1976 Batavus HS50 electric conversion

jose_p_adams

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Mar 20, 2021
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Hello everyone. This is my first post but I have been doing quite a bit of reading. I recently came into possession of a 1976 Batavus HS50 moped. The original 2 stroke gasoline engine was completely destroyed by previous owners and it is time to move on to an electric conversion. I have been doing some research on electric motors and batteries and the like and I have a few questions. There is a link below so you can more easily see what it looks like.

https://www.google.com/search?q=bat...AgXEAE&biw=1964&bih=1201#imgrc=lK4o5zUAxLRM_M

It was originally powered by a 50cc, 2-stroke engine which by all accounts I have read was underpowered for what it was. I am looking to keep the styling of the bike as close as possible to the original. I also want to keep the pedals. I will have to remove the existing gas tank and replace it with a battery/motor controller compartment which will be custom fabricated and will hopefully kinda look like the gas tank.

I'd like it to carry me up hill at 20-25 mph for a short distance and also be able to top 30 mph on flat ground. These numbers are pretty consistent with the performance that I believe that the bike was originally designed for. It has mechanical drum brakes and skinny tires so I don't want to get too crazy.

It seems to me that a 1500w motor will be a reasonable replacement for the original engine. I plan to mount the motor in the same configuration as the original engine. The original engine had a centrifugal clutch which drove a 60mm type A belt pulley. That belt was also connected to a larger idler pulley/13 tooth chain sprocket combination. That combination pulley/sprocket then drove the rear wheel with a 50 tooth sprocket. Overall, I think that the gearing reduction was between 13:1 and 14:1. There is obviously some flexibility with this in the final design and that will depend on the RPM range of the motor that I end up purchasing. It can also be modified in the future, if needed by purchasing a different pulley. I have been looking for a motor for some time and I think that the best option I have found is the Golden Motor 1500w

https://goldenmotor.bike/product/1500w-bldc-motor/

The dimensions seem to fit in the space I need and the output shaft is a keyed round shaft that I can fit the appropriate pulley to. I have looked at the QS motors but have found only 2000w motors which is probably reasonable but the physical size of them seems close enough to being too big that I am hesitant to try it.

Is this reasonable? Is a 1500w motor adequate to power a 120lb moped with a 200lb rider?

For a controller, I was planning to just get the 2000w controller that is rated for 48v and 50A.

https://goldenmotor.bike/product/bldc-motor-controller-48v2000w/

It is not clear based on the website what all is included but I guess once I find out, I can get the rest of the stuff I need to make it work. I do hope to re-use the brake levers currently on the moped. They have switches for the brake light which I believe can be integrated into a regen controller circuit. The golden controller also seems to have good dimensions to integrate into my battery/controller enclosure plans.

Finally, I will need a battery. I plan to construct my own battery pack. Due to the space available, the battery pack will need to be either 2 separate units which will be located on either side of the top tube. This will allow it to look more like a gas tank and will free up some space. I have never constructed a battery pack. I am not sure if I want to make this 2 separate packs, or a single pack. I am leaning toward 2 separate packs as that will allow use of 2 chargers which may be convenient. I am planning to use Samsung 30Q 18650 cells in either a 6p13s or 8p13s configuration. These cells seem to be a good option for this application and are supposedly rated at 15amp continuous discharge. I need to do the design work but I am going to go with the 8p configuration if I can fit it, and I think that I can. At max power, I would be relying on these cells for about 4A each. Am I on the right track here? Is an 8p13s battery pack constructed with Samsung 30Q cells adequate for a 1500W motor? I would like to have 20 miles of range at a minimum. My calculations suggest that the 8p battery will be adequate to do that but I have no experience.

Any input is much appreciated.

TLDR: I have a 120lb moped and I need to make it go the way it used to go. What size battery? What size motor? What controller?
 
jose_p_adams said:
I am looking to keep the styling of the bike as close as possible to the original. I also want to keep the pedals. I will have to remove the existing gas tank and replace it with a battery/motor controller compartment which will be custom fabricated and will hopefully kinda look like the gas tank.
You can clean out and then cut open the original tank, to use the space inside for your stuff, if there is sufficient volume. But I would not put the controller inside a compartment unless the heatsink of the controller sticks out of the compartment to be exposed to outside airflow (otherwise they may overheat, or at least have components that get hot (and those near them) age much faster than normal, and also heat up your battery, aging that faster, too).




I'd like it to carry me up hill at 20-25 mph for a short distance and also be able to top 30 mph on flat ground.
What slope of hill, and how short a distance? Those, along with a guesstimate of total system and rider/etc weight are necessary to determine how much power you need, minimum, and how capable your battery will have to be.

Another consideration is winds--if there are ever significant headwinds, and you wish to maintain speed against those, you need to be capable of as much power as the wind speed plus the maintained speed will take to achieve.


