Help with Car lift problem needed - Long!

OK a bit off topic , but worth a try.
A good friend is trying to start a small garage service going to service and
restore old cars.
He picked up a 2500 Kg two poster car lift from the adds and installed it.
At the same time the Electric supply company was approached and survey and
price sought to supply 3 phase to the garage to deal with the various things
he would need.
The price that came back to him was over £9,000 plus VAT. Now whilst that
may not seem a lot to some people, it is a bloody great deal when starting
and needs a lot of through put before that sort of price can be justified.
It seems there is a general problem in the area, of the transformer being
under rated for the surrounding houses and farms and the price included part
charge for new transformer of larger capacity!
So I though I would let him use my static converter 240 in 415 out at up to
4 HP
It crippled the mains when we tried to start up the 4 HP motor on the ramp
even without a car in place.
The mains input dropped to around 180 Volts to the static inverter. Larger
cable is going to be fitted to help minimise the volts drop taken from the
household supply, but the fears are that even this will not solve the issue.
I have been thinking of reducing the ramp motor from 4 HP at three phase to
2 HP and going to Single phase supply, The start-up currents would be
reduced and hopefully less chance of taking the supply down.
Now as it stands the 4 HP motor is 3 phase, runs at 1415 rpm uses pulleys to
reduce speed 70 cm and 230 cm so around 1/3 reduction in speed and the lift
screws are 5 TPI.
So my basic working out gives me 1415 * 70/230 = 430 rpm screw speed
430 rpm / 5 TPI = 86 Inch lift a minute or around 7 foot lift in a minute
which I guess is about right.
Now going down to a 2 HP motor would I need to need to reduce the lift speed
by 2 by changing the motor reduction by 6 to 1 instead of the 3 to 1 now in
use. Assuming same rpm motor.
Or would I in fact have to go even higher in reduction due to using a single
phase motor that has lower starting torque then a 3 phase 2 HP motor.
say to 7:1 reduction from the 3:1 reduction now in use.
Any advice from those in the know is very much appreciated especially from
anyone else that has done a similar change.
--
Cheers Adrian.
Reply to
Adrian Hodgson
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I find it hard to believe that a 4hp motor is enough to cripple any electricity supply unless there's something fundamentally wrong with the wiring. 4hp is 3kw which is sod all really. About the same as an immersion heater or a couple of electric fires.
I run a 3 phase mill, lathe and big bench grinder in my garage off a 5hp Transwave converter. The garage is wired as a spur from the house about 30ft away with 5mm round cable (that's 5mm o/d of the plastic sheath so the wire can't be more than 3mm I reckon). That powers 10 flourescent lights plus umpteen single phase sockets and the Transwave is plugged into one of those. I can run every machine simultaneously without any trouble at all. I'm guessing the lathe and mill are about 1.5hp to 2hp each, the motor for the power feed to the mill table maybe another 0.5 and the bench grinder about 1hp or a bit less. There's a compressor in there too (single phase) so with all the lights on and every bit of machinery running there must be about 7 or 8hp (5 to 6kw) at least. The wiring isn't an issue and the converter doesn't even break a sweat. I leave it on setting 3 out of 6 for one motor and position 4 if everything is on.
Now let's look at your lift in power terms. 1hp is 33,000 ft lbs per minute. So that would lift a 3000 lb vehicle about 11 feet in a minute. Even with 50% mechanical efficiency (which I totally doubt or the heat losses into the screws would be huge) you'd lift 5.5ft in a minute. At full weight plus say 500kg for the machine itself you're lifting 3000kg or 6,600 lbs through 7 feet in a minute. That's under 1.5hp of actual work done. A 2 to 3 hp motor ought to breeze through that. Well greased screws ought to be 90% efficient I would guess.
Your problems might be that the converter is a bit small or the start up current on the motor is very high. That could well be the case if there's no clutch and the motor goes directly from off to on and lifting straight away. Far better if the motor spins up and then lift engages once the motor's going. I know my converter doesn't like starting my lathe on very high speed until the motor is warm. I have to turn it up a notch if I want to use 900 rpm or more, especially when it's cold in there like now. As soon as the lathe motor is warm the converter starts to hum so I turn it back down a notch. I'd try a bigger converter or just fit a single phase motor to the lift. If the wiring can't cope with that then how does the guy cook his dinner?
You might try asking in rec.crafts.metalworking too as lots of the guys in there use converters and know more about them than I do.
