I have a really good air compressor that has a 3 phase 3 HP motor that turns 1800 RPM. We are moving and will no longer have three phase. I have been looking for a replacement motor and have noticed that most of them are 3450 RPM. Wonder why that is the case. !750 RPM are available but not near as many as the higher
3 HP compressor motor-single phase
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James-W
Well-known member
Get a 3450 RPM motor and change the pulley size and belt to get the speed that you want.
Not cheap
https://www.amazon.com/dp/B000A7PP26/?tag=atomicindus08-20
Sent from my SM-N960U using Tapatalk
https://www.amazon.com/dp/B000A7PP26/?tag=atomicindus08-20
Sent from my SM-N960U using Tapatalk
strutaeng
Well-known member
I've seen more 5HP than 3HP for sale in the used market. Most are 1725 RPM in both of those HP ratings.
If you happen to find a 5 HP instead, you can install that also without changing anything else. Motor would just draw less amps, comparable to the 3 HP.
I've got an air compressor with a Curtis pump 7.5-10 HP. Motor is 10HP, but reduced with pulley so that it is runs as a 7.5 HP.
Even that is way too much for things like DIY pneumatics. I only fire it up when using HVLP air hog.
Anyway, point is that a larger HP would also work if it is cheaper to buy.
If you happen to find a 5 HP instead, you can install that also without changing anything else. Motor would just draw less amps, comparable to the 3 HP.
I've got an air compressor with a Curtis pump 7.5-10 HP. Motor is 10HP, but reduced with pulley so that it is runs as a 7.5 HP.
Even that is way too much for things like DIY pneumatics. I only fire it up when using HVLP air hog.
Anyway, point is that a larger HP would also work if it is cheaper to buy.
Just match the frame size, hp and RPM. Then it will bolt on with no other changes.
Guessing you are finding 3450 motor because you are searching for "air compressor motor". The cheap compressors often use them. It's just a motor, match the stuff above and you will be fine.
Guessing you are finding 3450 motor because you are searching for "air compressor motor". The cheap compressors often use them. It's just a motor, match the stuff above and you will be fine.
alfredeneuman
Well-known member
Aceman
Well-known member
Please explain how you came to this conclusion
A 5hp motor driving 3hp of load will draw similar current as a 3hp motor driving 3hp of load.
sparky 1971
Well-known member
sberry
Banned
I have a 3 and a 5. The 3 is the master and don't even have the breaker on to the 5, its demand/backup and I so rarely need it no reason to leave the power on. I got 200 gallons of tanks, air on 24/7. Leaves me with longer run times with a bit smaller motor, easier starts on rural lines. 4 minute recharge cycle.
3 of old were mechanic compressors, air tools, pumping tires including hi pressure truck tires. 5 became more popular with 100A service and body work. The price narrowed, standards and expectations went up, 5 has become the benchmark.
3 of old were mechanic compressors, air tools, pumping tires including hi pressure truck tires. 5 became more popular with 100A service and body work. The price narrowed, standards and expectations went up, 5 has become the benchmark.
sberry
Banned
2 stage, 5 hp 80 gallon tank can do most work a man can do, recharges fast, will outfit several mechanics, will do the body work for one man continuous. 2 men can share in a small shop, have seen a lot done on a 5. Normally doing a calc, 7.5 for 2 and 10 hp can do 3 or 4 pretty easy not counting 100% cap sandblast.
sberry
Banned
I did a setup on a truck shop. It was a bit of a challenge come to air to reason with the new owner that it was great we had 25 hp comp we didn't need to pipe everywhere 1.5 inch. Didn't need to go everywhere the same circuit on huge pipe.
strutaeng
Well-known member
HUH?
Amp draw is a function of work done. So if the pump, rpm, pulley are kept the same, the CFM produced will be the same for both motors, i.e, the "work done" is same.
Say the 3HP is drawing "X" amps. The 5HP will draw similar amps. There's torque curves, efficiency, etc., but in round numbers both will be similar.
The 5HP is not working at full capacity, therefore not drawing full amps.
The air compressor I mentioned has continuous-run mode. When the tank gets full, the pilot valve sends air to the the pump head and the compressor "free-wheels." I've checked with ammeter and it's drawing like 1A because it's not pumping air.