1500w is probably enough for the 30mph on flat ground with no winds, and possibly the hills and/or winds at the slower speeds, but you need to know the other info first.

This page is useful for determining system needs:
https://ebikes.ca/tools/simulator.html

Finally, I will need a battery. I plan to construct my own battery pack.

For 20 miles of range, at 30mph with no winds, it'll probably take around 45wh/mile or so, 45 * 20 = 900wh; we'll round up to 1000wh. 1000wh / 48v = 20.83Ah; we'll round up to 21Ah. Assuming you get at least 2.5Ah/cell out of those (depends on how high you charge them, and how far you discharge them), at 8p 8 * 2.5 = 20Ah, so that will probably just get you the range you want, assuming no winds and mostly continuous riding on the flats, not much in the way of hills or slopes, and not having to deal with stop/start traffic, and no detours, when the pack is brand new.

If you have a lot of stop/start traffic, and/or headwinds or it's not really as flat as you think it is, you might go up to 50 or 60wh/mile average, depending on conditions. More hills or more winds could raise that up even higher, cutting your range.

As the pack ages, it will lose capacity (and capability to deliver amps), so both for that and the other things, then if you have the space for it I would recommend adding 25-50% to your pack size, if you really need the full 20 miles of range.

If 20 miles is an outside estimate, and you really only need half to 3/4 of that, then you probably don't need to add more to the pack to account for the above.


At 8p, if each cell can deliver 4A, that's only 32A. If you have a 50A controller, then each cell will need to be able to handle 6.25A+ each. Theoretically they're 15A cells, but the harder you push them the more voltage sag and heating you have, and the less power you get at the wheel, and the less capacity you get out of them, and the less lifespan they have.
 
Being a beginner myself, I can't offer much input on the technical side of your plan.

But about this:

jose_p_adams said:
I also want to keep the pedals.

I think it is a good idea.
If you run out of electricity, pedaling is more comfortable than pushing the bike.
I really love this feature on my electric bike conversion.
Of course an electric bicycle offers a bit more comfort in pedaling than a moped, but still...
 
amberwolf said:
You can clean out and then cut open the original tank, to use the space inside for your stuff, if there is sufficient volume. But I would not put the controller inside a compartment unless the heatsink of the controller sticks out of the compartment to be exposed to outside airflow (otherwise they may overheat, or at least have components that get hot (and those near them) age much faster than normal, and also heat up your battery, aging that faster, too).

I had considered that but I didn't think there was sufficient volume to do it. However, if the controller can't live in the same place as the battery, it may work.




What slope of hill, and how short a distance? Those, along with a guesstimate of total system and rider/etc weight are necessary to determine how much power you need, minimum, and how capable your battery will have to be.

Another consideration is winds--if there are ever significant headwinds, and you wish to maintain speed against those, you need to be capable of as much power as the wind speed plus the maintained speed will take to achieve.


1500w is probably enough for the 30mph on flat ground with no winds, and possibly the hills and/or winds at the slower speeds, but you need to know the other info first.

This page is useful for determining system needs:
https://ebikes.ca/tools/simulator.html

I would estimate that it is less than 7% for about 1/2 mile. I am going to find an ap for my phone that can approximate elevations and drive the route to get a better handle. Thanks for the link. I had not seen that page before. It seems as though 1500w may be marginal for what I want to do. I can certainly consider a more powerful motor. The 25mph limit is a safety consideration. The highest speed limit road I will be on is 35mph but many people drive faster than that. I will need to cross a 0.75 mile long bridge 2x daily where vehicular traffic regularly hits 50mph. People are accustomed to cyclists being on it and have ridden a pedal bike across it over 1000 times without issue, but a little more speed wouldn't be a bad thing.

For 20 miles of range, at 30mph with no winds, it'll probably take around 45wh/mile or so, 45 * 20 = 900wh; we'll round up to 1000wh. 1000wh / 48v = 20.83Ah; we'll round up to 21Ah. Assuming you get at least 2.5Ah/cell out of those (depends on how high you charge them, and how far you discharge them), at 8p 8 * 2.5 = 20Ah, so that will probably just get you the range you want, assuming no winds and mostly continuous riding on the flats, not much in the way of hills or slopes, and not having to deal with stop/start traffic, and no detours, when the pack is brand new.

If you have a lot of stop/start traffic, and/or headwinds or it's not really as flat as you think it is, you might go up to 50 or 60wh/mile average, depending on conditions. More hills or more winds could raise that up even higher, cutting your range.

As the pack ages, it will lose capacity (and capability to deliver amps), so both for that and the other things, then if you have the space for it I would recommend adding 25-50% to your pack size, if you really need the full 20 miles of range.

If 20 miles is an outside estimate, and you really only need half to 3/4 of that, then you probably don't need to add more to the pack to account for the above.


