PINNED - Lithium battery conversion/info

[LROBBINS]

Having access once again to the Roboteq site, I've done a little checking on those controllers.

(1) Difference between XDC and HDC controllers. The only difference I can see is the number of input and output pins - the XDC has many fewer. Of most importance, there are only two digital outputs. If that's enough, no problem. BUT, the the U.S. price for the HDC is all of $20 more than for the XDC, and the EU price is E25 more (but includes VAT and import fees). They must have a backlog of HDC orders at the moment, as there's an 8-week lead time for these.

(2) The MDC1460 is a lower-powered single-channel controller that may be well matched to your scooter (> twice the power of your current controller may well be enough - John can you chime in on this?) and is a lot cheaper. It also has only 2 digital outputs, so you will have to think hard about whether you can get by with just 2. What do you need to control other than the motors? High-current contactor, brakes, backup beeper, horn, lights? Are you prepared to design separate controls for these if you can't do it all from the motor controller?

(3) I did not see any minimum order amount for on-line orders, nor did I see any pricing in GBP. I would still order from the U.S. - at least there's then a chance of getting the reduced VAT rate for disability products (0% in the U.K.), whereas the Euro prices automatically include VAT (and I think they Fedex ship from the U.S. anyway). Dealers/distributors have a BIG markup as well as probably not having the skills/equipment to diagnose any failures. If you do have a controller failure, even having bought in the U.S. you will probably be referred to the Swiss service center or Paris development center (their chief programmer lives in Paris) rather than being asked to return the unit to the U.S.

(4) Accessories. None of these are really proprietary items, except the license for Roborun+ v1.8, and they would be either cheaper elsewhere or fairly simple DIY.

Roborun+ v1.8 has some bells and whistles not in 1.7, supports some newer controllers not supported by v1.7 (but none that you are looking at), the license is very expensive, and v1.8 is unusable on computers with a 19:7 wide screen. Version 1.7 is no longer on the Roboteq download page, but I have written permission from them to give a copy to anyone who needs it. They have also said they would be willing to help people with disability projects, and I have a contact for that if you decide you do want 1.8 - they would probably give you a free copy.

I do recommend buying a USB isolator (or USB to RS232 adapter + USB isolator) to protect your PC if something goes badly wrong in the Roboteq - but don't buy it from them.

[Burgerman]

(2) The MDC1460 is a lower-powered single-channel controller that may be well matched to your scooter (> twice the power of your current controller may well be enough - John can you chime in on this?) and is a lot cheaper.

Well, not sure! Depends on what he wants as an end result and the motor spec!

[Scooterman]

What do you need to control other than the motors? High-current contactor, brakes, backup beeper, horn, lights? Are you prepared to design separate controls for these if you can't do it all from the motor controller?

(2) The MDC1460 is a lower-powered single-channel controller that may be well matched to your scooter (> twice the power of your current controller may well be enough - John can you chime in on this?) and is a lot cheaper.

Well, not sure! Depends on what he wants as an end result and the motor spec!

Hi, thank you Lenny & BM.

Regarding my scooter I believe the lights and indicators are on a separate circuit. I've not got the wiring diagram for my scooter but believe the s-drive is wired up similar to this

I will ask someone to give me a hand lifting the seat off and then I will disconnect the s-drive and see if the lights and indicators still work?

Re: the Roboteq inputs/outputs.

Inputs: Wig-Wag throttle input (accelerate/fwd/rev) which is a potentiometer.
Tortoise & Hair (a simple push button)
Speed dial (min/max) another potentiometer. Which limits throttle input.

Outputs: One Motor
Electric Brake

My scooter motor is rated at 800 watts continuous. But I've read it can cope with 2600 watts peak?

Screenshot 2018-12-11 at 14.07.01.png (316.47 KiB) Viewed 4544 times

The scooter works well as it is, but as I'm planning to convert it to lithium (for more range), I thought that it doesn't add too much more expense to double it's speed on the flat. It's a big scooter and the chassis could easily cope with 20mph on smooth roads. But it doesn't mean I would be travelling at that speed everywhere. It would just nice to have it for long straight smooth tarmac roads.

