Starting 5ton HP off generator

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Old 07-21-16, 09:57 AM
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Starting 5ton HP off generator

It may be electrical question but I'll try here.

I have 5 ton Trane HP.

I have 2 x 200amp 220 panels in the garage.
HP has furnace set on one of the panels. Furnace has 3 x 60amp breakers.
Furnace has ELECTRIC auxiliary heat.
Three heating elements.

I found last winter that furnace will not start off my generator. I am presuming, t-stat is run off DC current from furnace.
With inside temperature way below t-stat preset and gen running full power, furnace showed no signs of turning on. NONE. As in - none.

Generator is 8 000 running and 11 000 max. I had entire 2500 sf house running off it, furnace and all, at the old place but furnace there was natural gas.

I had an HVAC guy yesterday, he finished installing mini split system in ADU..

He told me that because HP is electric, it requires huge electric current to start and will NOT kick off this generator. His opinion was unless going into industrial type generators, nothing residential will actually work..

Is this correct? Practically, then I am hosed for winter outages.
 
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Old 07-21-16, 12:54 PM
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My gas furnace starts and runs fine off a 3'000 watt generator without straining. I'm not sure why your's wouldn't work on one much larger. I'm assuming something else was going on since you mention that your furnace did absolutely nothing. It may not have been on one of the transferred circuits.

To figure if your existing 8/11kw generator will work with the new heat pump you/we need to know it's power requirements. Also does it have gas or electric for backup/emergency heat? I can run my main AC off my 11kw generator but it's at it's limit starting.
 
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Old 07-21-16, 01:11 PM
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running the mini split will be easy with a portable generator. so you should easily have good heat and AC. the electric furnace is going to need a lot of power to run the heaters. With out working it up id guess 16k. You should have been able to power 1 circuit with 8k
 
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Old 07-21-16, 01:34 PM
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Oyy...

It's ELECTRIC heat pump with three auxiliary electric heat elements. That was guy's reasoning: because those three elements require so much power to start, it won't kick in off generator.

I am only making sure that his theory is plausible - not enough power supply to electric heat pump with three heating elements causing no start.
 
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Old 07-21-16, 05:56 PM
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Even small heat strips can pull 5 or 10k so they alone would strain or kill your generator. I would look at the current draw of your heat pump without auxiliary to see if running it will be an option for you.
 
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Old 07-21-16, 07:19 PM
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Thread moved to electrical.
 
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Old 07-21-16, 09:13 PM
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The only label I could find on Trane says what voltage is required. nothing about power draw.
I'm just trying to figure out if it can or can not be started off generator.
If it can and does not, then there is something else going.
Reason I keep asking this is simple. I know how gen behaves when loaded. It "crouches" so to speak, then takes laod and goes back to normal work. When I had it connected this winter, there was NO, I mean - NO signs of any extensive load on possibly coming from furnace.
That's what keeps bugging me. Like furnace completely ignored generator power supply. Didn't even try.
 
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Old 07-21-16, 09:26 PM
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The inside heat strips will NEVER run off your generator. Your looking at about 48 amps, or 11,520 watts per heater. That is not going to work.

Your air handler should work just fine off your generator IF it has it own 120 volt feed. The control wiring between the heat pump and air handler will be 24volts AC not DC (Unless it is something new and fancy)

The outside heat pump should have a nameplate on it listing the amps, max overcurrent, and min circuit ampacity. If it doesn't then you will need to remove some panels and find a model number.
 
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Old 07-21-16, 09:35 PM
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You would need to have your heat pump modified to run in heat pump mode only when on generator. It wouldn't be that hard. You'd need to lockout the electric reheat coils.

Usually if the house is warm and you transfer over to a generator the reheats wouldn't come on.
They're basically setup to come on when the actual temperature is 3 degrees below the setpoint.
 
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Old 07-22-16, 06:23 AM
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If everything else works OK on the panel that is connected to generator it is possible that the power from your generator is not "clean" enough.
Some electronics do not do well with a standard generator which could be your problem.
The controls on your furnace should at least try to bring on the HP so it can then at least stall the genny if it is too small.

Generator is on a transfer switch right?.......and it is wired correctly?
 
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Old 07-22-16, 06:26 AM
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What circuits in your house are powered by your generator? I am betting/guessing your transfer box does not include the furnace/heat pump since your old unit did absolutely nothing.

Your heat pump probably is on three circuits. One 120v 15 or 20 amp for the air handler inside the house. A 240v circuit for the outside compressor and another 240v circuit for your emergency heat strips.
 
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Old 07-22-16, 09:00 AM
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There are three 60A 240vac circuits for the heatstrips. I'm guessing one of those three circuits is also the blower and controller power.
 
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Old 07-22-16, 11:09 AM
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Thank you guys.
I know what to do.
Damn, wish I had my 'ol electricians back. It's so hard to find decent priced and work one.
 
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Old 07-22-16, 11:12 AM
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Also, thing is, it does not start in electrical heat. It's heat pump. It turns auxiliary strips on only if it can not pull enough heat from the outside. Winters are rather warm around here, I saw it run aux heat strips only once. I do not believe it is requiring all that huge power to simply run the blower and electronics and fan outside in exchange unit.
 
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Old 07-22-16, 04:49 PM
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Exchange unit? Condenser ? There is a compressor outside. That may draw 15-20A at 240v.
 
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Old 07-23-16, 10:15 PM
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My HVAC guy had his meter today on heating strips power supply wires.
All 3 strips that actually do engage the first thing furnace turns on, pull 19.8 Kw.
My gen is 8K running 11K peak. There is no way.
Also, heat pump is on subpanel and furnace is on main panel. Guy told me they should be connected in parallel and still kick in, but not without enough power.
We also found another problem - short in t-stat control wires to furnace. As the result, furnace starts on 3 aux heating elements, but then shuts 2 down or all 3, and runs on heat pump only. What produces very lukewarm air and HP runs non stop. When all 3 aux heat strips were engaged, we had 161 degree coming out of vents. Can't hold hand against it.
He'll be back September to either find that short or replace entire wiring from t-stat to furnace. Took him 2 hrs today to investigate.
 
 

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