Need a lot of help from you good people

[wendy jacksonParticipant @wendyjackson]

Hi. Thanks for all the physics. I have a question. Would fitting a motor from an electric bike and a 48v 15ah battery with new controller work. These motors come in 350w 500w and 1000w. But getting information on the torque they produce is hard to get. Surely there must be an answer to this.

[Robert Atkinson 2Participant @robertatkinson2]

If you know the power and RPM you can calculate the torque. I think a bike motor may run a bit fast and need a bit of reduction gearing. Be aware that their ratings can be optimistic and they may not be capable of the short term acceleration overloads the old ones could take.

A typical ebay "500W 24V DC 26.7A Electric Motor MY1020 + bracket for E-Scooter Electric Bike Is 640W in put power and 500W Max (continuous or 1min?) at 2500 RPM so torque is 1.91Nm or 1.41 lbf.ft

Robert G8RPI.

[SillyOldDufferModerator @sillyoldduffer]

Posted by terry callaghan on 20/08/2019 11:21:00:

Hi. Thanks for all the physics. I have a question. Would fitting a motor from an electric bike and a 48v 15ah battery with new controller work. These motors come in 350w 500w and 1000w. But getting information on the torque they produce is hard to get. Surely there must be an answer to this.

An electric bike motor and controller would certainly work. The power needed is decided as per earlier physics by:

• the need to overcome friction in the bearings, drive train and motion work (in good condition). This can be gauged by pushing the engine by hand. A man working steadily can deliver about 250W, up to say 500W in ten minute bursts, and Olympic athlete up to 1500W for a few minutes. If the engine is easy to move 350W should drive it, otherwise 500W. If it's very stiff, check the bearings etc.
• How fast the train needs to accelerate in service. A 100W motor can do the same amount of work as a 500W motor, but it needs 5 times longer to do it. That might be too time-wasting for comfort! If it wasn't for friction, a 1W motor and gearbox could move your engine, but it would be incredibly slow. You're looking for a reasonable balance between power and performance. Having plenty of power is exhilarating, but it's not necessary on a track model. Steam engines don't accelerate quickly in full-size and an electric model pulling wheelies down the track might not be popular!
• Any hills the engine needs to climb. Once it's moving, pulling a train around a flat track doesn't do much work, but going up hill does! As railways are built flat, I think in practice this would just limit the weight of carriages and passengers that could be pulled at a particular site. This is echoed in full-size practice: railway freight engines are sized powerful enough to restart their load in the event the train is forced to stop on the journey's steepest incline. Engines for passenger trains are sized to accelerate to meet the timetable.

Other issue that might suggest a big motor is whether or not the engine is to be run continuously. A 350W motor run flat-out for hours will have a shorter life than a 1000W motor run at 350W simply because the big motor stays cooler. So motor size matters less on an engine run intermittently for fun at the track by the driver and a few bystanders than the same engine expected to haul hundreds of paying passengers continuously over a Bank Holiday weekend event.

A 15Ah battery can deliver 15 amps for an hour. That's 48V*15A = 750W for an hour. Actually, because deep discharging is undesirable, it would be unwise to assume more than about 75% of that, say 750W for 45 minutes, which isn't unreasonable for fun use. A 350W motor would use half the power and run for about 90 minutes, 500W about an hour. In practice because the motor probably wouldn't be run at full power all the time, it would likely last longer per session. But so much depends on stops, starts, how hard the driver accelerates, the rolling resistance of stock, slopes and the state of the track it's hard to predict.

I bet the original builder would have used a modern electric bike motor and batteries if they'd been available at the time.

Dave

Edited By SillyOldDuffer on 20/08/2019 14:21:55

[Ron LadenParticipant @ronladen17547]

The maths and calculations dont interest me that much to be honest I would rather go with what works in practice and a sprinkling of gut feeling. The loco in this thread is obviously quite a lump add to this a couple of riding cars and 10-12 passengers and for me 500 watts is not enough, yes it will run but I think it will be a bit gutless and it would certainly struggle with any inclines. If it were mine I wouldnt put less than a 1000 watts (1 1/4 HP) in it and I dont believe that is too much nor do I think that 2 HP is seriously over powered as was suggested.

Of course if it is to be run with just a single car, a driver and a couple of passengers then less power is possible but with it being 7 1/4 inch I imagine it running on a track were good numbers of passengers are carried.

[wendy jacksonParticipant @wendyjackson]

Hi Ron, I have know interest in pulling people around and the club I am a member of doesn’t do public running. Fitting a 1000w motor in place is not an issue. However the battery’s are. At the moment I am thinking 500w motor but still stuck with what battery or battery’s to use.

[Ron LadenParticipant @ronladen17547]

Thats fine then Terry go with what you feel will be about right for your type of running.

