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Gearing and load capacity for a battery electric loco

Zokko!

Joined: 4-01-12

Topics: 1

Replies: 6

Posted: Mon 16th Jan 2012, 11:12pm
Gearing and load capacity for a battery electric loco

I have recently joined the 7 1/4 society and have also just bought a second hand battery electric loco which I hope to use for serious passenger hauling at the club track. On trial yesterday the loco seems to be geared too low as it was running at between 4 and 6 mph (measured by gps) depending on gradient. It has two Bosch 1 hp motors running at 24v, and I believe the batteries to have been fully charged. My question really is what should the hauling capacity be for this loco, and what top speed should it be geared for? I think the club normally runs passenger trains at around 8-10 mph, so this loco currently would create delays. It is an 0-4-0, fairly heavily (and soundly) built, and has two stage reduction by chain drive. It would be fairly simple to increase the size of the motor sprockets to up the gearing. I was hoping that a load of 8 or more adults would be within its ability, given the relatively gentle gradients expected. Obviously raising the gearing will lower the maximum load, so I am looking for a compromise. I haven't yet had a chance to work out what reduction it has so I suppose I am looking for suggestions of the ideal, and will then compare these with what I actually have.

Chris
 

Replies To This Post

Peter Beevers

Joined: 9-10-01

Topics: 3

Replies: 134

Posted: Tue 17th Jan 2012, 7:35am

Chris,

I'm no expert on electric locos, but Parkside Railways old website said that 1HP should be able to manage 1 ton on the level at 10mph. Gradients and curves significantly reduce this. On average, an 8' loaded vehicle will weigh just over 1/2 ton.
Parkside are rebuilding their website, so that (very helpful) info isn't there at present, but they have added a gear ratio calculator: http://www.parksiderailways.co.uk/gear_ratio_6.html

Hope this helps,

Peter
 

Zokko!

Joined: 4-01-12

Topics: 1

Replies: 6

Posted: Tue 17th Jan 2012, 10:07pm

Peter

Thanks for your comments. I had noticed that some of my old bookmarks for the Parkside website were no longer working! I'm OK about working out gear ratios but what I really need to know is what top speed to aim at in order to run at around 8 mph whilst still having reasonable pulling capacity. Also if anyone else has experience of a similarly powered loco, what load can it pull? Is the Parkside rule of thumb accurate in practice?

Chris
 

Peter Beevers

Joined: 9-10-01

Topics: 3

Replies: 134

Posted: Wed 18th Jan 2012, 8:13am

Chris,

The Parkside rule of thumb is just that. The variables are far too many to be able to be more specific - rail head condition, track gauge, gradient, curvature, gauge widening all contribute to robbing you of hard-earned pulling power. My suggestion is that, to balance at 8mph, you should aim for a maximum of 10-12mph.
A 2hp electric loco is a BIG beast - you will need LOTS of weight in there to keep the wheels stuck to the rails.

Peter
 

ivanhewlett

Joined: 1-01-85

Topics: 8

Replies: 53

Posted: Wed 18th Jan 2012, 2:30pm

Hi

I have built a locomotive using Parkside motors (3000 rpm type) and a design speed of 8.1 mph and find it works fine.
In fact the theory of gear ratios and the practicalities of miniature locomotive design, at least in 71/4" gauge, coincide quite nicely.
I used the smaller 8mm metric chain from Parkside and used the smallest sprocket available for the motor. Then I fitted the largest possible sprocket on the axle (decided by ensuring a gap over the railhead of approx 5mm to the outside of the chain over the sprocket) and this gave me 8.1 mph.
Point is it doesn't matter what size wheel you use if you go for the largest possible sprocket you will always get approx 8 mph top speed !! This is simply because your wheel tread is then effectively running at (almost) the same surface speed as the pitch circle diameter of the small sprocket.

This gives workable torque, over a good speed range and enables a single reduction to be used with chain drive.

I prefer chain over delrin gear dives because of the likely damage to the delicate teeth on the driven gear in derailment conditions. I have spoken to people who say it's 50:50 whether the gears survive, simply depending on which way the wheelset jumps.

At 8 mph I have never been told that I am running too slowly, but on occasion have been asked to slow down - particularly if passenger hauling, 10 mph seems a bit fast to me !?!?

I have no links with Parkside except as a very satisfied customer.

