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post #1 of 8 (permalink) Old 06-15-2019, 05:08 PM Thread Starter
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Air compressor newbie

Good afternoon (depending on when you read this).

I have two questions. While I say I am an air compressor newbie i am mechanically inclined to the point I break a lot of stuff. Kidding aside, I understand the mechanics of an air compressor but I don't know brand quality and very specific mechanical flexibility.

Without further ado:

Question 1. I just procured a Dayton Speedair 30 Gal, 2hp air compressor from a neighbor. Motor date code is B853 and model 3Z421E. What do I have? This will matter on question 2.

Question 2. The motor is a 115v/240v 2hp. It was not hooked up and power cord was cut at the motor. The person I got it from said he got it from another friend about 4-5 years ago and that the friend said it worked. Now I did not fall out of a turnip truck last night, it was actually the night before so I went into this assuming that I'd have to fix something - either the motor, the pump or both. While I noticed the dual voltage because I do not have 220 in the garage I assumed I was fine until I noticed the Amps were 24. I have 20a service to the garage. Should I A) - Hook it up anyhow, B) - Look for a smaller motor, C) - look for a smaller motor and smaller rated pump D) - just go buy a new one. Or is there something else I can do? Is it ok to hook up a smaller motor (1 or 1.5hp) to 2 hp pump?

Thank you for any advise you
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post #2 of 8 (permalink) Old 06-17-2019, 11:35 AM
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Dano,

As for hooking it up as is, you could try it on 120 volt with tank open (0 pressure) just to test to see if everything is working OK, but you could never use it for pressure without modification/adjustment. The only correct way to use a 120 volt circuit @24 amps in this case is to run 10 gauge wire to an approved 30 amp breaker, plug and socket. personally I would set compressor up for 240 volt and run a 12 gauge wire to an approved 20 amp breaker and socket. If the outlet in the garage is a single run (meaning no other outlets are daisy chained) to your breaker panel you could theoretically convert the line to 240V dual pole breaker and a 240 volt socket. But be warned I would only advise that an electrician or a qualified contractor should perform the conversion. In most houses single runs to one outlet are a rare bird. To save costs outlets are almost always tied together on single breakers to save construction costs, especially in the 50's era wiring. This would negate conversion option.

Stephen

Last edited by stevon; 06-17-2019 at 01:15 PM. Reason: Single line only
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post #3 of 8 (permalink) Old 06-17-2019, 11:59 AM
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Dano,

If your house circuit is in good order and you can trust your circuit breaker another option could be to use a smaller motor pulley and check amps with a clamp on ammeter (they are cheap at harbor freight)https://www.harborfreight.com/digita...ter-96308.html The smaller pulley would give the motor more leverage so less HP (amps) would be required to drive the pump. There are limits as to how slow you can run the pump for oiling requirements, check pump specs.
at 0 lbs pressure in the tank motor load (amps drawn) should be low 10 amps or so. as the pressure rises more resistance will be exerted on the motor by the pump requiring more HP from the motor (more amps) HP in electric motors is determined primarily by amps drawn
you could adjust pressure cutoff switch when you see the current approach 20 amps. say 80,85,90 lbs or so to set shutoff power to the motor. Stressing your wiring at 20 amps is not recommended.

Only drawing up to 80%of a circuit rating is recommended for normal and extended use.
20-amp Circuit example:

Total Wattage Capacity: 20 amps x 120 volts = 2,400 watts
Safe Wattage Capacity: 2,400 watts x 80% = 1,920 watts
Safe Amperage Capacity: 20 amps x 80% = 16 amps

Dano,

In any case using 120 volt for this compressor, you will be pushing the limits and stressing possibly old wiring, NOT recommended! buy a smaller electric motor https://www.harborfreight.com/engine...tor-67842.html + smaller drive pulley or wire the garage outlet correctly, the only sane choices!
by the way a smaller motor drive pulley is mandatory. If you use the 2 HP size pulley the load will try to get it out of a smaller motor regardless and current will raise to the same (24 amps) despite the lower rated HP motor, there are no shortcuts. I can help with pulley size required/recommended for lower HP drive motor

Last edited by stevon; 06-18-2019 at 12:51 PM. Reason: pulley size
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post #4 of 8 (permalink) Old 06-17-2019, 01:44 PM
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Dano,

I forgot to ask, what will you be doing with this compressor? inflate tires or auto body equipment? about 5 CFM is the most you can get out of a 120volt 20amp house circuit. If you need more CFM say for spray guns, sanders, grinders etc. that need 9 CFM or more you will never be able to get this much air power out of a 120volt 20 amp circuit!

Stephen

Quote:
Originally Posted by stevon View Post
Dano,

If your house circuit is in good order and you can trust your circuit breaker another option could be to use a smaller motor pulley and check amps with a clamp on ammeter (they are cheap at harbor freight)https://www.harborfreight.com/digita...ter-96308.html The smaller pulley would give the motor more leverage so less HP (amps) would be required to drive the pump. There are limits as to how slow you can run the pump for oiling requirements, check pump specs.
at 0 lbs pressure in the tank motor load (amps drawn) should be low 10 amps or so. as the pressure rises more resistance will be exerted on the motor by the pump requiring more HP from the motor (more amps) HP in electric motors is determined primarily by amps drawn
you could adjust pressure cutoff switch when you see the current approach 20 amps. say 80,85,90 lbs or so to set shutoff power to the motor. Stressing your wiring at 20 amps is not recommended.

