard-plumb it or something like that, i don't see how the argument could be made it is a fixed storage-type water heater.

if anyone has doubts or concerns, by all means, apply the 80% rule. it isn't a violation to go above code minimums. just recognize there may be additional costs for larger circuit breakers, larger conductors, etc.
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kal
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Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Wed Feb 28, 2018 9:52 pm    Post subject: Reply with quote

You make a valid point about "fixed" vs "not fixed". Frankly, I'm thinking I should just remove all mention of this NEC rule as it's caused more confusion than it warrants in most cases.

Cheers!

Kal

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itsnotrequired




Joined: 15 Sep 2015
Posts: 177
Location: central wi


PostLink    Posted: Thu Mar 01, 2018 1:40 pm    Post subject: Reply with quote

it really does cause confusion. folks have heard 'something' about the nec and continuous loads but don't have the complete story, specifically the three hour time requirement. or their 'electrical buddy' tells them to never exceed 80% of the breaker rating. it is just bad information but fortunately, the worst that comes out of it is breakers/conductors get oversized. typically not a problem other than increased costs. Very Happy
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kal
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Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Thu Mar 01, 2018 2:51 pm    Post subject: Reply with quote

Agreed. I've now removed that 80% NEC rule text.

Kal

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hobbes




Joined: 08 Sep 2017
Posts: 26



PostLink    Posted: Sat Aug 25, 2018 10:28 pm    Post subject: Reply with quote

bunt1828 wrote:
Thanks for that detail and the quick response. You're right - I hadn't considered the mains would vary, but that makes a lot of sense. I suppose I should have changed "theoretical max" to "theoretical value".

I guess I also do not understand exactly how PIDs work. If you set it to run a 5500W element with 240V supply at 75%, does that mean you'll see a "steady" 17.2A? Or does it quickly oscillate between 22.9A and 17.2A (or 11.5A or 0A) as the element is fired on and off?


I'm still interested in hearing from anyone who has used this setup - what amperage does your control panel read when running both elements? I guess if nothing else your response helpd me feel comfortable starting with two 5500s. If I run them and feel uncomfortable, I can always swap one out for 4500 later.. Thanks!


The pids will toggle the element "on" a percentage of the cycle time... if you watch the amp draw you will see it go to full bore for a bit, then drop down like theyre "off" and toggle back on.

If your running back to back then at a particular time you may show none, one, or two elements worth of draw depending on what your doing.
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