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Author Topic: Running a milking machine from a battery  (Read 5736 times)
Greenbeast
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« on: July 03, 2019, 01:37:54 PM »

I have a 1/2hp vacuum pump, what size inverter would be safe for running this off a 12V battery?
It needs to run for 5-10 minutes, probably once a day, i think i worked out i could milk a few times before charging


edit: i realise this might be better in the battery/inverter section...
« Last Edit: July 03, 2019, 04:55:24 PM by Greenbeast » Logged
oliver90owner
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« Reply #1 on: July 03, 2019, 05:12:55 PM »

Depends on a couple of things.

Is the motor started under load and the quality of your inverter (like how much overload would it stand and for how long).

It would need about 375W if the motor was fully loaded, drawing nearly 40A from the battery dependent on the efficiency of the motor and the inverter (I assumed 90% for each) from the battery, but I doubt that is the case.  However the starting current will be rather in excess of that - likely by 3 times, perhaps more.

If it is an automotive type battery, donít leave it discharged too much for too long, either.

Unless a very temporary meaure, I would be using a genny.

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Greenbeast
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« Reply #2 on: July 03, 2019, 07:31:03 PM »

Depends on a couple of things.

Is the motor started under load and the quality of your inverter (like how much overload would it stand and for how long).

It would need about 375W if the motor was fully loaded, drawing nearly 40A from the battery dependent on the efficiency of the motor and the inverter (I assumed 90% for each) from the battery, but I doubt that is the case.  However the starting current will be rather in excess of that - likely by 3 times, perhaps more.

If it is an automotive type battery, donít leave it discharged too much for too long, either.

Unless a very temporary meaure, I would be using a genny.



It it directly connected to the vacuum pump by a 'flexi-shaft' type arrangement, so it certainly is not off-load and then subsequently introduced.
What size inverter should i be looking at?
Do i need pure sine wave or would modified be fine?

This would be a long term solution. I do not want a genny. She may not care but she also may not take lightly to an engine by her arse while i'm milking. That's without the purchase cost, the maintenance and faff of keeping a one, the pulling it out every time i need it.
I'm thinking of using my garden trolley with my milking bucket, the motor/pump, battery and inverter. Then i can wheel it back to mains power to charge.
On a very minimal budget
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biff
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« Reply #3 on: July 03, 2019, 08:09:33 PM »

Hi GB
     In little jobs like this you always need more than you think. I would try s 1000watt modified sine wave inverter and s couple of 100ah  batts to begin with. Pure sine wave is very sore on the juice and twice the price.  You will need a strong trolley because the batts will weigh between 60 to 80 kg. Use solid rubber 200mm wheels. The modern 250mm pneumatic wheels are all the time getting punctured. This time of year a 50watt  x 12v PV panel could keep the lot topped up and you could have it stuck on the wall outside and a long lead to the batts inside.
        Biff
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Greenbeast
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« Reply #4 on: July 03, 2019, 09:02:40 PM »

Hi GB
     In little jobs like this you always need more than you think. I would try s 1000watt modified sine wave inverter and s couple of 100ah  batts to begin with. Pure sine wave is very sore on the juice and twice the price.  You will need a strong trolley because the batts will weigh between 60 to 80 kg. Use solid rubber 200mm wheels. The modern 250mm pneumatic wheels are all the time getting punctured. This time of year a 50watt  x 12v PV panel could keep the lot topped up and you could have it stuck on the wall outside and a long lead to the batts inside.
        Biff

I saw the pure sine waves were more expensive, so that's good to hear. And i've been looking at 1000W. Will try with one battery for a start
I have a trolley that's rated for 350k and have had a fair bit in it. But the wheels are shoddy, i've replaced them all more than once, cheap chinese pressed steel and minimal welds. Tyres seem to do alright.
Unfortunately the milking station is under an oak tree, so no easy way to solar charge, might as well use the mains back at the yard

Thanks
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rogeriko
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« Reply #5 on: July 03, 2019, 09:14:27 PM »

very difficult to make this work properly. Just leave the vacuum pump plugged into the mains and run a long thin ptfe pipe out to the milking station.
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Greenbeast
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« Reply #6 on: July 03, 2019, 09:23:22 PM »

very difficult to make this work properly. Just leave the vacuum pump plugged into the mains and run a long thin ptfe pipe out to the milking station.

Why do you say that?
I think a long pipe combined with no buffer tank and and ancient pump will not make for the most consistent vacuum.
Also, it doesn't seem much different to running the extension leads, at least they wind up easily!
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biff
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« Reply #7 on: July 03, 2019, 09:24:49 PM »

OR,
  





   The alt is 150amp. delivers 100amp ticking over. Ticking over on the lowest factory setting shows 14.7 volts with no effort, runs drills and grinders.
  start it up and then shut the choke off and the fuel supply. It runs for 120 seconds or 2 whole minutes on the full of the bowl.
 It is quiet and the latest engine dampers seem to have smoothed out the engine vibration. It has an onboard sla 65amp battery.
 This could be your answer for the winter months. It would also be an excellent project for you.
                                        Biff
  Running that modified sine wave inverter is only a side show. The main aim is to fill a decent sized battery bank quick and then shut down until needed again or the bank voltage shows 123.5 under load.
  It,s about saving fossil fuel.
« Last Edit: July 03, 2019, 09:28:46 PM by biff » Logged