Dave Baker - Puma Race Engines
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Reply to
Dave Baker
Adrian, I had the same problem which I solved by exchanging the 3phase motor for a 3HP single from Northern Tools (about £85) and made a reduction arrangement using a large pulley from an old drum washing machine. The car lift was the only item I have been unable to run using the original 3ph motor from single phase (plus capacitors etc). I don't know what the final reduction was but the large pulley is about 10" dia and the pulley on the motor is about 1.5" dia ,the second reduction is via the original motor pulley and the lift pulley. Its probably a bit slow but it happily lifts as it should. I hear that RS are now selling a new inverter that is reasonably priced, I think the stock number is 431-9184.
John
Reply to
John Belt
I know nothing about car ramps, but a couple of suggestions:-
Why are you planning only 2hp single phase? 3hp single phase motors are readily available, and in some situations will start/run OK via a standard 13A socket. The particular configuration of single phase motor is significant when trying to start under load - I'm no expert here, others can probably advise (eg Capacitor start/induction run, capacitor start/capacitor run etc...)
If you're trying to start a 3-phase motor under load via a converter, you stand a much better chance of success if you start up an idler motor first, preferably a bigger one than the one you want to start, though you may need to play about with the sizes of balancing capacitors if the converter is specifically for 4hp.
Bear in mind that the starting surge current for a 4hp single phase motor would be (IIRC) something over 100A, and probably won't be much different starting a 3-phase motor via a converter. This means that any significant cable runs must be sized accordingly to avoid too much voltage drop during that surge.
What about using, say, a 3hp 3-phase motor via an inverter, you could adjust the pulley sizes as you suggest, but then get back some of the speed loss by overspeeding the motor if the car isn't too heavy? I don't know what a 3hp single to 3-phase inverter would cost, but might be worth investigating, and the soft starting should ease your voltage drop problems.
Cheers Tim
I'd suggest at least a dedicated 30Amp circuit for your 4hp converter . Tim Leech Dutton Dry-Dock
Traditional & Modern canal craft repairs
Reply to
timleech
3 phase motor draws at least 2.5 times Full Load Current with a direct on line starter. current is also greater with low power factor ie 0.7 power factor requires 1.42 ties more current as voltage is out of phase with current. A wound motor is an inductor in which current leads voltage and adding a power factor correction capacitor can make a significant difference to starting current and thus cable size. The full load current will be marked on the motor nameplate. Small motors are not very efficent and losses in transmission belts gearboxes etc are very significant and screws are notoriously inefficent so any calculations need to include realistic practical allowances for each item in the drive chain. Remember these factors are multiplied not added. I have no experience of the effect of introducing 3 phase converters into the equation but a friendly competent electrical technician or engineer, given all the relevant detail, would be able to provide the answer very easily.
Reply to
Chris
A few more points Dave in no special order here.
I would not have expected the start-up to cripple the mains but it did.
Going from the household supply 240 Volts from a dedicated spur in the house with around 40 foot of armoured cable 40 amp rated, what's that about 2.5 to 3.0 mm, no idea at this end.
We used my 4 HP static converter 240 to 415 volt and measured the volts at both the spur from the meter and across the input to the converter. On trying to start up the ramp the volts dropped to 215 volts at the meter and 180 volts at the static inverter.
So two things were apparent to me, yes a large volt drop across his extension wiring but also a large drop across the mains supply. As I said there is an issue with the mains in the area, but there seems to be a reticence to upgrade the supplies to the houses by the supply company although this is being fought.
The Static converter switchable 1.5 2.5 and 4HP by Motorun of Teddington, it works well in my own garage and can drive my own mill quite happily. My own mill is 2HP and is very quickly up to speed, the difference is here that the lift is starting up under load which is not the case with a mill or a lathe.
The motor on the lift at 415 Volts 3 phase is 3.45 KW so OK just over the 4HP but it is probably 4HP output and takes a bit more from the supply. I think it was 4.8 amps per phase on the plate.
If the static converter was 100% efficient then I would see 13.8 Amps drawn from the 240 volt mains supply, expect around 70% so would draw around 20 Amps from 240 Volts single phase. The issue is in trying to start the motor.
When used in my own Garage on the 2 HP mill the converter draws 10 amps, it takes 30 amps surge on start possibly a bit higher but the meter I use is not fast enough. In it works in the same ratio then I would see in excess of 60 amps start-up surge on the 4 HP motor, and the volts drop that happens at this point is enough to drop the voltage so the converter has no chance.
From my college work a screw lift is somewhere around 40% efficient which is crap to say the least, but they are safe. The issue must be in the start-up current through the converter as the motor is trying to drive the lift at start-up.
