Help with hooking up a variable speed air handler to a generator

[kybaseball]

Hope somebody can help me out. I purchased a generator as a back up when the electric goes out. I have a trane variable speed air handler and trying out to hook this up. I have purchased a Protran transfer switch that hooks to the generator. I have my owb and other things we need to get by figured out. Any help would be appericated.

 

[deutzman]

Hope somebody can help me out. I purchased a generator as a back up when the electric goes out. I have a trane variable speed air handler and trying out to hook this up. I have purchased a Protran transfer switch that hooks to the generator. I have my owb and other things we need to get by figured out. Any help would be appericated.

What's your concern with the variable speed unit and generator? I've never worked with that type of product but do work heavy industrial electrical. Where I work we run some AB vfd's on a generator if we have a power failure. It's all 3 phase 480 vac. These units have to run after power failure to insure the dryer drums cool down while turning to prevent warping of the drums. I read on another forum about the same as your posting about but never saw an explanation as to what the problem could be. Figured I'd ask since I'm not registered on the other site. I may learn something.

 

[krushing73]

My generator runs my variable speed units. Not sure why that makes anything more complicated. The main question is do you have enough KW to start the outside compressor. Or power heating coils ( depending on season ). Do you have an auto transfer switch or do you plan to transfer manually?


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[kybaseball]

I have a 7500 watt generator that I will be using. I plan in putting in a 10 circuit transfer switch. My bother in law thought the generator wouldn't be enough to run the air handler.

 

[krushing73]

I have a 7500 watt generator that I will be using. I plan in putting in a 10 circuit transfer switch. My bother in law thought the generator wouldn't be enough to run the air handler.

It probably won't start the outside compressor on your AC. That is probably what he meant.

 

[krushing73]

http://www.briggsandstratton.com/us/en/generators/home-generator-systems/buying-guide

A great site for sizing generators.

 

[OH_Varmntr]

I have a 7500 watt generator that I will be using. I plan in putting in a 10 circuit transfer switch. My bother in law thought the generator wouldn't be enough to run the air handler.

If we are indeed talking about running the air handler, we need more information.

Can you list what you plan on running off of the generator, and what each items' electrical load is? I have a feeling that you may be overloading the inrush capabilites of the generator when you try to start the air handler after other circuits are already loading the generator down. That could be what your BIL was thinking, and he could be right.

What are the exact specs of the 7500-watt generator you are referring to?

 

[UpOnTheHill]

Load test your 2 hot legs feeding your breaker panel while everything is running that you want to run on the genset. This will tell you if you have enough capacity. Get or borrow a clamp-on meter or a "fork" meter for measuring the load (amperage). The Abb drives previously mentioned have no relation to what you are trying to accomplish. I would make a "wish-list" of everything you think you want to run on the genset/transfer switch. Add up the load by either looking at all the nameplate data or doing a load test. If you don't have enough capacity with the genny, start eliminating things from the list until you are under. I'm always careful on what I run on my portable generator. I don't use expensive electronics while on genny power, but some do. Mine doesn't have any filtering or suppression so the power is not the cleanest.

 

[deutzman]

kybaseball wrote "I have a 7500 watt generator that I will be using. I plan in putting in a 10 circuit transfer switch. My bother in law thought the generator wouldn't be enough to run the air handler."

I just installed 8500 watt / 10,000 watt for my son a few days before Christmas. He wanted to try the heat pump with nothing else running and it wouldn't start. Tripped the breaker on the generator. He also has an oil furnace and it uses the same fan as the heat pump for the duct work and it ran that with no problem and hot water heater and well all on at the same time but started at different times. This spring we will try the air conditioner from the heat pump but will delay the fan from starting till the air conditioner is fully started and then start the fan. I think that will work. Just need to get each motor running one at a time before starting another and be reasonable with how much you can run at the same time. Only other option is to buy a larger generator. He's happy with what he has if we can get the air conditioning working and if that works out the heat pump may run as well with the delay for the fan. I'll use a timer to start the fan.

Your first post about the variable fan had me thinking why a generator wouldn't work because input power would be the same. I see no reason for any problem there. The Allen-Bradley VFD's don't care where the input power comes from as long as it's the proper voltage.

I have a PTO generator 13,000 watt running and supply my whole house but I have no heat pump or hot water heater. I use a plate exchanger from the Central Boiler for hot water. My blower for heat is 3/4 hp, have refrigerator, chest freezer, washer/dryer and electric range and small microwave. I use led lights all over the house, 2 computers and 2 Tv's. Generator has no problem pulling it all or any combination without a grunt from the tractor. On the tractor I shift to 1000 rpm pto and run the 540 rpm pto generator. Engine runs at 1,200 rpm instead of 2,100 rpm on 540. Engine is 96 hp and has fuel management and only burns what is required for the load. Burns about a gall per hour. Can run 38 hours on a 40 gal. fuel tank. I don't let the tank go empty and always refuel at 38 hours or before.

To test the generator while in use I use a Fkuke meter to check voltage and HZ and a hand held amp clamp for amps. The generator is brushless and is regulated. But I still check each time I use it to be on the safe side.

I don't use a transfer switch but use a mechanical interlock on the breaker panel. Less expensive and simple to operate.

 

[UpOnTheHill]

kybaseball wrote "I have a 7500 watt generator that I will be using. I plan in putting in a 10 circuit transfer switch. My bother in law thought the generator wouldn't be enough to run the air handler."