[Tim StevensParticipant @timstevens64731]

SoD says (above) – A 15 Ah battery can deliver 15 Amps for an hour.

Sorry, but this is based on a misunderstanding. It is true that a 15 Ah battery willl (should) deliver 1 Amp for 15 hours, but that is not the same thing. 15 Amps would overload a small battery, causing overheating, and likely damage to the plates, if continued more than a few minutes.

It is just one of life's (many) swindles, sorry.

Cheers, Tim

[Dave HalfordParticipant @davehalford22513]

There's what looks like old perished rubber cabling mixed with PVC, no idea what all the OTT twisted together wire is for. The engine may have been part way through a rebuild. There's a lot of reliance on airgaps for insulation.

I would take a motor off and look for the motor plate for the voltage, give the comm a shine with wet and dry and then try bench running it. There are so many Heath Robinson bodges on view and a full short across a 100A battery might be more exciting than you bargain for.

[wendy jacksonParticipant @wendyjackson]

Thanks Dave.i have removed both motors but there is nothing on them. I think it’s time for both of them to hit the bin. So far I am looking at a 500w motor to run the loco. My problem now is what battery’s to use. If I go for leisure battery’s I will be adding a ton of weight. If I go for more modern battery’s it’s a mine field. But if I am to keep it,I know I need to keep it simple. So chaps the question is what battery to run a 500w motor for say 3/4 of an hour. With one maybe two adults. Thanks.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Tim Stevens on 20/08/2019 18:01:10:

SoD says (above) – A 15 Ah battery can deliver 15 Amps for an hour.

Sorry, but this is based on a misunderstanding. It is true that a 15 Ah battery willl (should) deliver 1 Amp for 15 hours, but that is not the same thing. 15 Amps would overload a small battery, causing overheating, and likely damage to the plates, if continued more than a few minutes.

It is just one of life's (many) swindles, sorry.

Cheers, Tim

Not quite, Terry mentioned using an ebilke battery. They're Lithium Ion high current batteries capable of delivering quite a wallop. This ebay example claims to be good up to 1200W.

Dave

[Dave HalfordParticipant @davehalford22513]

Posted by terry callaghan on 20/08/2019 18:45:35:

. My problem now is what battery’s to use. If I go for leisure battery’s I will be adding a ton of weight. If I go for more modern battery’s it’s a mine field. But if I am to keep it,I know I need to keep it simple. So chaps the question is what battery to run a 500w motor for say 3/4 of an hour. With one maybe two adults. Thanks.

That depends if you need the weight on the wheels for traction or not

[not done it yetParticipant @notdoneityet]

Posted by Tim Stevens on 20/08/2019 18:01:10:

SoD says (above) – A 15 Ah battery can deliver 15 Amps for an hour.

Sorry, but this is based on a misunderstanding. It is true that a 15 Ah battery willl (should) deliver 1 Amp for 15 hours, but that is not the same thing. 15 Amps would overload a small battery, causing overheating, and likely damage to the plates, if continued more than a few minutes.

It is just one of life's (many) swindles, sorry.

Cheers, Tim

Spot on regarding the hype. They should give a capacity at a particular discharge rate (and probably a final voltage, too).

Usual is C/20 discharge rate. Rate over 20 hours. Faster discharge means rather less capacity. Fully discharging also shortens the life of the battery. Lead acid technology needs careful attention for good battery life.

But, of course, Lithium ion batteries also require careful nursing to get the maximum from them. Battery management systems on electric cars is a must – then they will last years with heavy charge and discharge cycles. Your average cell phone or tablet battery won’t last as long for several reasons. Different chemistry, full charge/discharge cycles, and ‘china’ factors all help to destroy them in a relatively short time.

[Ron LadenParticipant @ronladen17547]

Posted by terry callaghan on 20/08/2019 18:45:35:

So chaps the question is what battery to run a 500w motor for say 3/4 of an hour. With one maybe two adults. Thanks.

Terry, what voltage is the 500 watt motor you are considering..?

[wendy jacksonParticipant @wendyjackson]

500w 36volts.

[Robert Atkinson 2Participant @robertatkinson2]

Allowing for losses and being conservative, three 18H 12V batteries would do assuming full load all the time. If you are optimistic then three 12AH would do.

However as noted above running a battery at it's 1H rate or faster is not good for it, Ii'd go for a bigger battery if you have space.

Three of these would be OK (I've never used this seller or brand) https://www.batterymegastore.co.uk/catalog/product/view/id/6518/s/victron-energy-bat212200084/category/363/

Robert G8RPI.

[wendy jacksonParticipant @wendyjackson]

Hi Robert, thanks. Just ordered three batteries, new control unit from 4QD and a 500w motor. So will see if it all works, when it turns up. Should be interesting. Michael

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