MEP 803a Short Circuit / Air Conditioner startup.

[devilphrog]

I called my HVAC company about the soft start kits and warranty as my HVAC units are both a year old, they are such a new / unique item in the residential world that they had no idea as to what I was talking about in regards to this equipment and hadn't installed any in a residential project. I may have to send them the data sheet.

I think it's a DIY project to install, but I'm concerned about losing warranty coverage if I add a soft starter. I do want to install one to be able to run both units in my house.

 

[impi]

So I went ahead and jumped in with both feet and got a soft start kit from MicroAir.net I bought the 368 unit which is rated for up to 6ton units. The results are quite drastic. The startup peak amps went from 121 Amps with the hard start kit, to a peak of 32 Amps when the compressor fires up with the soft start kit settling down at around 17 Amps running. Will test the MEP startup ability and let you know how it goes.

I know this is most commonly used for an RV but I don't see why you can't put one on your AC at home. I've seen videos of these in action and they appear to make a HUGE difference. Soft starts are very common on industrial equipment. They are becoming much less so with the gain in installations with VFDs on motor loads. Looks like the cost is reasonable for what you could get in return. According to the sheet you can start a 6 ton unit on 38 amps. That would bring it into range that a 803 can handle. Might be worth a conversation with the vendor.

http://microair.net/main/products/specsheets/EasyStart_Spec_Sheet.pdf

 

[Guyfang]

One of you rocket scientists explain how this soft start kit works. First off, almost no house here in Germany has air con, so its something I just haven't installed but 4-5 times in the last 25 years. Second, no one has back up power, or better said, only the farmers. When we do install a building for air con, its mostly factory's, big shops or very large warehouses. Then we use a star/delta switch, to soften the draw. So instead of me dying stupid, someone explain this soft start stuff to me.

 

[impi]

The short version is - a hard start gives it a voltage kick to spin up the compressor quicker, a soft start is more of a gradual ramp. Cost wise a hard start kit is a lot cheaper ($80 vs $380).

Here's a good writeup.

http://www.gen-pro.biz/faq

One of you rocket scientists explain how this soft start kit works. First off, almost no house here in Germany has air con, so its something I just haven't installed but 4-5 times in the last 25 years. Second, no one has back up power, or better said, only the farmers. When we do install a building for air con, its mostly factory's, big shops or very large warehouses. Then we use a star/delta switch, to soften the draw. So instead of me dying stupid, someone explain this soft start stuff to me.

 

[devilphrog]

Effectively, it's a a current limiter that 'slowly' ramps up compressors and motors in a stepped fashion to operating speed instead of throwing full amperage at once.

It applies like 30 amps, waits for inrush current to drop off, then another 30 amps a few milliseconds later, wait for current to drop back, than another 30 amps a few milliseconds later until at 100% speed rather than 120 amps all at once to go from 0-100% all at once

 

[jaxbill]

So I went ahead and jumped in with both feet and got a soft start kit from MicroAir.net I bought the 368 unit which is rated for up to 6ton units. The results are quite drastic. The startup peak amps went from 121 Amps with the hard start kit, to a peak of 32 Amps when the compressor fires up with the soft start kit settling down at around 17 Amps running. Will test the MEP startup ability and let you know how it goes.

I've been talking to them but haven't pulled the trigger yet. What size unit is this? Is it a heat pump or air conditioning unit?

 

[Guyfang]

Thank you!

We use a Stern/dreieck switch. When you push the start button, the Star configuration starts the air con and then the start switch, (after a short pre-determined time would automatically reconfigure itself into Delta configuration.

 

[Guyfang]

Effectively, it's a a current limiter that 'slowly' ramps up compressors and motors in a stepped fashion to operating speed instead of throwing full amperage at once.

It applies like 30 amps, waits for inrush current to drop off, then another 30 amps a few milliseconds later, wait for current to drop back, than another 30 amps a few milliseconds later until at 100% speed rather than 120 amps all at once to go from 0-100% all at once

Sounds like my Star Delta switch.

 

[impi]

This is a 5 Ton AC unit. The LRA on it is 141 Amps. With hard start kit it drew 121. I bought the EasyStart 368 which covers 4 to 6 ton AC units.

I've been talking to them but haven't pulled the trigger yet. What size unit is this? Is it a heat pump or air conditioning unit?

 

[devilphrog]

Did you leave the hard start kit installed when you installed the soft starter?

 

[impi]

No, the hard start kit comes out based on their instructions - regardless if it's factory or aftermarket. I just crimped female spade connectors on the soft start unit's wires and it pretty much just clipped in place. The run wire was the only one that had to be but spliced onto the soft start unit.