Cheers, Ivan
 

brianhicks

Joined: 5-05-01

Topics: 4

Replies: 12

Posted: Wed 18th Jan 2012, 5:00pm

As the owner of a large Tinkerbell and being a non-engineer I can add nothing to the original enquiry except to join the query about a suitable speed when pulling passengers. This may well cause more to join in,but in my experience of passenger hauling the higher speeds quoted seem to me rather too fast. I would only consider a top speed of no more than 6mphto be more than adequate.After all passengers like a longer ride. More views I am sure will be forthcoming!!
 

Zokko!

Joined: 4-01-12

Topics: 1

Replies: 6

Posted: Wed 18th Jan 2012, 6:50pm

Some interesting comments, thanks. On the only day I have run my loco so far there was just one other train on the club track, carrying passengers. This was hauled by a Tinkerbell and I was mildly chastised for causing it to slow down on one circuit. On other days there will be several trains operating so I won't be able to always set off from the station (there are two roads in the station) at a time to avoid being "in the way". This is why I need to run a little faster.

Chris
 

ivanhewlett

Joined: 1-01-85

Topics: 8

Replies: 53

Posted: Wed 18th Jan 2012, 8:41pm

Hi Again
I think that Brian and I share similar views and I would hope that any, even mild, chastisement for running 'too slowly' were only meant in jest.
Speed has never been an aim of mine in running my locomotives - in fact I have tried my damndest to get my GWR Railcar running more slowly - (when it runs at all ;-) )
I really think that top speed gearing of 8 mph is the way to go, as this will give adequate torque at the more usual lower running speeds. I ran the F7 both at Leyland and Echills AGM's and unless anyone knows differently I don't think I caused any problems ?

Cheers, Ivan.
 

colinedmondson

Joined: 9-08-09

Topics: 3

Replies: 82

Posted: Thu 19th Jan 2012, 9:43am

We have a loco at High Legh which has one Bosch motor, with parkside controller, very well geared down. It cannot exceed 5 mph, but will pull and pull until the wheels slip. Altering the gearing would give us more speed at the expense of torque for load pulling, swings and roundabouts. I think that top speed has to be down to a personal or engineers assessment of what is safe. A well laid club track with 120' curves and gentle transition curves may well be suitable for well in excess of 10 mph, a more lightly laid track with 40' curves and no transition may be unsafe at any speed over 5 mph. Standard gauge profile with its much lower centre of gravity is safer at speed than my loco, which is a half scale 2' gauge, rather tall and a lot chunky! It is geared for 5mph flat out, and with 5 hp pulls well, even with only a single speed drive. On a local club track a petrol electric standard gauge outline loco on well sprung 6 wheel bogies regularly tops 15 mph in complete safety, but the speed alters the hair style somewhat. It may be possible to build an electric loco with two sets of sprockets, simply moving the chain according to which track the loco is going to run on. Ivan, I hope that you persevere with the railcar, it has inspired me to go petrol electric. Cheers, Colin
We have a loco at High Legh which has one Bosch motor, with parkside controller, very well geared down. It cannot exceed 5 mph, but will pull and pull until the wheels slip. Altering the gearing would give us more speed at the expense of torque for load pulling, swings and roundabouts. I think that top speed has to be down to a personal or engineers assessment of what is safe. A well laid club track with 120' curves and gentle transition curves may well be suitable for well in excess of 10 mph, a more lightly laid track with 40' curves and no transition may be unsafe at any speed over 5 mph. Standard gauge profile with its much lower centre of gravity is safer at speed than my loco, which is a half scale 2' gauge, rather tall and a lot chunky! It is geared for 5mph flat out, and with 5 hp pulls well, even with only a single speed drive. On a local club track a petrol electric standard gauge outline loco on well sprung 6 wheel bogies regularly tops 15 mph in complete safety, but the speed alters the hair style somewhat. It may be possible to build an electric loco with two sets of sprockets, simply moving the chain according to which track the loco is going to run on. Ivan, I hope that you persevere with the railcar, it has inspired me to go petrol electric. Cheers, Colin
 

ivanhewlett

Joined: 1-01-85

Topics: 8

Replies: 53

Posted: Fri 20th Jan 2012, 10:57am

Hi Again
Good thoughts from Colin, and yes two speed gearing is certainly an option. My F7 has a total of 2Kw of motors ( around 2.5HP) and pulling power is more than adequate for my needs.
I am glad that despite the problems my railcar has in some way inspired you, that is the fun of electric transmission - it is so easy to experiment with. In fact I am rethinking the railcar and how to improve reliability - using bits an pieces I have collected over the years. In fact I have one quite radical idea, so watch this space.
To Zokko though I would say just talk to people and find out how they have got on, there is a lot of knowledge out there.

