Generator and ECM fan motors

[White Shadow]

I have a 22kw Generac stand-by generator. I also have two HVAC units that use ECM fan motors. My understanding is that ECM motors already somewhat "soft start" compared to traditional fan motors. However, I noticed the other day that my generator significantly dropped RPM when the A/C kicked on. One A/C unit was already running and when the second unit kicked on is when I noticed a big change in the generator's RPM. The generator also started surging, so I turned off the that second A/C unit, but the surging continued anyway.

So two questions:

1- Does it make sense to install a soft start on my A/C units even if I already have an ECM fan motor? Would the soft start help with the compressor? I'm thinking that's the big power draw that's causing the RPMs to drop during start-up.

2- Is there an issue with my generator since it continued surging even after I shut off one of the A/C units? When utility power was restored, I restarted the generator and it ran smoothly again. So I'm pretty sure the surging was due to the load at the time or at least the start-up load from the A/C unit.

 

[wyliesdiesels]

The fan motor on condenser units and the blower motor in the air handlers do not take much current at all. They are fractional horsepower motors. So your main concern would be the compressor

 

[dcg9381]

Generac builds "load shed" modules that need no wiring other the two hots (pass thru ground/neutral). They work by monitoring the frequency of the power on the hots. If frequency drops below 59 hz (we assume this is a drop in generator RPM), the load shed module disconnects the load and starts a timer. They also have "delayed start" so that any connected device won't go on at the same time as the main power.

 

[White Shadow]

Generac builds "load shed" modules that need no wiring other the two hots (pass thru ground/neutral). They work by monitoring the frequency of the power on the hots. If frequency drops below 59 hz (we assume this is a drop in generator RPM), the load shed module disconnects the load and starts a timer. They also have "delayed start" so that any connected device won't go on at the same time as the main power.

Hmm.....where are the load shed modules usually located? At the service panel? Maybe this is a better option than installing soft starts on the A/C units?

So if I understand you correctly, the load shed module would need to see a frequency drop before it disconnects the load? But wouldn't that mean that, in theory, my A/C unit might start (or try to start) before the load shed kicks in to shut it off? Or do I not understand? I guess what I'm asking is how that would help if it's not really allowing the unit to start using less amperage?

 

[dcg9381]

Mine are attached between the main panel and sub panels. I use a dedicated sub panel for our two "main" HAC units - all of this surface mounted outside, so it's easy to mess with.

The units do two things:

1) Delayed start when generator power comes back on. This has like 12 different "delay" settings. It allows the generator to get warmed up before energizing the circuit. If you have multiple devices to "shed" - you set the delays at different times. This way your generator comes on and it makes sure everything doesn't try to start at once.

2) It continuously checks power frequency. If it detects <=59 hz or less, it drops the load and resets it's "restart" timer. Yes, if you're over drawing power it will allow a re-start attempt.. It'll immediately shed and then wait another <timer interval - I think mine are 15 minutes> to try and restart that load.

No, it won't do anything to help your total draw. What it does do is prevent all the loads from hitting at once as soon as the generator starts. It also allows "priority" to some degree - All of the circuits behind the load shed are non-critical.

I have one "main" AC on a load shed device and I have our garage/garage apartment on another device. This means the house and at least one AC will always run off the generator.

 

[American Locomotive]

22kw is big and should be able to run multiple large AC units without issue.

If the engine is surging, you likely have a fuel flow issue. Either a dirty (or mis adjusted carb) or too small of a regular or supply line (if natural gas or propane)

 

[White Shadow]

22kw is big and should be able to run multiple large AC units without issue.

If the engine is surging, you likely have a fuel flow issue. Either a dirty (or mis adjusted carb) or too small of a regular or supply line (if natural gas or propane)

I thought about that too, but the surging isn't consistent. Like I mentioned, it started surging when the second A/C kicked on, but then it continued surging after I shut that unit off. And then when I restarted the generator, it wasn't surging at all, despite having the same overall electrical load on it.

I'm not really sure what's going on with it. I guess I can do my own testing by basically turning on everything in the house to see if it starts surging at all. The generator is about 6 years old now and has never given me a problem, but then again it only has like 85 hours on in in those 6 years, so it hasn't seen all that much use.

 

[dcg9381]

I'd clamp a load meter on it. I've got a 20KW unit, running 3 ACs (and goodness knows what else) - the most I've seen peak draw is 17kw. My generator is about the same age as yours (propane).

 

[wyliesdiesels]

fuel flow issues can be intermittent. id check that first

 

[theoldwizard1]

1- Does it make sense to install a soft start on my A/C units ...

