1974 Yamaha tx500 conversion
I have started to convert a 1974 tx500, and started a wordpress blog to share updates with friends who are curious about the project.
I've been researching for weeks, and have piles of components on their way. It's a relatively common selection of parts - 72v me1003 kit bought from evdrives, and a bunch of cosmetic changes to the bike that will also lighten it up.
The one thing that is not conventional (as far as I know) are the batteries. I will be going the jehugarcia way and making packs of 18650 cells. And in this regard, I have some questions if anyone is interested in walking through my attempted calculations.
Much of what I have done is try to poll the builds on evalbum that use the same motor, and then try to estimate the number of 18650 cells I would need to replicate their approximate stated ranges.
Here's an example:
guy has the same motor as me @72v pushing an '88 fz600 http://www.evalbum.com/5229
he's using 24 60Ah 3.20 Volt, Lithium Iron Phosphate packs and has about a 50 mile range
24 in series gives him 60ah @ 76.8v
if each one of my 18650s is about 2ah, and I theoretically have strings of 20 to give me 74v, each string of 20s will give me 2ah @ 72v
I then need 30 strings of 20 to equal 60ah (20s30p) 30 x 20 = 600 individual batteries
So question #1 is does this math look right?
Question cluster #2 involves a comment jehugarcia made that said that if you need a 10kw battery, then making a 20kw battery will reduce the draw in each cell by about 50%, and greatly extend the life of the battery. So my question then is how is the needed battery size calculated? measured load after I build it? Is there any way to approximate average continuous load given the motor stats which are measured without any load?
Question #3 is related to charging configurations. I saw one guy who scrapped one big charger that burned out for 6 smaller ones, but I'm not sure why. Maybe cost? If I construct my battery packs into bundles of 12v 24v 36v or 48v then string them together in series to give me 72v total does that make the charging simpler or cheaper? Would I have to install a disconnect switch to break the series connections, thus lowering the voltage requirements. I believe a simple 24v 2amp charger costs a mere $16 or could I get away with those cheap chargers on bmsbattery.com? If so which one? I don't understand the feature differences.
Sorry...I was doing a lot of thinking out loud there.
Any advice you can provide me will be greatly appreciated.
Last edited by electrictx500; 21 November 2016 at 1202.
This looks like it will be a great build.
Regarding question #1, I think your math is correct. But what about making the system voltage higher? I think your components are all good up to 90V and I think you will want the extra speed. I haven't seen the Alltrax SR series before and I'm eager to hear if it works well.
On question #2, if you are making this large pack (60Ah at 72+V) with a battery type capable of high discharge rates, I wouldn't worry any more about it. I'll skip on question #3, someone else who has tried it can answer.
One last thing: would a bigger rear sprocket (more than 50 teeth) fit on the bike? I think more teeth on the back would give you more options on the front. I really would like a bigger back sprocket so I could use a bigger front, as it seems to me the larger front sprockets make the ride experience quieter and smoother. I happen to have 50T on the back also, only because it was the biggest one available and custom might have been problematic for me.
Keep us posted!
Thanks a lot for your reply!
Your bike was actually one that I came across as I was looking for example conversions to poll. I see on your blog that you're running a 13 front sprocket. I have a 14, and a 15 sitting here. Have you tried larger ones? Was your acceleration unacceptable? I have not started building the batteries yet as it takes for___ingever to sort and measure the capacity of all these batteries so I might consider bumping the voltage up. I also haven't bought any bms's yet so I'm not locked in to a voltage yet.
I started with 13T front sprocket. Then I went to 14, then 15, then back to 14. Comments are in post #35 here. I would prefer to have ~60-70 teeth on the rear which would give me more options for larger front sprockets. I felt it got noticeably quieter/smoother with each bigger front sprocket, but I had to back down to the 14T for performance. Having said that, many people on this site are using front sprockets of 12 or 11 teeth and generally they're not complaining.
Well since you are running a more volts than me, it sounds like 14 will be the biggest I will put up with. You should get a custom sprocket made. Your's might be cheaper since it's just a giant ring. I got mine from sprocket specialists (well I ordered it...haven't heard a peep from them, and it's been at about a week and a half), and it cost $130.
Originally Posted by Lunchbag
I've been working on the conversion as parts trickle in. Still waiting on my rear sprocket from sprocket specialists...ordered 2 whole weeks ago, and not so much as a peep. Cannot ever get through on the phone...it's a busy signal all day every day.
But I have the motor mounted, and the front end almost back together:
It would be fun to try, however it would require some precise milling. It's not just a 2-dimensional ring but has a recessed area which would have to fit precisely against the rear drum which it bolts to. Could be done, I'm sure, but I just went with the biggest sprocket available in aftermarket parts.
Originally Posted by electrictx500
Depending on the depth of the recess, and your frame clearance you might be able to just mount a flat ring, and nudge your front sprocket over a bit. I just checked the sprocket specialist site, and they have no listings for anything Royal Enfield, but they do claim to be able to make anything you want from your measurements, although at this point, I cannot recommend them since it's been 17 days since I placed my order and still not a peep. Their phone line is a busy signal all day, every day, and I've yet to receive a reply to email or facebook messages. I can't imagine trying to place a totally custom order with a company that is so difficult to communicate with.
Originally Posted by Lunchbag
I am copying your electrical schematics, and would appreciate any tips or extra components, fuses, diodes, etc you might recommend. I'm hoping to hunt down a cheaper and smaller charger though.
Edit: Just received a facebook reply from sprocket specialists - sprocket should be in the mail within two days. woot!
Last edited by electrictx500; 06 December 2016 at 0806.
Why are they recommending a "series" motor controller for a Permanent Magnet motor? Series have 4 connections (S1, S2, A1, A2). The ME1003 only has 2. It seems like you're going to have to unnecessarily bridge two of the terminals on the controller. The SPM72400 is more appropriate for the ME1003.
I'm going to be doing a SPM 72650 on mine with the ME1003 for stupid torque.
When you look at the alltrax controller page http://www.alltraxinc.com/Products_SR.html on the right side they list all their controllers under "old part" "new part" and all the spm controllers have been replaced with the sr controllers, except for the one you are using, for which they have no new part listed.
But your question is over my head as I don't understand the difference between a series motor, and a perm. magnet motor. The wiring diagram for "generic no reverse" (also on the lower part of that page) does show a series motor connected to the controller, but only by two connections + and -. http://www.alltraxinc.com/files/DOC1...V-WIRE-DIA.pdf
EDIT: I just noticed the "permanent magnet, no reverse" diagram: http://www.alltraxinc.com/files/DOC1...V-WIRE-DIA.pdf
Last edited by electrictx500; 19 December 2016 at 0703.