Cheers, Ivan.
 

Keithf7

Joined: 1-01-97

Topics: 0

Replies: 19

Posted: Sat 21st Jan 2012, 10:19am

I would like to add my tuppenceworth concerning the Bosch motor. The no load speed is 3300rpm and in my experience it does not like labouring at low speeds. Ivan's advice of a small sprocket on the motor and a large one on the axle is crucial to getting the motor to work efficiently.
Cheers,
Keith.
 

Zokko!

Joined: 4-01-12

Topics: 1

Replies: 6

Posted: Sat 21st Jan 2012, 3:38pm

I have now had a chance to get the bonnet off the loco in daylight to check what sprocket sizes etc are installed. As far as I can tell, allowing for working in less than perfect circumstances since I can't yet get the loco into my workshop, the motor sprockets are 12T driving 40T on the layshaft. Then 12T on the layshaft driving 40T on the axles. The wheel diameter is 8.25 inches as close as I could measure it. By my calculations this gives a top speed of 7.29 mph using 3300 rpm at the motors. I should be running again tomorrow so I will see whether it can reach this speed then. I should add that one of the drive chains, from motor to layshaft, was exceedingly tight and I have now adjusted it to be a fair bit slacker. Advice received at the club is that this tight chain would have absorbed a lot of power, so maybe that explains the low speeds experienced on the first outing.

Assuming it can now maintain 7 mph around the track I may consider increasing the motor sprocket size to 14T which should give around 8.5 mph top speed, without reducing hauling capacity too much I hope.

Thanks for all your helpful comments.

Chris
 

Zokko!

Joined: 4-01-12

Topics: 1

Replies: 6

Posted: Sun 22nd Jan 2012, 9:14pm

The loco ran much better today, over 7 mph at several places and averaging over 5 mph for the whole circuit with 3 people. With a moderate load of 6 people on 2 trucks speed fell to about 4.5 mph at the toughest part of the track, but picked up on the down grades so that the overall average was about the same. Later train loads of up to 12 passengers were not so successful, with the loco down to a crawl at times. I'm not convinced that all is well with the drive; perhaps one of the motors is not pulling its weight or there may be too much friction somewhere since the loco is quite hard to push along. I am fairly happy about the gearing though, which seems to allow a reasonable turn of speed when required. I also need to check that the batteries are up to scratch since I have little knowledge of their history. It's all good fun and I'm enjoying the steep learning curve.

Chris
The loco ran much better today, over 7 mph at several places and averaging over 5 mph for the whole circuit with 3 people. With a moderate load of 6 people on 2 trucks speed fell to about 4.5 mph at the toughest part of the track, but picked up on the down grades so that the overall average was about the same. Later train loads of up to 12 passengers were not so successful, with the loco down to a crawl at times. I'm not convinced that all is well with the drive; perhaps one of the motors is not pulling its weight or there may be too much friction somewhere since the loco is quite hard to push along. I am fairly happy about the gearing though, which seems to allow a reasonable turn of speed when required. I also need to check that the batteries are up to scratch since I have little knowledge of their history. It's all good fun and I'm enjoying the steep learning curve.

Chris
 

craiggluyas

Joined: 1-01-70

Topics: 0

Replies: 10

Posted: Mon 23rd Jan 2012, 9:35am

Sounds almost certainly like the batteries are shot! Two bosch motors should be able to handle 4 coaches really, especially if geared to 7MPH. I've driven several locos fitted with just one and they have handles 2 x 8' coaches with ease when geared to 8mph. If you want to check the gearing, and I'm assuming the loco has a speedo from the previous posts, simple jack it up off the rails and turn it on! We did this with a loco which was labouring on the ground and found that it was actually geared to 12mph!

I thought the no load speed of the Bosch was 4200RPM though?

Craig
 

Zokko!

