Sizing a start capacitor for a cabonator motor

Fist things first; I am a carpenter. Motors and machining are not my forte. I am posting on here looking for some advice with a specific problem.
I am part of a crew of folks that run a food booth at an annual festival in Oregon. Our booth site does not have AC power and we aren't allowed to run a generator. Normally this isn't a problem. We use ice (lots) for refrigeration. We use 12V to pump water and power lights, etc.
One of the items we sell is soda. For years we force carbonated each keg using CO2; rocking each keg until it was saturated. I/we have dreamed of making this less labor intensive. We would like to power a carbonator pump reliably with a battery bank and an inverter. We have tried this in the past and been frustrated. Attached are pics of the pump unit we are using and a close up of the motor spec label. The motor is listed at 6.5amps when running, but at startup it has to overcome the resistance in the pump which causes the amperage draw to spike momentarily to approx. 18V as observed on our inverter's display. I believe its this spike that has has wiped our battery bank out in the past.
Is there a way to improve this circuit with the addition of a start capacitor? If so how do we select the right start cap, and how do we integrate it into the circuit? Any advice would be really appreciated.
To be overly clear- We can round up large batteries. We have even used big 8D marine batteries in the past without reliable success. We do not presently have a way to charge these batteries at our booth. I would love to have some PV that would trickle charge our battery bank, but that is another project. Would a start capacitor help make this system operate, or is this a case of "no free lunch"?
Cheers and Thanks,
Joel

The motor, if it runs from wall power when tested, has everything it needs. No extras required.

Starting that motor may require a surge of over 30A. Motors are like that. if the inverter cannot supply that surge, then it will not start. Starting with a pump full of material is unlikely to help, and may raise the current needed.

The batteries are virtually certain to be OK, the surge is unlikely to damage them. You may need either a smaller motor, or a larger inverter. Possibly the wires from the battery bank are too small for the current, you likely need 3/0 or 4/0 wire to minimize voltage drop. I would suppose that you might have 300 to 500A surge, depending on the current the motor needs, etc, and you cannot afford much voltage drop in the wires,.

BlazingSalads said:

///We would like to power a carbonator pump reliably with a battery bank and an inverter. W

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Hey Joel... rather that taking DC power from your 8D batteries, converting it to 120vac with an inverter, then running a 120vac induction motor, why not simplify it a whole lot, and use a more direct path.... replace the carbonator motor with a DC motor?

And a question of opportunity- How LONG does that carbonator run, over a given period of time... to do what you need? Is it running continuously, or half the time, or a few minutes an hour? 10 seconds at a time?

If it's only running part-time, then going to a much smaller motor, and increasing the run time, would be a better move.


What's the possibility that this 'event' is a 'environmentally-friendly/home-grown/organic/off-the-grid' type event?

If so, another way to do it, is to mount that carbonator pump on an Air-Dyne chassis and invite your customers to get some exercise... ;-D

it might be helpful if you described the nature of the "lack of success" you are experiencing with the battery/inverter setup, and detailed the components you have tried. does it fail to start at all, or is it just not lasting long enough?

one problem with the "different motor" solution is the mount of the carbonator pump is rather specific to these motors.
yes, its easy for a clever(-ish) machinist to adapt anything that turns to it, but...

also, the duty cycle may be low ( =it only runs a few minuets at a time), but that does not necessarily mean a much smaller motor would work because a certain pressure threshold, about 100 psi I think, is needed for the carbonation to take place quickly.

a larger inverter is the answer I think.

no, a capacitor won't help, the "capacitor start" motor is a different type of motor, and it is wired differently to use that method to start rotation, the actual energy stored in the capacitor is minuscule to nonexistent (you can start a capacitor start motor that has never been plugged in, or has been stored for years, right?)

a bit off topic, but that is the same type of motor/pump used on many TIG coolers, and for that, those motors ARE ridiculously overpowered and inefficient.

that got me thinking and doing a little searching... it seems that some hot water circulating pumps may use the same split ring/slotted shaft mount, and they are available in various HP ratings.

that would be a fairly easy swap, the problem is if you spent 150$ on a say 1/6 hp motor, and it didn't work, you are out the dough and are back to SQ1..

do you know someone at a heating/plumbing supply that would let you try one out? run it on wall power first just to see if it works, and let us know if you do, good luck!

I just checked the carbonator pumps I have, and one is 1/4 HP and 5A, Marathon electric (I just assumed they were all 1/3), SO we can be fairly certain one quarter horse works. not a huge energy saving, but 23% or so!

JST said:

The motor, if it runs from wall power when tested, has everything it needs. No extras required.

Starting that motor may require a surge of over 30A. Motors are like that. if the inverter cannot supply that surge, then it will not start. Starting with a pump full of material is unlikely to help, and may raise the current needed.

The batteries are virtually certain to be OK, the surge is unlikely to damage them. You may need either a smaller motor, or a larger inverter. Possibly the wires from the battery bank are too small for the current, you likely need 3/0 or 4/0 wire to minimize voltage drop. I would suppose that you might have 300 to 500A surge, depending on the current the motor needs, etc, and you cannot afford much voltage drop in the wires,.

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We are using fat wires (diameter of my thumb) not sure of exact gauge. I will check with my compadre about inverter specs. These are good reminders. Thank you

Sometimes the easiest solutions are the best. At first search I am not finding a DC motor to swap into this pump. Do you have a suggestion as to where i should look?

It definitely works for a limited time and then the batts fail to get the motor started. The inverter alarm will go off. "Buzz", The tech at McCann's (manufacturer of carbonator)wrote and told me that the pump and motor are designed to run for extended periods if the water supplied to unit is of proper pressure (50-55psi. min 3/8" line)

I can go into my local ferguson and ask. I can also ask my plumbing subs, they might have something in their "collection".

Yep, This is for the Oregon Country Fair. This is the 50th year of Fun.

BlazingSalads said:

It definitely works for a limited time and then the batts fail to get the motor started. The inverter alarm will go off. "Buzz", The tech at McCann's (manufacturer of carbonator)wrote and told me that the pump and motor are designed to run for extended periods if the water supplied to unit is of proper pressure (50-55psi. min 3/8" line)

Click to expand...

Then it DOES start the motor? But it only runs for a short time? That is not what I got from the original post, but OK.......

How much battery capacity?

If the motor draws 6.5A, then you can figure the draw from the batteries will be somewhere around 70A +-. If you have 210 ampere hours of capacity, then you will probably get about 2 hours run time. After that, the battery voltage under load will probably be too low for the inverter, even though you might think you have another hour before it is "empty". The 210 AH is approximately the capability of two Trojan T-105 golf cart traction batteries (each 6 v, so used in series for 12V)

You do not want to run batteries to "empty", it is bad for them. And, the inverter will not let you. Figure on discharge from 100% to 25% as all you can/should do, and that then you need to put all that back into the battery, which means a heavy charge.

To replace 75% of capacity, you need to charge until about 90% of the charge is replaced, in ampere-hours (A-H), figuring you need 20% extra for losses. So a 10 hour charge for 75% of 210 ampere hours would need .about 19A of charge on average, for 10 hours. That would allow about 2 hours of run time on battery power, Add sets of two batteries per the above to get more run time. Also add the amperes charge, so two sets would be 420 A-H, three would be 630, etc. Run times would be 4 nd 6 hours, charge 38 and 57A for 10 hours.

As you see, there is no free lunch. And batteries are big and heavy.

How long do you need to run per day?

Would this 12VDC system be adaptable to your use?

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