Back to the main point of why I am asking about a single phase 240 volt 2 HP motor, it would reduce the start up current and running current, have no losses due to a 240 to 415 volt converter.
Just that as before the motor would have to drive the lift under load from start up, and HP may not be an issue but torque may be.
Gas is the answer to the cooking problem with Oil Central heating etc.
Reply to
Adrian Hodgson
Thanks John;
So it must be do able then as you have done it, is the single phase motor you use a cap start and cap run, I believe they are the best for starting under load. Your reduction seems to be around 6.6:1 plus the original belt reduction, in this case that would be just over a ft per minute lift is that what you have.
-- Cheers Adrian.
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Reply to
Adrian Hodgson
2.5 x full load current 4.8 Amps I think it was, is 12 Amps, is that per phase. If so then the input at 415 would be 415 x 12 x (root 3) comes to around 8.6 Kw, translate that to a 240 volt circuit and this gives around 36 Amps, add to this losses in the converter and it is no wonder the mains dips as it does. I think a screw thread is around 40% could be worse not sure.
Thanks for the advice/help, I might even suggest he buys a 3 phase generator and runs that when required. -- Cheers Adrian.
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Reply to
Adrian Hodgson
Good idea on the meter, I have an a.c. clamp meter thinking about it, that will save the max value, now why did I not use that dam thing when trying to get the lift running.
I think that Cap start motors are more suited to starting under a load rather then the induction coil ones, possibly for the reason you mentioned.
Thinks for the memory jogger on the meter Chris, much needed to tell me exactly what is going on.
-- Cheers Adrian.
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Reply to
Adrian Hodgson
Adrian
First problem - you have the wrong type of ramp (not a lot of help I know). In single phase locations the one to go for is a hydraulic - either the traditional four post or a newer two post. Bradbury have made these in single phase for many years the only difference to the three phase being a smaller motor which does slow down operation somewhat. The softer start associated with the pump presumably lends this type better to single phase useage. You don't say what make / model of ramp you have, if you post the details I will try to get you more info. I have a client who is a main Toyota dealer who runs the whole workshop on single phase, he has four hydraulic ramps with single phase motors and two three phase tecalamit screw ramps running on a converter using a constantly running ballast motor which looks to be about 3 HP. I have never seen a single phase screw ramp and assume this is due to the high starting currents generated by the high mechanical resistance of the screws and drive chain (I assume yours is a single motor model). I would think that your best solution would be to introduce a lay shaft and subsequent gear reduction between the motor and screw shaft, the result will be a much slower lift but this won't be a problem in a small workshop. Alternatively can you make some sort of clutch arrangement between the motor and screw so you can start the motor before applying the load? You need to check the lifing nut wear on these ramps on a regular basis - if you post details of the model I will let you know how to check them.
Gaspode
Reply to
gaspode
Ramp is not mine but have been back to friends garage this morning and believe it was a Bradbury, It has a single motor with a 3 belted pulley on top of one shaft gears and chain as you suggested at the bottom of the screw's to the second ramp. I have been told this morning that there was a mod kit years ago that included motor and gearbox to take it to 240 Volts single phase but costs approached that of a modern ramp.
Just measured the starting current at 50 plus Amps, that fact that the mains is dropping to 180 Volts at the starter means it could be higher current.
The main issue is cable size, I think to the garage for this level of current. So the friend is going to up grade to 6 mm csa. run is about 22 metres.
I think after that the best way will be to go for a single phase motor and lay-shaft as you suggest, this has been done by another poster.
OK on the hydraulic style of ramp, I can see would be a benefit, but things are down to cost while the business starts up and the ramps are second hand and in very good mechanical condition. I will be looking out on ebay for any 2 HP motors with 90 degree gearboxes I think.
-- Cheers Adrian.
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Reply to
Adrian Hodgson
I'm normally a strong supporter of simple capacitor static phase converters but not when large starting torque is needed. Capacitor values can be tweaked to give acceptable 3 phase balance between light load and full load but it is impossible for this type of converter to deliver balanced 3 phase into a stalled rotor at startup. To achieve both correct phase angle and phase voltage at start up, the capacitor needs to be fed from a voltage higher than the supply voltage and this is not normally available. With typical static conversion you will be lucky to achieve even half the normal 3 phase peak starting torque.
A large capacitor start single phase motor could solve your problem but, even so, it's a pretty unkind load for a single phase motor and you would need to be careful that frequent starts did not overheat the starting winding.
A simpler and probably cheaper alternative is to add an idler motor preferably as large or larger than the lift motor. Once this motor is up and running it can supply much larger balanced starting power than the parent static converter.