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ecogeorge
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« Reply #8 on: July 03, 2019, 10:07:33 PM »

very difficult to make this work properly. Just leave the vacuum pump plugged into the mains and run a long thin ptfe pipe out to the milking station.
Afraid this is not an ideal answer -vacuum drop is dependant on cross section area of tube and airflow.
Assume this is a portable (goat) milker ??  -you will want approx 50litres/min airflow at your working vac level (46 kpa ) ??
can be measured with airflow gun .........
Long vacuum tubes = vacuum drop.
what about a suitcase type genny -v quiet .......
George  ............(Delaval trained milking machine engineer)
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marcus
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« Reply #9 on: July 03, 2019, 10:19:47 PM »

Guessing it's an induction motor - theoretically 7* rating amps to start, but as the inverter output will sag under load it will be a lower but longer duration start up surge so ~2kva peak output should manage it. I'm guessing the vacuum is at least partially lost when the motor's off so it's not having to start under full load.

But really boils down to the quality of the inverter: a 1kw with 2* surge capability 'ought' to suffice but some are a lot better than others - some will let you exceed their surge rating for a second or two, others throw a tantrum the instant their peak rating is exceeded. Low frequency (big transformer inside) is best; pure sine would be more efficient (in theory) due to the power factor of the motor but a well designed MSW would work OK.

375w (~40A) for 10mins is ~7Ah so you could get away with a regular car battery as long as you recharge after every use (you should do that anyway with lead acid). The battery must have a good CCA for the startup surge, so a healthy car battery rather than a tired old lesure battery would be my choice.

are you sure it wouldn't be easier to train the cow(?) to a halter and lead her to the milking parlour? Or milk by hand?
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TT
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« Reply #10 on: July 03, 2019, 10:44:35 PM »

Where is the unit in relation to any outbuildings with power?
As an earlier post, suitcase Honda inverter generator.

I wouldn't be using car alternators etc.

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biff
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« Reply #11 on: July 03, 2019, 11:28:17 PM »

 To quote TT,
        "I wouldn,t be using car alternators. etc"
    There was a time that I would fully agree with that statement but these days car alternators have come a long way from the puny little efforts of the old days.
   Of course it all depends on the car alternator and of course it would be a fairly up market car with big power demands and an alternator that has to supply it for 100s of thousands of miles with out a break.
 The controllers are miracles in miniature with duel internal fans and all kinds of very very reliable do das. I am somebody who swears by the PMGs That can supply the basic raw electricity with the utmost reliability. You simply cannot beat the PMGs but there are certain car alternators that really dish out the power and do it in such a confined space without dump loads or any distractions.  I will eventually fit this one of mine with a Honda gas conversion. not because it is cheaper than petrol, (it,s not) but because it is greener and cleaner with absolutely no carbon footprint. (after the bottle and the engine)
   This was an exercise in economy balancing the engine with the output of the alternator. I have done this in 120vdc in PMG diesel driven with very good results. But the parts that go to make up the small petrol charger are readily available under our noses and we never think to use them..There are 100s of people on Utube doing this kind of thing but they go at it half hearted and get a half hearted result.
 The correct alternator is essential for good results. I got a real buzz out of building this machine. Some folks fly kites or go surfing, I futter at these kind of things and find it really rewarding.
                                   Biff
   
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chasfromnorfolk
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« Reply #12 on: July 04, 2019, 07:58:45 AM »

Regardless of how this thread runs GB, please let us know the outcome Ďin the fieldí. Itís the most charming image to emerge from Bodges for some time.

Chas
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oliver90owner
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« Reply #13 on: July 04, 2019, 12:30:34 PM »

Car alternators are notoriously inefficient - falling to about 50% when hot.  Donít know what efficiency, when cold.  Easy enough to recharge the battery using PV in the summer months, but winter insolation is pants!

I think Marcus may be close when putting actual figures on it, except that running battery current should be quite a bit lower, but simply starting machinery attached to the motor will be a load at start-up.  

Another question might be what type of motor is it?  I expect it is a single phase induction motor.  Soft start (even a 3 phase motor with VFD) might be good.    As stated before, starting and recharging is the bottle-neck of any system like this.  A Lister D, driving the pump directly, might be a better (more efficient) option!

The pump is only a 1 bar (14psi) compressor rated at 50l/min, after all.
« Last Edit: July 04, 2019, 12:34:06 PM by oliver90owner » Logged
Greenbeast
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« Reply #14 on: July 04, 2019, 12:33:36 PM »

very difficult to make this work properly. Just leave the vacuum pump plugged into the mains and run a long thin ptfe pipe out to the milking station.
Afraid this is not an ideal answer -vacuum drop is dependant on cross section area of tube and airflow.
Assume this is a portable (goat) milker ??  -you will want approx 50litres/min airflow at your working vac level (46 kpa ) ??
can be measured with airflow gun .........
Long vacuum tubes = vacuum drop.
what about a suitcase type genny -v quiet .......
George  ............(Delaval trained milking machine engineer)

Yes, you're on the money, a little single bucket milker with old motor and ancient alfa-laval pump

This was before i collected it


Internals were rusted and seized



Refurbed it, unfortunately two of the carbon vanes need replacing



« Last Edit: July 04, 2019, 12:41:23 PM by Greenbeast » Logged
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