It took me longer to examine the wiring diagram and verify that I understood their instructions than the time it took to do the actual installation. I'm a bit paranoid about letting the magic white smoke out of electrical components - they're never the same after the smoke leaves.

The soft start unit is pretty big - fortunately I had room where I could mount it to.

Did you leave the hard start kit installed when you installed the soft starter?

 

[jaxbill]

The startup peak amps went from 121 Amps with the hard start kit, to a peak of 32 Amps when the compressor fires up with the soft start kit settling down at around 17 Amps running.

What is that model of the meter are you using?

I have a lower-end Fluke which doesn't have an "inrush" function. I have to watch the screen to see the spike. Then I bought a $25 clamp on meter with a "maximum" function. It only shows the peak but I imagine it's not the best sampling rate for this price.

I mention this because my 3.5 ton heat pump with a LRA rating of 112 was showing only 30-40 A surge. After I installed the OEM hard start kit it reads as if it's only 14 A. I have a pair of CTs that also suggest the surge is around 14 A but again no idea on the sampling rate. These numbers don't even seem realistic.

Do I need a more expensive meter with an inrush feature?

 

[impi]

It's a Tacklife CM04 - overpriced pos from Amazon. Blinded by the True RMS labeling - failed to see the lack of Min/Max etc. Documentation severely lacking as well. I overpaid for what it does. I just video it with my phone and then scroll through the footage to grab the frames showing the spike. I realize that this is will most likely be frowned upon by those in the industry - but it gets me near enough.

What is that model of the meter are you using?

I have a lower-end Fluke which doesn't have an "inrush" function. I have to watch the screen to see the spike. Then I bought a $25 clamp on meter with a "maximum" function. It only shows the peak but I imagine it's not the best sampling rate for this price.

I mention this because my 3.5 ton heat pump with a LRA rating of 112 was showing only 30-40 A surge. After I installed the OEM hard start kit it reads as if it's only 14 A. I have a pair of CTs that also suggest the surge is around 14 A but again no idea on the sampling rate. These numbers don't even seem realistic.

Do I need a more expensive meter with an inrush feature?

 

[jaxbill]

Ok - good to hear you're not using a $400 meter. I need to go back to the drawing board to figure out why I'm getting such low readings. Glad your kit is working for you. Hopefully your MEP can start it now.

 

[impi]

Video of 5 ton AC starting with soft start and adding 2 ton ac.

Glad to report the soft start does a great job. The attached link shows the startup. The MEP 803 is running with no load - no circuits on the panel are on other than the two air handler units and the two AC compressor units. The video shows the compressor fan coming on and the amps going up to 8 amps on the 5 ton unit. This is then followed shortly after by the compressor kicking in peaking around thirty something and then dropping back and settling around 19 amps. Once this is settled I add a 2 ton AC unit to the mix. The 2 ton does not have a soft start kit installed, but I suspect it does have a hard start installed, the LRA on it is given as 54 and I only see a jump of around 40 amps when it kicks in. Once it's started up and settles down the two units combined pulls around 24 amps. Considering that this is with only the AC's running I might consider installing a similar unit on the 2 ton. Will do a bit more detailed analysis later to see how it behaves once all critical circuits are on and if the well pump kicks in as well. Hope this helps.

Regards

https://youtu.be/97EMG6xA_kk

 

[DieselAddict]

The Fluke 87 I use has a special "fast" mode for this kind of stuff. You have to hold a key down while you turn it on to enable it. Otherwise its sampling rate is too low to catch this kind of thing. If you see sample rates in specs you need something with a capture time of a couple of milliseconds max. If not you won't catch the real peak.

 

[DieselAddict]

Glad to report the soft start does a great job.

Outstanding!! Glad its working.

 

[jaxbill]

That is excellent. I am sold. With only a single 3.5 ton heat pump at my house, this should more than enough for me. Since you're in Florida, does that same unit also provide heat for you? or do you a have a totally separate heating system?

Edit - can you also tell us the source for those cool meters you have installed?

 

[impi]

I have electric heat which sits in the same air handlers and makes for a very convenient load bank for the MEP. With both switched on the combined draw on each branch sits at just over 7600 w, and just over 63 amps so great for load testing (Family is less impressed when I switch the heat on but fortunately doesn't have to happen often).

The meters were sourced of Amazon.

I give a detailed breakdown in the following post.

https://www.steelsoldiers.com/showt...e-smoke-out)&p=2126599&viewfull=1#post2126599

 

[jaxbill]

That's great for a load bank. And I forgot you already told me your outside unit is AC only and not a heat pump/AC combo. I keep forgetting the farther south in Florida you go, you don't see as many heat pumps because they're just not needed.