Joined: 4-01-12

Topics: 1

Replies: 6

Posted: Mon 23rd Jan 2012, 6:47pm

Craig

KeithF7 quoted 3300 rpm above, and though I have struggled to find detailed specs of this motor on the web this web page: http://showcase.designnews.com/content/bosch-gpa-motor also quotes 3300 rpm. If my motors should really be rated at 4200 rpm then that would mean I am geared for over 9 mph, whereas the measured top speed has been not much over 7. The speeds referred to in my earlier posts were all measured using a wrist mounted gps which I also use when running and cycling. The loco does indeed have a speedo fitted but this tends to fluctuate in its reading unless the track is very smooth, so it is hard to get sensible data from it. I suppose it might give a steady reading with the wheels jacked up.

I am fortunate to have been offered to swap my batteries (temporarily!) with a set of known performance to allow a comparison to be made. I am also hoping that my set will improve in performance by being used and charged regularly, which is something that they have not had the benefit of with the previous owner.

I'm sure I'll get to the bottom of this question before too long, after which I should have a strong puller for regular passenger hauling. Thanks to everyone for your contributions.

Chris
 

BobL

Joined: 1-01-70

Topics: 1

Replies: 7

Posted: Sun 29th Jan 2012, 8:47pm

At the Bristol society (BSMEE) we have built Thomas Telford based on a Class 67 design.  We use a Honda engine  driving an alternator with 2 x 12volt batteries.  The output is fed via a 4QD controller to two 1500watt Parkside bogies (2 x 750 watt motors per bogie).  
Top speed, which is function of the no load speed of the motors, is around 10mph but we red line the speedo at 8mph as we consider that quite fast enough for passenger hauling.    The advantage of using an alternator is that you do not have to charge the batteries at the end of the day and you get much better performance as the alternator voltage regulator automatically maintains around 28volts even under heavy load.   
We  can pull seven coaches with  50 people and the limiting factor is wheel adhesions, it does need careful driving when fully loaded.  With  a more normal load of 20 people it just romps round.  Be pleased to supply more details if required.  See ME Vol205 No 4391 Nov 2010 for a description.
At the Bristol society (BSMEE) we have built Thomas Telford based on a Class 67 design. We use a Honda engine driving an alternator with 2 x 12volt batteries. The output is fed via a 4QD controller to two 1500watt Parkside bogies (2 x 750 watt motors per bogie).
Top speed, which is function of the no load speed of the motors, is around 10mph but we red line the speedo at 8mph as we consider that quite fast enough for passenger hauling. The advantage of using an alternator is that you do not have to charge the batteries at the end of the day and you get much better performance as the alternator voltage regulator automatically maintains around 28volts even under heavy load.
We can pull seven coaches with 50 people and the limiting factor is wheel adhesions, it does need careful driving when fully loaded. With a more normal load of 20 people it just romps round. Be pleased to supply more details if required. See ME Vol205 No 4391 Nov 2010 for a description.
 

Zokko!

Joined: 4-01-12

Topics: 1

Replies: 6

Posted: Mon 30th Jan 2012, 9:32pm

Obviously a very powerful beast. I would be interested to know the horsepower of the Honda engine and the rated output of the alternator. Before buying my BE loco I researched building either a petrol (or diesel) driving by hydrostat or using an alternator and traction motor(s). I also considered battery electric. I came down in favour of a diesel engine driving an alternator with speed control by varying the alternator field voltage. Lack of time has meant that I have gone for the easy option and now have the BE loco described earlier in this thread, though I still seek the best performance in terms of the load it can haul. I am wondering therefore about the possibility of using an existing petrol generator to provide extra power on the move. Probably not a good idea since it has 240v ac or 12v dc outputs only. Maybe I could squeeze in a small petrol engine and alternator under the bonnet of the loco, enough to at the very least extend range? 100 amp alternators are not uncommon, and ought to provide sufficient power to run my 1500w loco with ease. (60 amp should be enough most of the time). Better to run the power through batteries, as in your loco, or direct to the motors? Can your loco run for a time without the Honda, just on battery power, or is that something you never do?

