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Need help with PV to power an air compressor

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Posted by New Guy on May 16, 2015, 4:21 pm
  I have a HF 45 W solar setup charging 3 35AH batteries and a 2000/4000  
W inverter. I was hoping to power an air compressor which is rated for 14  
amps. As it is now it won't. How can I beef up my setup to do so.? I am  
new to PV and have trouble understanding electric talk. What do I need to  
add ? And can someone point me to a link which might help me to understand
a little about electricals associated with PV.


Posted by Vaughn on May 16, 2015, 5:16 pm
On 5/16/2015 12:21 PM, New Guy wrote:

Where do I start?

First, your 45 watt HF solar setup is likely barely good for 20 watts of  
actual charging in full sunlight.  Assuming no load, it will barely be  
enough to deal with the leakage current from those three batteries to  
keep them topped off.  Also, I would not trust the charging regulator  
that comes with that set.  If it under or overcharges your batteries, it  
WILL ruin them over time.

Second, you are trying to run a nominal 1700-watt load from a nominal  
2000 watt inverter.  Even if you can believe ratings, that leaves  
virtually no cushion for the unexpected.  There are lots of reasons why  
that might not work!  The inverter may not be heavy enough to handle the  
motor starting load, and/or the compressor motor may not like the  
(likely square wave) waveform from the inverter.

Are your battery cables short?  Are they heavy enough to handle the  
starting load of that compressor, which will be at least 300 amps on the  
DC side?

Honestly, to do what you want to do with solar power you need to start  
all over.  You need far more and better solar panels with an appropriate  
charge controller, you need a much better inverter, and likely you need  
heavier batteries and cables.

Posted by New Guy on May 16, 2015, 7:38 pm
 On Sat, 16 May 2015 13:16:00 -0400, Vaughn wrote:

    I hadn't considered waveform factor.      

  Cables are 2 ga. and approx 12" ( from terminal to terminal ). The 2 ga.
 cables to the inverter are about 24" to keep a little distance from the

  Originally I purchased the above to get lights in my barn and a possble
 powertool from time to time. I had 1 35ah battery which I bought at
 Northern Tool. I guess I figured that more batteries meant more available
 power. So I added a couple more of the same batteries.

  I do intend to purchase better panels some day. I was just hoping to
 get the most out of what I already had.  




Posted by Jim Wilkins on May 18, 2015, 10:13 pm
What is your experience / evidence for that?

Trojan disagrees:
"Generally, gel and AGM batteries have about 20% less capacity, cost  
about two times more, and have a shorter cycle life than comparable  
flooded lead acid batteries."

I've had better luck desulfating and equalizing old flooded batteries,  
as old as 2000 and 2002, than with 5 - 6 year old VRLAs.


Posted by clare on May 18, 2015, 10:53 pm
 On Mon, 18 May 2015 18:13:16 -0400, "Jim Wilkins"

Much better go buy the biggest 6 volt batteries you can buy and
connect in series for your required voltage. I'd be going at least 24
volts for that kind of load to reduce the primary current required.

2 big sixes in series for 12 is a lot better than 2 big twelvess in

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