I'm not an electrician, just stating the basic physical theory.
alfredeneuman
Well-known member
What about this?
If it's a 5HP motor you'd need to install wiring suitable for 5HP in order to meet Code.
Maybe slightly less amps, but not simply 3HP's worth of amps.
The lighter loaded 5HP motor will have a worse power factor. (i.e. 'wasted' amps). The circuit would still need to be sized for the 5HP motor's FLA.
wyliesdiesels
Well-known member
In the US, the circuit wire needs to be sized by table 430.248 and the motor HP. for 5HP this means 28a and #10 THWN or #8 NM-b
nadogail
Well-known member
Quote:
Originally Posted by u2slow View Post
Maybe slightly less amps, but not simply 3HP's worth of amps.
The lighter loaded 5HP motor will have a worse power factor. (i.e. 'wasted' amps). The circuit would still need to be sized for the 5HP motor's FLA.
If your compressor use is minimal and your power is cheap (like Solar) maybe the waste due to power factor will be of little or no consequence.
Originally Posted by u2slow View Post
Maybe slightly less amps, but not simply 3HP's worth of amps.
The lighter loaded 5HP motor will have a worse power factor. (i.e. 'wasted' amps). The circuit would still need to be sized for the 5HP motor's FLA.
If your compressor use is minimal and your power is cheap (like Solar) maybe the waste due to power factor will be of little or no consequence.
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Good thing power isn't billed by amps. We pay for watts which is the real power used.
Power factor doesn't have a billing consequence (in residential, typically), but the circuit is still subject to a higher current, and that may require larger wire; despite only pulling 3HP out of the 5HP motor.
Neato. In Canada we size by motor FLA. When the equipment isn't there, then we use the HP table.
Neato. In Canada we size by motor FLA. When the equipment isn't there, then we use the HP table.
VFD and use the motor you have..........
Some say compressors and VFD are a bad combo............yet there are dozens of posts where they function just fine. Others say the VFD should be over sized for compressor use. Either way it an affordable option.
https://www.automationdirect.com/ad...ives_(vfd)#Horsepower_Rating_ms="3hp"&start=0
Some say compressors and VFD are a bad combo............yet there are dozens of posts where they function just fine. Others say the VFD should be over sized for compressor use. Either way it an affordable option.
https://www.automationdirect.com/ad...ives_(vfd)#Horsepower_Rating_ms="3hp"&start=0
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csp
Well-known member
VFD definitely has to be oversized for compressor use.
It's only viable vs a single phase motor if you buy a super cheap VFD. I've been down this rabbit hole and concluded the single phase motor makes the most sense. I also don't have to worry that it's been set up correctly and wait to see if either the motor or VFD let their smoke out on initial power up.
A 3hp, single phase motor is not hard to find.
It's only viable vs a single phase motor if you buy a super cheap VFD. I've been down this rabbit hole and concluded the single phase motor makes the most sense. I also don't have to worry that it's been set up correctly and wait to see if either the motor or VFD let their smoke out on initial power up.
A 3hp, single phase motor is not hard to find.
alfredeneuman
Well-known member
sberry
Banned
I used to fool with every gadget they made and in the end cost more and sometimes never really got done or done right. If I could and the start would work would be looking for a single phase, could even plug it in at 3 hp.
csp
Well-known member
It's not the number of wires, it's making sure they are on the correct terminals that I would be concerned with. Especially with instructions written in Chinglesh and the fact that none of these VFDs have standardized terminals or labeling. There's also the options of making sure that reverse is locked out, soft start, etc. There's a bit more going on than just connecting five wires + ground.
A three phase disconnect isn't relevant if you are swapping to a single phase motor.
alfredeneuman
Well-known member
All the drives I've hooked up were clearly labeled L1, L2, (and where used) L3 for the line side and T1,T2,and T3 for the load side.
They come with a basic default program setting, which is enough for a compressor that doesn't need bells and whistles like computer inputs.
Low quality no name ChiCom drives tend to have manuals that are written with the help of a Chinese to English dictionary. The better quality drives have their manuals written in grammatically correct English.