But I haven't the technical or computer knowledge to be confident to do it myself. I can do all the physical stuff rewiring etc. But I wouldn't be confident about being able to set up the Roboteq by myself. But as long as yourself and BM are around via this forum then that would give me enough confidence to have a go. But it won't be until after xmas now. I will do the lithium conversion first, get the 16 cells running in 2P8S arrangement, then buy the roboteq and reconnect them 16S.

[Burgerman]

Amps on the controller you have now?

[Scooterman]

Amps on the controller you have now?

120

[Burgerman]

Any controller with 120 or more Amps will give a torque or heat increase if you *use* that increase. As in at a low 24V at slow speeds as you climb a ramp or a curb. And at 48V everytime you accelerate hard to well beyond half speed.

At 120A when stalled against a curb, or at max acceleration from 0mph your motor draws 120A limited by the controller, x 24V = 2880 WATTS. But only until the wheels begin to turn, then the current naturally falls away as you begin to speed up.

On 24V that 2880 watts can be maintained until around 2/3rds speed if you let it. Will that hurt it? Thats up to you, the rate of acceleration, any hills, weight of you/scooter, and the motor construction.

[Scooterman]

Thank you BM.

I suppose what I could do is use the tortoise/hare button as a 24/48v boost switch via one of the Roboteq's digital inputs? That way in "tortoise" mode the roboteq would limit the motor volts to 24v. But when on a level or downhill section I could select "hare" mode and the controller would deliver up to 50v to the motor?

I've got an old Robin amp clamp that I kept from work. I'm not sure if it does dc though, but I know it's rated to 2000 amps ac. Could I clamp it round one of the battery cables and measure the amps going to the motor? It would be difficult to clamp it around one of the motor tails and still be able to see the amp clamp while riding along. It would still be difficult seeing it when clamped around one of the battery leads, but with the scooter's body work off I might be able to hang over the side of the scooter and see the amps when riding along flat out at 9.5mph in it's standard 24v form.

It might give me a rough idea of what the motor will draw at 50v 20mph. Because didn't you say double the voltage, it doubles the amps + a certain percentage to allow for the additional wind resistance at 20mph?

If the calculated figure is above the 42A motor rating then I know I won't be able to convert it to 50v. But I would still do 24v lithium as imo 3x range is the greatest benefit of lithium. As well as flat discharge curve, deep DoD, and lots of cycles.

[Burgerman]

Thank you BM.

I suppose what I could do is use the tortoise/hare button as a 24/48v boost switch via one of the Roboteq's digital inputs? That way in "tortoise" mode the roboteq would limit the motor volts to 24v.

You could.

But when on a level or downhill section I could select "hare" mode and the controller would deliver up to 50v to the motor?

Yes. But even at half speed, max acceleration would still allow you to give the motor full controller Amps since its impedance is the same and now you have 2x the volts! So you COULD still accelerate hard enough to heat it up. Depends on variables like weight, impedance, and acceleration rates set.

I've got an old Robin amp clamp that I kept from work. I'm not sure if it does dc though, but I know it's rated to 2000 amps ac. Could I clamp it round one of the battery cables and measure the amps going to the motor?

No you can measure MOTOR amps, and battery amps are entirely different thing!
I will have another quick go at explaining.
At 6V at the motor approx - it will be a 25% pulsewidth to linit it to the 120A. So thats 120A at the motor, and 30A at the 24V battery...
At the SAME 6V at the motor, it will pull the same 120A limit, which is now only 12.5% pulsewidth on a 48V battery...

READ THE ABOVE TWICE!

