Generator won't power compressor....ideas?

[joshuabardwell]

True, but 240V gens dont work that way. Full rated power is only available from the 240. 6500/240 = 27.5 is the amps available. Only half power will be available from each 120V leg of the spit since the gen will be fused to protect its windings from current over 27.5A. That compressor will never start on the 120V output of that 240V gen.
larry

Bingo. Saved me some typing.

 

[Boeing]

Can you help with the wiring of the 240 plug? The recep on the gen is a 4 prong with an L shaped for one of the prongs. My radial saw (don't know about the compressor motor yet) has fittings for THREE wires to go to 240V I did that years ago and used a THREE prong dryer plug. It ran GREAT...very fast and powerful. Anyway, if there are 3 fittings and 4 prongs for the generator......duh?

ANOTHER question that I've had for years......this compressor pressure switch cuts the compressor off at 120PSI but doesn't RE-start it until about 85 PSI. When I sand-blast, for example, I need at least 100 PSI or I'm wasting time and sand. IS there a way to make this compressor come on at 100 PSI?

The collective amount of knowledge in this group is AMAZING......I guess 10,000 guys averaging 45 years of acquired experience....WOW.

 

[chim]

take his 4hp peak #.. convert to watts.. then convert to rms, assuming that number is a peak watt rating.. now use the hp conversion and go back to hp... the numbers bang out almost perfectly.

so yes is does matter.. completely.

you just have to understand electronics and economics...

I do sorta understand electronics and economics. That's why I said the 4HP is a sales pitch calc. 4HP at a perfect power factor is approx 2.983KW. The full load curent the OP listed is 16A @ 115V at a perfect power factor is 1.84KW. There's no free lunch. The equivalent of 4HP cannot be produced at 115V and 16A. Buy yourself a good reference book and a Fluke and check it out.

 

[DarkBlack]

Real 4hp motors won't be available as 115v single phase versions. It makes no sense. My 5000/6250 generator tries to start my 230v 4hp compressor, but the elec motor stops when it tries to swich to run mode. It barely starts my 1hp 230v deep well pump. For the 1st full second the current maxes and holds at 30 amps, but at that point the gen voltage is down to 180 volts, and about 57hz. Then the pump comes up to speed and the current drops down to 9 amps. Of course deep well pumps have the added math of the long copper run. I beleive the B.S. "peak" hp ratings on shop vacs etc.. are calculated from locked rotor amps * voltage, which is very very misleading.Always go by the running amps * V.
I f you want to do one better look at the rpm at that amp rating. The lower below either 3600 or 1800 rpm's the more slip they have "allowed" for the rating and this increases the current draw. so the plot thickens...

 

[jenkinsph]

I suspect your electric driven compressor will always be hard to run on your genset. If you need a good portable compressor and portable power at the same time I would buy an engine driven compressor for those uses. I say this because the little pancake compressors have a nasty habit of auto starting at the same time you are using another large tool. I bought an Ingersoll-Rand T30 with a 30 gallon tank (or close to that) two stage 175 psi about 19cfm back in 1998 to run my portable air tools, been a good unit and satisfied with it. Unless your sandblasting is some type of miniature rig it seems your compressor would be too small.

Lots of bogus ratings on these little compressors and shop vacs, I remember a sales person trying to steer me to a 6hp peak shop vac with an 18/2 power cord 120v a few years back. That kind of misleading crap really turns me off. Most all 120v plug in appliances and tools are limited to 15 amps maximum draw that are sold in the US.

 

[dex3361]

Can you help with the wiring of the 240 plug? The recep on the gen is a 4 prong with an L shaped for one of the prongs. My radial saw (don't know about the compressor motor yet) has fittings for THREE wires to go to 240V I did that years ago and used a THREE prong dryer plug. It ran GREAT...very fast and powerful. Anyway, if there are 3 fittings and 4 prongs for the generator......duh?

