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  1. #1
    Join Date
    Jul 2012
    Posts
    7

    Hard start kit vs. bigger generator.

    In Maryland, we've been having an increasing number of blackouts due to bad weather. We already had a small 3500/4400w (continuous/peak) generator hooked into a 10 circuit transfer switch. When we installed that system, we decided not to consider powering the central air conditioner.

    Then a major heat wave combined with a REALLY bad weather, resulted in 100+ degree weather, half the state being blacked out for up to a week, and our decision to upgrade the generator to power the whole house hvac system.

    We're running a single phase (~240v) Trane XE1200 with a rating of 12 RLA and 65 LRA. Not realizing the importance of the AC unit's LRA value. We bought the biggest generator we could find sitting on a shelf at Lowes, a Generac Xg8000e 8000/10000w unit. Upgraded the generator side electrical wiring in the house from 10 gauge to 6 gauge. Fed the new wiring into a dedicated sub panel and piggy backed our orignal transfer switch panel off of the new subpanel. We put in a 20 amp dual pole circuit breaker into the new sub panel and feed that into a 30 amp, center-off Leviton 1288 a/off/b dual pole switch, to cleanly switch the ac between line power and generator power, the furnace blower motor was already wired into the original transfer switch panel.

    So, after upgrading the generator, supply wiring and power distribution... The ac wouldn't turn over. That's when we realized 65x240= 15600, we were at least 5600 watts short of the power needed to start up the AC, 12x240 = 2880 but we had more than enough power to sustain it, once it was started. We were prepared to exchange our Generac for the larger Gp175000e (17,500/26250w) unit...

    Then we read about Hard Start kits and their ability to deliver serious, yet brief jolts of current to an ac unit for easier startup. We ordered a Supco Ssp8e Electronic Potential Relay hard start kit. When I opened up the ac there seemed to be a hard start cap 5-2-1 style already there. Installed the supco in parallel with the existing start cap, across the herm and common connection of the main dual purpose cap.... No luck, still wouldn't start up under generator power.

    Then, I removed the old starter cap and just left the supco unit installed, across the herm and common connectors of their dual purpose cap and... Bingo(!) Ac started up and has been running properly all day. On a day when it's 105 degrees out side, we're at 76 degrees inside the house, under generator power. The temp did climb to 79 degrees while I did the hard start kit install but dropped back down within an hour or two.

    So what am I missing here? What's the down side of using a 30 dollar hard start kit (capacitor ) vs. paying an additional 1500 dollars to get a 17500w generator? At the very least, I'll probably want to keep a spear Hard Start kit handy. But is there a downside to this setup?

  2. #2
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    The old start kit may have been bad.
    If more government is the answer, then it's a really stupid question.

  3. #3
    Join Date
    Jul 2012
    Posts
    7
    I did check the plug on the old cap. It looked intact but, I guess the relay could have been crappy.

  4. #4
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,665
    Call a Trane dealer and have them come and install a trane start kit get the original equipment kit it will be way more than the supco but also way better

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,069
    Old start kit was bad.
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    How many times must one fix something before it is fixed?

  6. #6
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    My experience is that a true hard start kit, with potential relay and start capacitor is better than any of the 'mini' hard starts. There is a real hard start kit available for your compressor and it will perform flawlessly for many years. The 'mini' hard starts tend to be useless when they're hot, just when you need them the most. JMO.
    If YOU want change, YOU have to first change.

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  7. #7
    Join Date
    Jul 2012
    Posts
    7
    For me the confusion is setting in, in terms of what works and what doesn't in a generator powered situation. I think what you guys are saying is that old cap and relay that was in the system was probably long since dead. Therefore my AC unit was really drawing those 65 amps on startup. And, given that the compressor is still within spec, until I hooked it up to an undersized generator that doesn't drive 65 amps... I wouldn't have known the old startup cap was bad.