At 8p, if each cell can deliver 4A, that's only 32A. If you have a 50A controller, then each cell will need to be able to handle 6.25A+ each. Theoretically they're 15A cells, but the harder you push them the more voltage sag and heating you have, and the less power you get at the wheel, and the less capacity you get out of them, and the less lifespan they have.

Thank you for the insight. When I did my initial calculations, i assumed 40Wh/mile. I will adjust that to be more conservative in the future. I would like this to be able to easily take me from my home to the gym to work and back home again on a single charge. That is about an 11 mile round trip. 20 miles would give me more confidence that I will make it even with some degradation. I have room for a much larger battery pack than 8p13s, especially if I move the controller to a different area. I believe I can accommodate about 320 18650 cells in the space that I have. That would surely meet my needs.

I am going to give some consideration to a more powerful motor and a 72v pack. If I were to go with a 16p20s pack and a 3000w motor, I think I would have more range and power than I need, which isn't a bad thing but admittedly, I'm a little shy about buying 320 high quality 18650 cells ($$)
 
jose_p_adams said:
I had considered that but I didn't think there was sufficient volume to do it. However, if the controller can't live in the same place as the battery, it may work.
It *could*...but generally isn't recommended. For a little 250w pedalec that probably doesn't even see 250w typical usage, it is fine...but for something depending entirely on a 2400w controller (48v * 50A), it's probably going to generate too much heat. Let's guesstimate the controller is 90% efficient; 10% of the power thru it will be wasted as heat. If you were running at 1500w average, that's 150w of heat. A 150w incandescent light bulb is pretty hot; it's a small surface area. THe controller has a few times that much surface area, so it doesnt' feel as hot, but enclose it and trap that heat.... Even if the controller is 95% efficient, that's still 75w of heat. Even 98%, that's still 30watts of heat...a small soldering iron is only 15w.




I would estimate that it is less than 7% for about 1/2 mile. I am going to find an ap for my phone that can approximate elevations and drive the route to get a better handle. Thanks for the link. I had not seen that page before. It seems as though 1500w may be marginal for what I want to do. I can certainly consider a more powerful motor. The 25mph limit is a safety consideration. The highest speed limit road I will be on is 35mph but many people drive faster than that. I will need to cross a 0.75 mile long bridge 2x daily where vehicular traffic regularly hits 50mph. People are accustomed to cyclists being on it and have ridden a pedal bike across it over 1000 times without issue, but a little more speed wouldn't be a bad thing.
My SB Cruiser trike is limited to 20mph...but in the event of a driver deciding they need to be where I am, I have a "GTFOOTW" mode that gives me a little more speed for those rare times that braking to get out of their way is not an option because of traffic close behind me, etc.

So...it doesn't hurt to have the ability. ;)


Thank you for the insight. When I did my initial calculations, i assumed 40Wh/mile. I will adjust that to be more conservative in the future. I would like this to be able to easily take me from my home to the gym to work and back home again on a single charge. That is about an 11 mile round trip. 20 miles would give me more confidence that I will make it even with some degradation. I have room for a much larger battery pack than 8p13s, especially if I move the controller to a different area. I believe I can accommodate about 320 18650 cells in the space that I have. That would surely meet my needs.
Probably. :) Just make sure you get *good* cells from a known-good seller, because there's plenty of places that will sell you whatever you ask for...just wait a minute while we get the shrinkwrap machine and printer fired up. ;)



I am going to give some consideration to a more powerful motor and a 72v pack. If I were to go with a 16p20s pack and a 3000w motor, I think I would have more range and power than I need, which isn't a bad thing but admittedly, I'm a little shy about buying 320 high quality 18650 cells ($$)
Another option if there is space for them is using used automotive EV-grade large-format cells, like the Nissan Leaf, etc. There are also many lithium starter batteries out there also made from large-format cells. Most of them are rectangular and flat, and make book-like stacks, but are typically pretty easy to interconnect (much easier to build with than 18650s). I don't know what cost per wh is these days, but there are places like Jag35 and Batteryhookup that salvage some of these kinds of things, and they can be worth it when they've got them. Cant' remember names of other places that carry tehm, but you may find someone tearing down a scrapped EV and might be able to buy some of the pack.


For the motor, as long as what you get is really rated to run at the 1500w "all day long", and all you really need most of the time is that 1500w, and you can add some active cooling (fan, etc, that only needs to run when it's hot), you can get away with using that at a higher power level for some amount of time. How much time depends on the specific load it's under, and environmental conditions, etc. If you can keep the magnets and windings cool, you can run it higher than intended until they aren't cool anymore. A motor *is* designed around a certain amount of current in the windings to make a certain amount of magnetic field, and above some point (saturation) more current goes into heating the motor than making spinny power ;) but as long as you're below that point, good motors generally tolerate a fair bit of abuse.

So your real limitations are your battery pack (has to provide all the power the system uses), and the controller (has to feed the motor the power from the battery as demanded by the load on the motor).
 
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