Chris
 

ivanhewlett

Joined: 1-01-85

Topics: 8

Replies: 53

Posted: Tue 31st Jan 2012, 9:28am

Hi Again
Well Zokko and Bobl, you both seem to be thinking along the same lines as myself. My Santa Fe F7 is basically the same type as Bob's Class 67 in as much as it uses an engine/alternator assembly with, in my case 2KW of traction motors.
Actually I would recommend any BE locomotive owner to consider adding an alternator system to their locomotive. Connecting an alternator to an engine could not be easier and the beauty is that all the 'complex' control gear is already built in to the standard alternator. In my case I simply have a solenoid actuating the Honda engine throttle in a binary, idle or full revs, mode. The Honda engine has a built in governor that controls output speed regardless of load. The two work well together and the manufacturers of both engine and alternator have done all the hard work for you. There are only three connections to be made, Gnd, output and charging light.
The basic rule of 750 Watts equals 1HP is worth remembering.
In the case of the Class 67 this means that the output HP is around 4HP. So if you use a 5HP Honda and achieve 80% efficiency through the alternator that'll be fine. At 24 volts that will require a current of upwards of 90 Amps - so a biggish alternator is needed !!
You should always have batteries in circuit for the alternator to regulate against and in my case I have been happy to run for several hours on batteries alone. Once back home I leave the batteries connected to a 3 stage mobility scooter charger to keep them fully charged while out of use.
The engine/alternator assembly could be built into a tender or box van and simple connections can be used to the locomotive. Voila, suddenly your BE is a Hybrid with extended running time and higher available power - and to be honest a Honda 5HP and alternator can probably be bought for about the same price as a decent set of batteries.

Just a thought.....

Cheers, Ivan.
 

BobL

Joined: 1-01-70

Topics: 1

Replies: 7

Posted: Wed 1st Feb 2012, 10:27am

My comments on Thomas Telford seem to have sparked a chord.

As Ivan says introducing a petrol engine and alternator with internal voltage regulator is not difficult, provides much better performance and you do not have to provide any external charge to the batteries, it will keep running as long as you have fuel in the tank. I like the idea of putting it in a separate wagon.

Telford has a 5 1/2hp Honda engine driving an 80A rated alternator. Vehicle alternators are less than 50% efficient and their current rating is for 9,600 rev/min. With a 2/1 ratio we run the alternator at 4,300, which gives a maximum current of some 40A. 1 1/2hp out with 3hp in, well within the design limit of engine and alternator. This provides plenty of power to pull the heaviest load with wheel slip limiting the power that can be used. For reliability the design aim was to run everything at no more than half rating, including the motors.

Yes Chris we do run on battery only and have a position on the ignition switch for this purpose. Performance is in this mode is adequate but there is much more power available when using the alternator as, unlike the battery volts which drop when load is applied, the alternator regulator maintains full 28 volts up to 40A.

Regarding using direct control of the field of the generator you must bear in mind you will have to have a much bigger generator to supply the full starting current of the motors, which in our case is over 200A. The 4QD acts as a transformer and give a high secondary current at low volts to the motors, with a high voltage and low current on the input. It also provides a current limit, which is useful in case of stalling. Also there is no danger of overvoltage, which could take out the diodes. To me batteries and a controller seems the best way to go.

Not sure about the cost of a generator being less than batteries. As the batteries in Telford are floating with no deep discharge we use normal commercial vehicle batteries.

If you can, get hold of the ME, which gives a full description of Thomas Telford and I have recently written a follow on article (not yet published) describing our experiences in service. Following the original article there was quite a bit of interest from other clubs in building similar locomotives and it would be interesting to hear how they got on. I have a list of component specifications and suppliers which I will email on request - Bobbsmee@gmail.com

If anybody wants to have a look and drive Thomas Telford at the Bristol track do not hesitate to contact me and I will fix something up.

Bob
 

Vulcan

Joined: 10-01-09

Topics: 1

Replies: 8

Posted: Sun 2nd Dec 2012, 8:04pm

I own a 7.25 Vulcan loco with a single the Bosch 750 watt motor & Parkside controller. The engine is geared to 8.5 mph which in my view is quite fast enough particularly when public running. This engine will pull perfectly well with 2 very heavy passenger coaches behind plus 6 large adults plus a driving truck. Its likely that the batteries are not delivering full voltage. You don't say what type they are but its best to use AGM types suited for traction applications. If you are using an automotive type this could be the problem. If using AGMs you will also need the correct charger as AGMs require a higher charging voltage than automotive types.
 
 
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