    Now that i've put in a new albeit, generic start cap, I'm seeing the difference cause for sure the startup amps aren't coming from the generator, but being dumped back into the compresssor by the cap.

    The question is, is there anything special about the generic cap aside from the fact that it's 187 - 227uF and has it's own timer? Verses the original cap that was 133 - 167uF and controlled via relay connected to the contactor?

    Using Trane's kit, would my 8kw generator still be able to start the AC unit up, as it can currently using the supco cap?

  8. #8
    Join Date
    Sep 2009
    Location
    Stumptown,USA
    Posts
    1,251
    The Trane hard start kit is designed just for your compressor. An electrical engineer at Trane has done the calculations to have that factory hard start kit engage the start relay (putting the start capacitor in the circuit) at the exact pickup voltage and disengaging the relay at the exact dropout voltage for YOUR compressor to ensure maximum longevity. That is why Trane does not allow you to use universal/aftermarket start devices OR YOU VOID YOUR WARRANTY. Excess heat in the compressor motor windings shortens compressor life.
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  9. #9
    Join Date
    Jul 2012
    Posts
    7
    Hey guys thanks so much for being apart of the conversation. Just want to make sure I put $$$ to good use.

    New information:
    Came home from church and noticed the temperature in the house rising slowly. AC comp wasn't spinning but fan was. Opened up the unit and found that the supco was really hot. Took out the supco, put back in old 5-2-1, AC comp came up. I should have tried starting unit without the 5-2-1 but was more interested in getting unit back up.

    So supco over heated in about 24 hours. Will take your advice and look for a 5-2-1 relay style hard start. I here the Kickstart is pretty good(?). Else I guess I'll be trading in this generator for it's bigger cousin.

    You guys have definitely helped me out by setting my expectation. And not letting me get too excited over a too-good-be-true solution.

    Any additional advice would be greatly appreciated.

  10. #10
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,665
    Call a service company that sells trane andgive them the model number of the unit and ask them to come and install a trane start kit probably a 257 the problem with the supco is they will not rapidly restart a compressor you have to have a few minuets from start to start as the need time to cool

  11. #11
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,665
    Im wondering if the unit has a expansion valve ,also get the unit checked for other issues ,im thinking a complete tune up might be needed

  12. #12
    Join Date
    Jul 2012
    Posts
    7
    What your saying makes a lot of sense. Now that I've taken a moment to realize that the way these hard starts work via large capacitance is to allow higher instant current to flow across the start winding... resulting in higher heat build up in the supco cap. That's not helped by an on going heat wave. Also, since this isn't a true potential voltage relay, but a thermal based timer... That timer's proper function is bound to go off kilter if it's 105+ outside, and being subject to the higher brief current flows....


    Wow learned a lot. Going to call a Trane dealer in the morning and see what the proper kit options are. I'm an electical engineer by trade, and my AC unit was built in '98 so it's well outside warranty. Making for a good experiment / experience.

    I wonder if people ever consider having some sort of A/B switch to select a more aggressive current/torque for the startup coil for situations like the one I have... Needing to switch from pole power to generator power in the event of a blackout?

  13. #13
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Quote Originally Posted by Ngcreese View Post
    Now that i've put in a new albeit, generic start cap, I'm seeing the difference cause for sure the startup amps aren't coming from the generator, but being dumped back into the compresssor by the cap
    The start kit gives the compressor more starting torque, it doesn't "dump" any current back into anything.

    With a functioning start kit, the compressor still draws the same LRA it would without a start kit, just for a MUCH shorter period of time, down from a few hundred milliseconds to under 50 milliseconds.

    The dramatically shorter period of time the compressor pulls LRA is less of a kick in the teeth to your generator than it would be without a functioning start kit, so the compressor is able to get turning before the voltage from the generator drops too low.
    Once the compressor starts turning, the amp draw drops off very quickly.
    If more government is the answer, then it's a really stupid question.

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