As you speed up and accelerate away at max power, the Amps that the motor pulls falls away naturally, and the controller can use a wider pulsewidth as you gain speed. At some point the FULL pulsewidth = 120A at the motor. Now battery Amps and motor Amps are the SAME. This happens at DOUBLE the speed on the 48V chair. From the point where the 120A limit is no longer needed, the motor amps, and the battery amps are the same, and fall away to a low figure once you are flat out. And the motor unloaded and no longer accelerating..

It would be difficult to clamp it around one of the motor tails and still be able to see the amp clamp while riding along. It would still be difficult seeing it when clamped around one of the battery leads, but with the scooter's body work off I might be able to hang over the side of the scooter and see the amps when riding along flat out at 9.5mph in it's standard 24v form.

Which wont tell you the motor amps.

It might give me a rough idea of what the motor will draw at 50v 20mph. Because didn't you say double the voltage, it doubles the amps + a certain percentage to allow for the additional wind resistance at 20mph?

I didnt say that, no! Although when you are at full speed, the motor amps and battery amps will be very similar. And basically if you lift the wheels off the deck will be around 5 to 8A. If driving you along, depends on friction, air, tyres, hills or how level etc will be more... And vary. At this point it will be below your motors rated average watts.

[Scooterman]

Thank you BM I read it twice and totally get it now, I didn't think of it that way.

(6V x 120A) at motor = 720 watts
(24v x 30A) at battery = 720 watts

But as you say under no load the motor is getting the same volts as the battery voltage, so motor amps and battery amps will be roughly the same.

But at full throttle (for a prolonged time) providing the amps stay below 110A (see attached 120A s-drive settings)

the motor will being receiving 24v.

So does that mean with 50V and a roboteq set up to the same motor specs as the s-drive, i.e 110A continuous and 120A boost then I can't cook the motor as the amps will be limited to 110A. So the scooter might or might not be able to manage 20mph on the flat depending on whether the amps stay below 110 amps?

But that doesn't sound right because the the motor is rated at 42A continuous but the s-drive can deliver 110A continuous.

Does that mean that in it's current 24V form the motor could receive more than it's rated 42A for a continuous period of time when going up a very long steep hill. Why isn't the s-drive programmed to limit the continuous amps to 42 amps?

I must be missing something?

[Burgerman]

Heres what you are missing. A motor is also a generator. Forget that 80A on the motor its meaningless. Its also wrong! Since 24V x 80A is over 1000 watts.

Apply 24V to your stalled motor, and depending on its impedance it will draw 200A? Maybe more as impedance shows as 25mOhm, maybe less. But the controller limits it to 110A. Or whatever is set.

Now... if you are traveling at max speed, on a 24V scooter, the motor is generating almost 24V. So almost zero current flows if you add 24V. As you speed up, Amps fall because the motors voltage and the battery voltage get closer. So the controller adjusts the pulsewidth as you get faster to maintain a max 110A until it no longer needs to do that. About 1/2 speed on a 24V scooter.

Volts = RPM.
Amps = Torque.

But if your scooter and its motor is traveling DOWNHILL at a little faster than your normal top speed, the motor may be at a higher Volt level than the battery. And this motor cannot draw ANY current. Quite the opposite, it charges the battery.

So if you travel at full speed (or constant speed) on your scooter that is the LEAST current that will flow. But if you accelerate, with 48V you can do so at MAX limit amps, right up to around 2/3rds your new top speed.

[Scooterman]

Ah thank you BM, I remember now it's the back emf. I'd forgotten about that, we learnt about that in college.

"A motor has coils turning inside magnetic fields, and a coil turning inside a magnetic field induces an emf. This emf, known as the back emf, acts against the applied voltage that's causing the motor to spin in the first place, and reduces the current flowing through the coils of the motor"

Thank you reminding taking time to explain BM. I'm pleased I understand now.

[foghornleghorn]

Whenever I'm going downhill you can feel the wheelchair leaning on the motors to stop it rolling away to a spectacular crash at the bottom - is it charging itself every time?

[Scooterman]

Whenever I'm going downhill you can feel the wheelchair leaning on the motors to stop it rolling away to a spectacular crash at the bottom - is it charging itself every time?

