Capacitor Substitution


In one of my previous posts, I wrote about “Everything You Wanted to Know About Capacitors”, well, I didn’t give you everything I guess.

You all should know by now that you have to “match” the capacitance micro farad within the tolerance of the capacitor rating and that you can never go LOWER on the voltage rating.

Now, say you are at a job site and out of all the capacitors you have on your truck, none of them match and its 95 degrees outside on a Friday afternoon (or even worse — the weekend) and your customer HAS to have the air on because they are having a party.  What can you do to get the air conditioner going for your customer?

Actually, there is one of 2 options you have if you have an assortment of capacitors of various sizes.

The easiest thing to do is take a bunch of capacitors and wire them in PARALLEL.

As you can see by the diagram above, by wiring capacitors in parallel, the micro farad become ADDITIVE so a 10 μF capacitor PLUS a 30 μF capacitor gives you 40 μF.  The thing you need to be careful of here is that the VOLTAGE rating of the circuit is only as high as the lowest voltage rating of all the capacitors.  You can string together as many as you need to make the micro farad you need to get the unit going. (personal comment -if you want to simplify your truck stock, keep ONLY 440 volt capacitors on your truck.  Remember, you can always go higher but never lower)

The other thing you can do is to wire some capacitors together in SERIES.

The key to doing this is you have to use capacitors that have the same micro farad rating.  When you wire capacitors in series, the micro farad rating is “halved”.  The voltage rating is additive so the two 220 volt capacitors in the example above creates a 440 Volt 5 μF capacitor.

By either paralleling or putting capacitors in series, you can create the correct size capacitor you need to get the unit going.

In a lot of today’s units there are combination capacitors that handle both the condenser fan and the compressor.  You can still use individual capacitors for each component.  All you need to do is parallel the incoming power between the 2 capacitors and then just use the “discharge” of each capacitor to work with its component.  You do not parallel the capacitor outputs, only the inputs.

Now I think I have given you “Everything You Need to Know About Capacitors”. — I hope this helps!

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About yorkcentraltechtalk

I have been in the HVAC industry most of my life. I worked 25 years for contractors on anything from residential to large commercial boilers and power burners. For the past 23+ years I had been employed by York International UPG Division ( a division of Johnson Controls) as a Technical support/Service Manager but I am now retired. One of my goals has always been to "educate" dealers and contractors. The reason for starting this blog was to share some knowledge, thoughts, ideas, etc with anyone who takes the time to read it. The contents of this blog are my own opinions, thoughts, experiences and should not be construed as those of Johnson Controls York UPG in any way. I hope you find this a help. I always welcome comments and suggestions for postings and will do my best to address any thoughts, questions, or topics you may want to hear about. Thanks for taking the time to read my postings! Mike Bishop
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2 Responses to Capacitor Substitution

  1. Ken Urban says:

    So, this is where I get confused, series capacitors are 1/2 the rating, so, 2 440 volt caps, rated at 10 micro faraids become one 10 at 880?

    • Ken
      if you look at the example, when capacitors are wires in SERIES, the micro farad rating is HALVED. So 2 – 10 micro farad capacitors become 1 – 5 micro farad rating. the voltave rating is additive so the 2- 440 volts become 880 volts.

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