You can get a pretty good idea of whether this is feasible by simply mechanically disconnecting the lift motor which should then start quite happily at no load from your existing converter. Peak starting currents will still be quite high so the voltage drop on your long 240v supply lead will still be significant so it would be better site the converter at the 240v supply end and run 415v thru the long lead.
I'm not sure where your 2HP mill is located but if it is reasonably close you could use this as a temporary idler - it's a bit small but should be man enough to start the lift on fairly light load and give you a good idea of the size of idler motor needed. Large 3phase motors are readily available from scrap dealers. The idling motor puts little dissipative load on the static converter and this can be left at its 4hp setting running the idler motor ready to supply the lift motor when needed. Hope this helps
jim
Reply to
pentagrid
Hi Jim; we did try to use an idler motor, only a 3HP one granted, that is the normal situation I use at home on my own 2 HP mill.
So the whole lot was taken with us to the new "Garage" and tried, Idle motor started first no problem then put the 4 HP motor across the output and it stopped the idle motor in its tracks.
We are loosing to many volts across the feed cable at 240 Volts and this will be changed to 6 mm soon.
Another poster has successfully fitted a 2 HP single phase motor and put in an idle shaft to give further reduction. I think that something along these lines will end up being the final solution in the longer term even if the static converter manages to cope.
I have even considered the idea of a hydraulic pump and motor running the pump from a single phase motor and then using a hydraulic motor to turn the screws, but suspect costs of these units are not cheap to obtain.
-- Cheers Adrian.
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Reply to
Adrian Hodgson
Any way to try out a 3-phase inverter (variable frequency drive) up to running this motor? If it can soft start the motor, that might be all that's needed.
- Brian
Reply to
Brian Drummond
This is an ideal application for a single to 3 phase invertor. With a fairly slow start up ramp to control the startup current and a maximum output of (maybe) 25Hz or whatever is possible given the limitations of available current. It will end up costing less than a new motor and modifications.
my 0/2d worth
Mark Rand RTFM
Reply to
Mark Rand
springs to mind is that useing a single phase motor to run the lift may hold the starting coil on for a long period of time as it accelerates to normal RPM. This could lead to overheating and failure of the coil. I have had a similar problem with a fractional HP motor starting a lathe (using a 1/4hp motor as this was available when 3/4hp was the correct rating.). If possible wire in an ammeter and monitor the current draw when trying your idea out.
Chris.
Reply to
Chris Welbourn
Adrian
Just a note of warning, most of the older Bradbury 2 post screw ramps are VERY susceptible to lifting nut wear and you need to check this carefully and regularly. If your ramp has the sheet metal covers at the rear of the posts secured by four push & twist fasteners then you have one of those which wear quickly. You should see two square bronze nuts seperated by about 25 - 30mm when the covers are removed. The original gap between these nuts is often marked on the top nut and you need to renew them if this measurement decreases by 1.5mm. Beware though, the original dimension marked on the nut is not always accurate! Best to lever the nuts apart and measure max and min. dimensions then use 1.5mm difference as a renewal criteria. The good news is that excess wear on these nuts is nearly always caused by lack of lubrication and a few shots of grease into the top nut once a week will ensure that you don't need to renew them frequently, (cut a 50mm hole in the sheet metal covers so you can get a grease gun in without removing them). Also ensure that the safety cable (3mm wire rope passing from one set of nuts to the other) is in good nick and properly adjusted.
Gaspode
Reply to
gaspode
Adrian,
Going on from what Gaspode has just said - is it at all possible that a set of new lift nuts might solve all your difficulties?
Mike
Reply to
Mike Whittome
Brian;
Thanks for the advice
I don't have any Inverters at 4 HP to try unfortunately.. It would also mean a change to the contactor in the control box, no big deal really. must admit to not seeing any 240 Volt input 4 HP Inverters, I thought they stopped at 3 HP or 2.2Kw. Going off the performance of my on 2.2 KW Inverter used on my Herbert lathe I would have doubts if the inverter would start the motor if the motor was under full load at start-up, even with the units boost allowance. The ramp need to be able to start with a car on it unlike the normal situation we use on a mill or lathe were we start, run to speed, and then apply the cut.
I am willing to be convinced if anyone has a spare 240 Volt 4 HP inverter?
-- Cheers Adrian.
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Reply to
Adrian Hodgson
Your information is now printed out and will be handed over to Andy the guy with the garage.
Words of warning regards equipment are always appreciated.
-- Cheers Adrian.
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Reply to
Adrian Hodgson

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