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How to reduce start-up spike?

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minime

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I have an air conditioning machine (less than 1000w) which I have put into my van which is to be ran off an inverter (1500w), the problem is when the air con starts up it pulls too much power and causes the inverter to go into protect mode (even though its supposed to be 3000w surge)

I know it will run the air con as if you keep trying it will eventually start and run, its just the initial spike thats the problem. Does anyone know of a way I can get around this?

Any help much appreciated!
 
Take a look at this item:
https://www.grainger.com/Grainger/SUPCO-Hard-Start-Kit-4E240

The start-up inductive reactance of an AC compressor is particularly small, for a brief period of time. Consequently, the associated start up compressor current is greater.

The capacitor of the hard-start device would compensate or cancel the inductive reactance current spike, and then after a few seconds be excluded from the circuit. The overall effect would therefore be a reduction of the start up current magnitude.
 
Is it 12V or 24V inverter. If its 12V the current woulbe huge on start up & the leads from the inverter to battery would need to be very large & short. The battery may not be able to suport the peak current draw. A far better option is run it of a generator.
 
... Check your battery cable terminals for clean, bright, metal to metal connections .... as well as tightness of bolts and nuts.
You should have a fine wire brush, a supply of fine grade emery cloth, and a can of electrical contact cleaner spray.
A specialized battery terminal cleaning brush or tool is useful.
 
Is it 12V or 24V inverter. If its 12V the current woulbe huge on start up & the leads from the inverter to battery would need to be very large & short. The battery may not be able to suport the peak current draw. A far better option is run it of a generator.

I agree. Discounting the start a 1000 watt load on a 12 volt system is going to be about 84 amps. That does not even begin to take into consideration the loss of the inverter. Next a 1500 watt inverter would need a minimum of about AWG 2 wire gauge. Unless you are running some very large wire from the inverter to the battery I would venture a guess the inverter shuts down from low voltage. The use of copper welding cable comes to mind here. Assuming a 12 volt automotive system, and even if the system had a 100 amp generator the overall system will consume power faster and more than you can make.

Just My Take
Ron
 
dehumidifier

A 1 kW constant electrical load does seem excessive for a 12 v automotive system.
Consider getting a dehumidifier to run off of the inverter and 12 v battery bank.:
**broken link removed**

The dehumidifier also uses a freon compressor to achieve its dry air product, but it is more efficient than an AC compressor, and would not be running as frequently. Maybe it would have a battery current drain of something like 50 amps, compared to Reloadron's 84 amp figure, mentioned previously. Here again, the dehumidifier should not see as many compressor on hours as the AC unit.

The savings in gasoline used to recharge the batteries using a dehumidifier could be significant.

You might not have air conditioning, but you could maintain a reasonable comfort level ... if you don't open the doors too often.
 
Something else I forgot to mention. Unless this inverter outputs a pure sine it likely outputs a modified sine wave which the fan motor and compressor in the AC unit likely will not care for.

Ron
 
Debe/User_88: Its an electric inverter 12v to 240v. Its connected with heavy gauge car battery cable, all connections are sound, it has only just been installed.

User_88: The Hard Start sounds interesting, I will look into that further. Does it connect inline on the live input to the aircon?

Reloadron: Although the power output of the inverter is 1500w at 240v, I dont know believe it takes in 1500w from the 12v supply (althou I am not sure on this) as you say it would be such a high ampage there wouldnt be much point in having one. Also the problem is not voltage drop

I do have a really cheap inverter which is only 700w which actually manages to run the aircon for a while untill it gets too hot, but it manages to start it most of the time. Also I have tried a 1500w heat gun and it works fine.

Unfortunatly it is only a modified sine wave as I could not strech to the pure sine wave prices, but so is the 700w which runs it
 
Well on the bright side it is a 240 volt unit and not 120 volts. That will half the currents I listed, still high but not that bad. I would still question if it is an inexpensive inverter the output waveform. The inverter will only draw the power from the battery to support the load it is supporting.

Ron
 
Am I right in thinking the Hard Start is just a large capacitor? I'm guessing its so the motor/compressor will pull from this first and reduce the initial load pulled from the inverter? but wouldnt the capacitor be empty at switch on, thus adding to the load as it charges itself?
 
Capacitor goes in series with the start windings of the compressor. There is a Run winding & Start windings. It alters the phase to lower the start current.
 
Hi,

Anyone here ever try one of those little 'can' devices with the cap and relay? I was wondering how well they work on a 'regular' 120vac household line (not an inverter). Do they limit the surge a lot or just a little?
 
Capacitor goes in series with the start windings of the compressor. There is a Run winding & Start windings. It alters the phase to lower the start current.

Sorry about previous comment regarding the function of the Hard Start device. Debe is correct, in that the Hard Start capacitor is connected in parallel with the run capacitor, that itself is in series with the start winding inductance. The function of the hard start capacitor is therefore to add in parallel with the run capacitor, for a brief moment, and serves to shift the phase of the start winding current slightly so that there is added phase difference between itself and the main winding.
The result is an improvement in the start up rotational torque.

It looks like the Hard Start Capacitor is the same as the Start capacitor shown in Fig 11-26 below.
**broken link removed**
 
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