Be aware that there are 2 different kinds of "soft starters". The cheap one are basically a large starting capacitor and will not help your generator. A good one will cost a couple hundred and actually limits the current for the first second or so (while the existing starting capacitor is charging). You get what you pay for !

 

[dcg9381]

Be aware that there are 2 different kinds of "soft starters". The cheap one are basically a large starting capacitor and will not help your generator. A good one will cost a couple hundred and actually limits the current for the first second or so (while the existing starting capacitor is charging). You get what you pay for !

Can you give more info? The RV industry has "soft start" capacitor kits sold all over the place that help many "marginally" powered generators. I'm running a 13.5K BTU HVAC with factory soft start on a 2500 watt onan...

 

[theoldwizard1]

Not sure how much "detail" you want ! Without getting into the technicalities of "how it works", one of the few companies sells a "true" "soft starter is" Micro-Air EasyStart.

It employs a 4-part start ramp sequence that is self-optimizing, resulting in the lowest possible start-up current. EasyStart can deliver a start current reduction of up to 75% of a compressor's LRA (locked-rotor amperage).​

I'm running a 13.5K BTU HVAC with factory soft start on a 2500 watt onan...

I am amazed it starts at all !

 

[White Shadow]

Be aware that there are 2 different kinds of "soft starters". The cheap one are basically a large starting capacitor and will not help your generator. A good one will cost a couple hundred and actually limits the current for the first second or so (while the existing starting capacitor is charging). You get what you pay for !

I'd most likely install one of these if I decide to go that route:

Hyper Engineering SS1B16-32SN V230 Hyper Sure Start Single Phase Soft Starter 230V 16-32 FLA

Buy Hyper Engineering SS1B16-32SN V230 Direct. Free Shipping. Check the Hyper Sure Start Single Phase Soft Starter 230V (16-32 FLA) ratings before checking out.

www.electricgeneratorsdirect.com

 

[theoldwizard1]

I'd most likely install one of these if I decide to go that route:

If it works as described, it should be good !

How It Works​

• Reduces locked rotor amperage (LRA)/inrush current up to 60% (Starting)
• Provides automatic optimization of motor start-up current

 

[White Shadow]

If ir works as described, it should be good !

How It Works​

• Reduces locked rotor amperage (LRA)/inrush current up to 60% (Starting)
• Provides automatic optimization of motor start-up current

Yeah, hopefully. These same units are also marketed as "Generac Soft Starters" and I've seen them under a couple of different brand names. I like that they are compact and from what I've seen, most guys are mounting them right inside above the contactor.

 

[American Locomotive]

I thought about that too, but the surging isn't consistent. Like I mentioned, it started surging when the second A/C kicked on, but then it continued surging after I shut that unit off. And then when I restarted the generator, it wasn't surging at all, despite having the same overall electrical load on it.

I'm not really sure what's going on with it. I guess I can do my own testing by basically turning on everything in the house to see if it starts surging at all. The generator is about 6 years old now and has never given me a problem, but then again it only has like 85 hours on in in those 6 years, so it hasn't seen all that much use.

Doesn't matter if its not constant, it should never happen. Your generator should be load tested and serviced to identify what's going on. The RPM of the generator should not noticeably change under load - especially with modern electronic governors.

 

[AP514]

OP ....FYI the Hyper Sure Start you have listed is for 16-32 AMP draw while already up and RUNNING...

Hyper Sure Start is a Great Choice I have it on my A/C unit..it cut my start AMPs down from 64 to 31.

Here is a link (post 1-2) https://www.garagejournal.com/forum/threads/hyper-surestart-soft-start.467347/

 

[White Shadow]

OP ....FYI the Hyper Sure Start you have listed is for 16-32 AMP draw while already up and RUNNING...

Hyper Sure Start is a Great Choice I have it on my A/C unit..it cut my start AMPs down from 64 to 31.

Here is a link (post 1-2) https://www.garagejournal.com/forum/threads/hyper-surestart-soft-start.467347/

Yeah, I didn't look at the specs to be honest. I just linked the first Hyper Sure Start I found with an image. I'll for sure have to make sure I choose the correct one though. Actually, two of them since I have two units.

 

[AP514]

Actually, two of them since I have two units.

It might actually be 4....if you have a High and a Low compressor on each unit.
My OLDER(Now 18-yrs) American Standard Allegaince 18's have 2 Scroll compressors on each unit.
I only purchased 2 EasyStarts to run my Smaller 2.5 ton unit.

 

[fitter30]

Ecm motors are a type of dc motor three phase. I'd call the manufacturer of the generator. They are variable speed and torque.

 

[nadogail]

When did ECM change it’s meaning from Electronic Counter Measures?