Yes I think that's called regenerative braking. I had it on a vw golf I once had.

[foghornleghorn]

Now I want to find somewhere with a 30 mile downhill run and see if I get to the bottom still fully charged

[Scooterman]

Now I want to find somewhere with a 30 mile downhill run and see if I get to the bottom still fully charged

BM has a good video which demonstrates it. If he see this he might attach upload it.

[Burgerman]

In my local shopping centre I spent hours once going up in the lift, and going down the big spiral road in the multi story car park to charge my batteries a bit...

Whenever I'm going downhill you can feel the wheelchair leaning on the motors to stop it rolling away to a spectacular crash at the bottom - is it charging itself every time?

Yes and every time you decelerate.

[Scooterman]

I bet you got a few queer looks from fellow shoppers.

[Scooterman]

(3) I did not see any minimum order amount for on-line orders, nor did I see any pricing in GBP.

Hi Lenny, I just registered on the Roboteq website and my account shows MIN PURCHASE 800. I assume that means $800 dollars but maybe it means 800 controllers! Lol (just joking the last bit)

[LROBBINS]

Strange, I never registered on the Roboteq site yet have had no problem ordering. When you're ready, try to order a single controller and if there are problems we'll "talk" to someone there. I suspect that there won't be problems, however. That $800 may just refer to purchases "on account" and I'll bet they have no problem accepting a credit-card web order for a lot less.

[Scooterman]

Thank you Lenny.

I emailed Roboteq support this morning. I attached my motor's specs and s-drive settings and ask them if they can recommend the most suitable model controller for my application.

I'm hoping I'll receive a positive reply.

[Burgerman]

You dont know your motor specs.

[Scooterman]

You dont know your motor specs.

No I suppose I don’t. On hindsight the nameplate isn’t the ‘specs’.

BUT! Maybe the ‘Motor’ parameters in the s-drive settings will give them enough? Afterall, they don’t have idiots like me working for them

[Scooterman]

I found this. http://www.linix.com.cn/detail.aspx?cid=1120

it's a shame it's in Chinese. I guess Linix is a Chinese company.

[expresso]

http://translate.google.com/translate?h ... cid%3D1120

[Scooterman]

Wow that's a good translation Expresso!

Thanks

[Scooterman]

https://rover.ebay.com/rover/0/0/0?mpre ... 1593337188

Hmmmm

[Burgerman]

What roboteq need.

What is the average load?
Max load?
What is max motor efficiency and at what RPM/LOAD?
What is motor impedance?
What is max allowable current before magnet deterioration or saturation?
What is the free running current at say 12, 24, 48V
What is stall current at 12V

[Scooterman]

I don't know any of them figures.

I think I will knock the idea of 50v lithium on the head. If the motor burnt out it's easy enough to buy and fit a replacement, although I'd rather not go to that expense.

It's all the re-wiring work that I wouldn't want to do if it didn't work or the motor failed after a few days. And then what would I do? Replace the motor and run the 60v roboteq at only 24v? What's the point of that? Or re-wire back AGAIN and refit the 24v s-drive!

All that work, expense, and head scratching for nothing.

No I'll leave it as it is and just fit lithium cells and be satisfied with loads more range.

But it was worth exploring the idea, and I learnt something.

[Scooterman]

BM - on the main site when describing your first lithium conversion you said than some controllers might trip on over voltage as 8 x series lifepo4 cells give slightly voltage than say 2 x MK gel batteries.

If I fitted 8S lifepo4 to the scooter and the s-drive kept on tripping. Is there a work around to prevent it happening?

[Burgerman]

When fully charged the voltage is high immediately after charge. If it gives an error, then wait 15 mins... It will drop to a sensible level.
Or charge to 3.550V per cell instead of the manufacturers 3.650V. Or the 3.600 we tend to use.

It drops to 3.45v naturally if you wait a bit regardless. So dont worry.