Only drawing up to 80%of a circuit rating is recommended for normal and extended use.
20-amp Circuit example:

Total Wattage Capacity: 20 amps x 120 volts = 2,400 watts
Safe Wattage Capacity: 2,400 watts x 80% = 1,920 watts
Safe Amperage Capacity: 20 amps x 80% = 16 amps

Dano,

In any case using 120 volt for this compressor, you will be pushing the limits and stressing possibly old wiring, NOT recommended! buy a smaller electric motor + smaller drive pulley or wire the garage outlet correctly, the only sane choices!
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post #5 of 8 (permalink) Old 06-19-2019, 10:39 PM Thread Starter
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Stevon,

Thank you very much for the help. Do not intend to sound short. Had a long list of items i responded to that you asked about then promptly forgot my PW and everything reset.
So the cliff notes:
12ga wiring <1yr old
I had one original outlet so I ran this line.
2 outlets on 20a line. For convenience not for multiple uses - unless you count a very small clock radio
Cannot see running multiple items on the 20a line (or either line - original 15a and 20a). Normal would be just one of the following, table saw, sander, compressor, and, I'll correct myself, clock radio
How would I find min rmp for pump?
My usage would be 85% tires and blow gun - short burs for saw dust., 10% (maybe) small disc polisher. very light duty on this - no heavy grinding, and MAYBE 5% spraying cabinets if my HVLP goes out and only a few at a time not an entire kitchen job.

Sorry for short reply but Had 3 paragraphs before being wiped clean. Just tight on time now.

Very much appreciate all your help.

Thank you!
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post #6 of 8 (permalink) Old 06-20-2019, 11:34 AM
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3Z421E Plan and specs

Dano,

This is what I could find on the WEB:

3Z421E uses pump model# 2Z499
Speedaire-2Z499-2Z499C-Compressor.jpg of Igor's index of metalworking and electrical manuals
https://www.publicsurplus.com/sms/au...iew?auc=578887

Using this nifty tool I confirmed 1725 rpm electric motor drive pulley size is 3 1/4"
with pump diameter flywheel at 10"
https://www.blocklayer.com/pulley-belteng.aspx

pressure [email protected]
1.5 HP drive pulley size 3.250"
pump RPM 535

Quote:
Originally Posted by Dano2552 View Post
Stevon,

Thank you very much for the help. Do not intend to sound short. Had a long list of items i responded to that you asked about then promptly forgot my PW and everything reset.
So the cliff notes:
12ga wiring <1yr old
I had one original outlet so I ran this line.
2 outlets on 20a line. For convenience not for multiple uses - unless you count a very small clock radio
Cannot see running multiple items on the 20a line (or either line - original 15a and 20a). Normal would be just one of the following, table saw, sander, compressor, and, I'll correct myself, clock radio
How would I find min rmp for pump?
My usage would be 85% tires and blow gun - short burs for saw dust., 10% (maybe) small disc polisher. very light duty on this - no heavy grinding, and MAYBE 5% spraying cabinets if my HVLP goes out and only a few at a time not an entire kitchen job.

Sorry for short reply but Had 3 paragraphs before being wiped clean. Just tight on time now.

Very much appreciate all your help.

Thank you!

Last edited by stevon; 06-20-2019 at 05:02 PM. Reason: flywheel 10"
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post #7 of 8 (permalink) Old 06-20-2019, 12:06 PM
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Dano,

What we need to calculate pulley size is electric motor RPM and Flywheel diameter on pump if you want to use the 120 volt option, that will also require the use of a clamp on ammeter.
theoretically you can run the 2HP motor at a 1.5 HP load and current required would be the same as a 1.5 HP motor. the amp requirement is determined by the load, not the motor being used. As for the 240 volt conversion I would talk to an electrician or a friend who is qualified. Note if you convert the outlet to 240 volt nothing but a 240 device can be used on it. e.g. no radio, lights, etc.

Stephen

Quote:
Originally Posted by stevon View Post
Dano,

This is what I could find on the WEB:

3Z421E uses pump model# 2Z499
Speedaire-2Z499-2Z499C-Compressor.jpg of Igor's index of metalworking and electrical manuals
https://www.publicsurplus.com/sms/au...iew?auc=578887

Using this nifty tool I confirmed electric motor drive pulley size is 3"
https://www.blocklayer.com/pulley-belteng.aspx

pressure [email protected]
1.5 HP drive pulley size 3.125"
pump RPM 535
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post #8 of 8 (permalink) Old 06-20-2019, 12:22 PM
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Dano,

Since this sounds like you have a dedicated line and an additional 15 amp circuit for 120 volt needs. The 240 volt conversion of outlet and electric motor setting is the simplest and best result/path to follow.
Reasons:

1) smaller pulley + smaller belt change is not required
2) get the most CFM output available from this compressor
3) most efficient use of power available
4) most cost effective solution
5) no engineering or testing required
6) Only additional parts required is a dual pole breaker, 240v, 20amp socket and plug

Stephen
Quote:
Originally Posted by stevon View Post
Dano,

What we need to calculate pulley size is electric motor RPM and Flywheel diameter on pump if you want to use the 120 volt option, that will also require the use of a clamp on ammeter.
theoretically you can run the 2HP motor at a 1.5 HP load and current required would be the same as a 1.5 HP motor. the amp requirement is determined by the load, not the motor being used. As for the 240 volt conversion I would talk to an electrician or a friend who is qualified. Note if you convert the outlet to 240 volt nothing but a 240 device can be used on it. e.g. no radio, lights, etc.

Stephen

Last edited by stevon; 06-20-2019 at 02:29 PM. Reason: cost
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