I just installed 8500 watt / 10,000 watt for my son a few days before Christmas. He wanted to try the heat pump with nothing else running and it wouldn't start. Tripped the breaker on the generator. He also has an oil furnace and it uses the same fan as the heat pump for the duct work and it ran that with no problem and hot water heater and well all on at the same time but started at different times. This spring we will try the air conditioner from the heat pump but will delay the fan from starting till the air conditioner is fully started and then start the fan. I think that will work. Just need to get each motor running one at a time before starting another and be reasonable with how much you can run at the same time. Only other option is to buy a larger generator. He's happy with what he has if we can get the air conditioning working and if that works out the heat pump may run as well with the delay for the fan. I'll use a timer to start the fan.

There should already be a delay between the indoor fan and the heat pump compressor. The indoor fan should always start first, then the pressure switch should make - proving airflow, then your compressor should be allowed to run. I would not recommend starting the compressor first, you would have to jump out the pressure switch. The airflow proving device is there so you don't freeze the evaporator coil like a block of ice (seen it happen a few times). I'm really surprised the compressor wouldn't start with that size genny. The startup amperage must be too great, I'm sure the RLA (run load amps) is within range unless its a huge heat pump. What gauge wire is installed between the genny and the transfer switch and from the transfer switch and the outdoor unit? Also what is the generator rated for in output amps and what is the FLA (full load amps) of the outdoor unit. I'm sure you sized it right, right?

 

[hedge hog]

I have a 7500 watt generator that I will be using. I plan in putting in a 10 circuit transfer switch. My bother in law thought the generator wouldn't be enough to run the air handler

your generator is 31.25 amp what is your breaker size for the for the air handler what going to be the total of breakers in your transfer switch box? what the distance ?

 

[UpOnTheHill]

your generator is 31.25 amp what is your breaker size for the for the air handler what going to be the total of breakers in your transfer switch box? what the distance ?

Breaker size and actual load are 2 different things. The wire should be sized to the load, no more than 80% of the wire rated maximum current and the breaker should be sized to the wire maximum current. Example - 10awg wire is rated for a maximum of 30 amps, therefore a 30 amp breaker is required but it can be wired to any load requiring 24 amps or less. My genny can produce 20amps at 240vac so I use 10awg wire. He should be using 8awg which is good for a 50 amps maximum (40 amp maximum load). The extra 20% is a safety factor for startup current. Wire length affects the load also - the longer the wire, the more the voltage drops, therefore increasing the current required for the connected load. This usually doesn't come in to play much in a house unless the genny is far away from the house or the connected load is far away (an outbuilding far away from house).

 

[kybaseball]

I want to keep the generator in a building that is 100 feet away from my house. A lot of good ideas from you guys. I think the interlock system is a better way to go.

 

[deutzman]

There should already be a delay between the indoor fan and the heat pump compressor. The indoor fan should always start first, then the pressure switch should make - proving airflow, then your compressor should be allowed to run. I would not recommend starting the compressor first, you would have to jump out the pressure switch. The airflow proving device is there so you don't freeze the evaporator coil like a block of ice (seen it happen a few times). I'm really surprised the compressor wouldn't start with that size genny. The startup amperage must be too great, I'm sure the RLA (run load amps) is within range unless its a huge heat pump. What gauge wire is installed between the genny and the transfer switch and from the transfer switch and the outdoor unit? Also what is the generator rated for in output amps and what is the FLA (full load amps) of the outdoor unit. I'm sure you sized it right, right?

Generator has a 30 amp plug. Used #6 wire and it's about 15 ft. long. Heat pump/blower running pulls 11 amps. Start up it pulls 39 amps. Thanks for the info on the compressor and fan. I didn't know anything about them. A friend where I work had the same problem in the summer when the direito came through and lost power. His blower is on a separate breaker from the heat pump/ air conditioner. He would turn the breaker off on the blower and start the air conditioner and when the generator motor smooth out he'd switch the fan on. He did that for several days and had no problems. His was 8500/10,000 watt also.

 

[kybaseball]

I get a daily reading of how much electric that I use and it usually is 55kw or below. Don't know if this helps with the size of the generator.

 

[deutzman]

I want to keep the generator in a building that is 100 feet away from my house. A lot of good ideas from you guys. I think the interlock system is a better way to go.

I talked to the folks I get my power from and said it was OK to use this. The last one I bought had a nfpa sticker on it also. They are pretty simple to install. Have to move a breaker or 2 to another slot and install the new breaker on the upper right side of the panel and then drill several holes and tighten up the screws and it's done. First one I bought was $149. The last one I got from a company in NJ that wasn't online when I bought the first one and got it for $57. Anyone can operate it and is safe.

 

[UpOnTheHill]

I get a daily reading of how much electric that I use and it usually is 55kw or below. Don't know if this helps with the size of the generator.

You are probably using 55kwh, not 55kw. Kw is how much electricity you are using at a given moment. Kwh is how much you are using over time. Two different things really. I really doubt you are using 55kw at a house unless you have a house and farm all running off the same service. It's definitely possible, but not typical for a house. If you are using 55kw, a 10kw generator ain't gonna cut it, not even close.

 

[UpOnTheHill]

Unless you just run a few things off of it of course.

 

[hedge hog]

Breaker size and actual load are 2 different things. The wire should be sized to the load, no more than 80% of the wire rated maximum current and the breaker should be sized to the wire maximum current. Example - 10awg wire is rated for a maximum of 30 amps, therefore a 30 amp breaker is required but it can be wired to any load requiring 24 amps or less. My genny can produce 20amps at 240vac so I use 10awg wire. He should be using 8awg which is good for a 50 amps maximum (40 amp maximum load). The extra 20% is a safety factor for startup current. Wire length affects the load also - the longer the wire, the more the voltage drops, therefore increasing the current required for the connected load. This usually doesn't come in to play much in a house unless the genny is far away from the house or the connected load is far away (an outbuilding far away from house).

yes I know all of that but what I was getting at he only has 31 amps of power.