ANOTHER question that I've had for years......this compressor pressure switch cuts the compressor off at 120PSI but doesn't RE-start it until about 85 PSI. When I sand-blast, for example, I need at least 100 PSI or I'm wasting time and sand. IS there a way to make this compressor come on at 100 PSI?

The collective amount of knowledge in this group is AMAZING......I guess 10,000 guys averaging 45 years of acquired experience....WOW.

You could make a 3 prong by 4 prong adapter for your generator or cut the end of the 3 prong plug off and put a 4 prong twist lock on the cord.

 

[Soundguy]

I do sorta understand electronics and economics. That's why I said the 4HP is a sales pitch calc. 4HP at a perfect power factor is approx 2.983KW. The full load curent the OP listed is 16A @ 115V at a perfect power factor is 1.84KW. There's no free lunch. The equivalent of 4HP cannot be produced at 115V and 16A. Buy yourself a good reference book and a Fluke and check it out.

you are either not reading my posts or totally not understanding them at all.

this is clearly a peak vs rms issue.

and YES.. it is an advertising issue.. they are saying 4hp to lure people in.. it's not an rms measurement.. and not what the user will or even could see based on how it is setup.

i've got plenty of lab and industrial grade meters and o-scopes.. and had the ticket for years...

 

[Soundguy]

ANOTHER question that I've had for years......this compressor pressure switch cuts the compressor off at 120PSI but doesn't RE-start it until about 85 PSI. When I sand-blast, for example, I need at least 100 PSI or I'm wasting time and sand. IS there a way to make this compressor come on at 100 PSI?

The collective amount of knowledge in this group is AMAZING......I guess 10,000 guys averaging 45 years of acquired experience....WOW.

it's a pressure switch like a well pump usually. there may be adjustable cut in / out points.. or it may be a set difference between cut in and out and only one adjustment.

if the later.. be carefull.. you can exceede the pressure rating.. so may not be able to set a high cut in.. by keeping cut out correct.

if both are adjustable.. just set cut in as desired..

 

[SPYDERLK]

Can you help with the wiring of the 240 plug? The recep on the gen is a 4 prong with an L shaped for one of the prongs. My radial saw (don't know about the compressor motor yet) has fittings for THREE wires to go to 240V I did that years ago and used a THREE prong dryer plug. It ran GREAT...very fast and powerful. Anyway, if there are 3 fittings and 4 prongs for the generator......duh?

ANOTHER question that I've had for years......this compressor pressure switch cuts the compressor off at 120PSI but doesn't RE-start it until about 85 PSI. When I sand-blast, for example, I need at least 100 PSI or I'm wasting time and sand. IS there a way to make this compressor come on at 100 PSI?

The collective amount of knowledge in this group is AMAZING......I guess 10,000 guys averaging 45 years of acquired experience....WOW.

4 prong provides for a true non current carrying ground, as well as the 2 HOTs adding to 240, and the neutral that allows splitting it down to two 120V circuits. Neutral can be connected to G potential at the gen, but you should ground the gen well or you will have a small charge on the gen when drawing from the 120 legs unevenly. If you operate only 240 tools this will not be a problem.

You can turn up the pressure switch on your compressor, but the top pressure will rise equally. The better pressure switches have a secondary adjustment that allows you to increase the OFF pressure span. If yours has this and is already adjusted to increase it to a 35psi span you will be able to decrease it to mabey as low as 30psi [which is the customary minimum].
larry

 

[SPYDERLK]

/

you are either not reading my posts or totally not understanding them at all.

this is clearly a peak vs rms issue.

and YES.. it is an advertising issue.. they are saying 4hp to lure people in.. it's not an rms measurement.. and not what the user will or even could see based on how it is setup.

i've got plenty of lab and industrial grade meters and o-scopes.. and had the ticket for years...

It may be peak vs RMS V x I computation, sure. But I think its more like the Torque x RPM max the motor is capable of before breaking to a stall. It will burn up in a few minutes at that level because it will be drawing over 2x rated current.
larry