They come with a basic default program setting, which is enough for a compressor that doesn't need bells and whistles like computer inputs.
Low quality no name ChiCom drives tend to have manuals that are written with the help of a Chinese to English dictionary. The better quality drives have their manuals written in grammatically correct English.
All the drives I've hooked up were clearly labeled L1, L2, (and where used) L3 for the line side and T1,T2,and T3 for the load side.
They come with a basic default program setting, which is enough for a compressor that doesn't need bells and whistles like computer inputs.
Low quality no name ChiCom drives tend to have manuals that are written with the help of a Chinese to English dictionary. The better quality drives have their manuals written in grammatically correct English.
If I can wire a 3 phase motor to a one phase 230 vac VFD (KBAC-27D), then anybody can. It's pretty simple, even I could figure it out.
2x72 belt grinder with a Weg 2hp motor. Not saying that's the way to go for a compressor. But for a 2x72 belt grinder, it's the shiznit.
csp
Well-known member
Since the sub-point about wiring (taken out of context) seems to have a life of its own, my main point was you can get a quality 3hp, single phase motor for less money than a cheapie (read questionable life), appropriately sized VFD.
I'd be all for a VFD if we were talking about a use that variable speed were beneficial.
I'd be all for a VFD if we were talking about a use that variable speed were beneficial.
alfredeneuman
Well-known member
csp
Well-known member
It's out of context because you turned correct wiring into the reason for or against using a VFD. The main reason I stated no on using a VFD is cost. Getting the wiring done correctly wasn't the driver, it was a hitchhiker that happened to be riding along.
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sberry
Banned
Agree, the cost and just more **** in the line.
marinusdees
Well-known member
All the drives I've hooked up were clearly labeled L1, L2, (and where used) L3 for the line side and T1,T2,and T3 for the load side.
They come with a basic default program setting, which is enough for a compressor that doesn't need bells and whistles like computer inputs.
Low quality no name ChiCom drives tend to have manuals that are written with the help of a Chinese to English dictionary. The better quality drives have their manuals written in grammatically correct English.
"Grammatically correct" does not translate as "intelligible"..At least not to an old fart like me.
alfredeneuman
Well-known member
I said it in response to the "Chinglesh comment"
The manual's written in plain English
Judge for yourself
https://www.vfds.com/manuals/hitachi-sj200-manual.pdf
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marinusdees
Well-known member
I said it in response to the "Chinglesh comment"
The manual's written in plain English
Judge for yourself
Holy s---. I haven't got time to read nor can I understand all this stuff. Even if I was an EE, given the era I'm from I don't need all this . And, I have 9 years of education beyond High School. Guess I wasted my money or have a pea-sized brain, you choose. And, I have four VFDs in my shop. Makes me a kind of a genius, maybe.
You are obviously several intelligence levels above me. I'm totally in awe.
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csp
Well-known member
I said it in response to the "Chinglesh comment"
The manual's written in plain English
Judge for yourself
So in my first post which started this back and forth I specifically said super cheap VFDs would be the only way to financially make it viable to use a VFD. You equate that to mean Hitachi?
Again, more context loss.
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alfredeneuman
Well-known member
So in my first post which started this back and forth I specifically said super cheap VFDs would be the only way to financially make it viable to use a VFD. You equate that to mean Hitachi?
Again, more context loss.
NoThe better quality drives have their manuals written in grammatically correct English.
That was an example of one of the better drive manuals, not the Chi-com cheapo written in as you say "Chinglesh"
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csp
Well-known member
Clarifying the irrelevant
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alfredeneuman
Well-known member
sberry
Banned
Living proof if some threads go on long enough they turn to ****.
csp
Well-known member
Do I? The relevant context is cheapo VFDs for their price of entry vs a new motor and the manuals that accompany them. We all know that there are better VFDs out there. We all know that these better VFDs likely come with better documentation. WE also know that there's a cost associated with that which makes them not such a good option for the OP's situation. You may as well have just suggested the OP get a new compressor. It would have had as much value.
Call it reading comprehension if that means you can't go beyond the latest reply in mind at any given time. I'll call it staying on topic.