# Is this design ok? 48v , 120ah



## mattW (Sep 14, 2007)

Well if you have already bought the motor then your top speed is limited by its existing power rating, putting more amps through the motor will cause it to burn out. If your motor can only handle 48V @ 125A then your power will be 6kW continuous from the controller and at 85% efficiency you will get 5.1kW output from the motor... I'm not sure if you will be able to travel at 60mph at that speed especially considering the poor aerodynamics of motorbikes, but you will have to work that out...

What I can tell you is that at your top speed (whatever that is at 125A) you will be able to travel at that speed for an hour for every 6kWh of energy (a lot on a motorbike) in your battery pack. Lower speeds will mean a longer range.

72V means you can have more smaller batteries, less transmission losses in the cables due to heat and more peak power. I'm going with 72V 60Ah lithium for a top speed of 60mph and a range of 50 at 40mph cruise... I don't think you'll get what you want with lead acid though.


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## flashedarling (Jun 30, 2008)

I haven't bought the motor yet, I'm trying to confirm what would constitute a good design before I go for it. So you are saying that peak power is what determines top speed, which is good to know and part of my question.

What kind of batteries are you using then? I haven't seen many 60AH Lithium batteries.

Is it always the case then that you'll want a higher voltage to reduce the Amps and therefore the AH you'll need?


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## Qer (May 7, 2008)

flashedarling said:


> Is it always the case then that you'll want a higher voltage to reduce the Amps and therefore the AH you'll need?


Yes. In the end the power you get out of a motor is the amount of Watts you take out of it. The power (Watt) is Amps multiplied with Volts so if you increase the Voltage the Amps go down.

Of course, if you increase the voltage of the battery pack the controller and motor must be chosen accordingly. As you can't run a 12 Volt bulb on 24 Volts you can't run a 48 Volt motor on 72 Volt (at least not for long).

And of course this is a simplified explanation and there's lots of other variables and things to consider. Of course.


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## frodus (Apr 12, 2008)

many motors can handle twice the rated voltage with no issues. Timing may be needed beyond that. Below 100V you should be fine, Just search for threads related to Jim Husted on this site.

Your top speed is limited by volts. Motors have a volts/rpm rating, or a curve that shows the increase in RPM per given voltage.

Plenty of people have used the etek at 60 and 72V. Search EVALBUM.

I'd find it much easier to fit in smaller batteries, lower Ah, than 4 really huge batteries.


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## major (Apr 4, 2008)

flashedarling said:


> I haven't bought the motor yet, I'm trying to confirm what would constitute a good design before I go for it. So you are saying that peak power is what determines top speed, which is good to know and part of my question.
> ?


Hey flash,

I don't want to put words in mattW's mouth, but.....Peak power for top speed? Maybe, if you want top speed for a couple of seconds. Otherwise, you should consider rated power for top speed. Or hill climbing, which ever is more.

I see guys using these PM motors for cycles. No hands on experience with the Etek, but I recommend you look at a nice wound field motor. They are superior in durability.

Regards,

major


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## frodus (Apr 12, 2008)

Qer said:


> you can't run a 48 Volt motor on 72 Volt (at least not for long).


Where did you get that information? Experience? Manufacturer data? Physics calculations?

So all those people on EVALBUM running with Etek motors at 72V are wrong? All those people running the K99-4003 and the A00 and A89's are wrong too?

Do you have factual data showing that the 48V motors can't be run at higher voltage? I seem to remember lots of those motors (including the one in my motorcycle), being able to go much higher. In fact, the manufacturer of my motor ADC, has curves on my 48V motor going to 96V. The issue is not voltage, as much as it is the timing of the brushes. Timing advancement and structural reinforcement of the armature may be needed depending on how much the motor is being overvolted.


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## frodus (Apr 12, 2008)

major said:


> Hey flash,
> 
> but I recommend you look at a nice wound field motor. They are superior in durability.
> 
> ...


I second that! At higher RPM's and higher load (highway speed) you will have cooling issues with the Etek. A motor with a larger thermal mass and a built in fan might be a better choice. look at the A00 and K99 from Advanced DC and the ES-31 from D&D.


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## Qer (May 7, 2008)

frodus said:


> Where did you get that information? Experience?


Experience, but not from EV's. Yes, you can apparently run an EV-motor out of specs, but not continuously. You can increase the time or level you can overload it by adding cooling (the movement of the vehicle provides some extra cooling in itself) but if you overload it too much or too long it's eventually going to break.

If you have an EV where an ADC or Warp 9 runs at 144 Volts (which seems to be pretty popular) it means that it will peak at 144 Volts (or rather it'll probably peak even lower since the battery pack voltage will drop at heavy load, like when accelerating). Cruising will be performed at lower voltage (due to PWM) which will mean much less power out and thus give the motor time to cool down again. As long as the motor doesn't spark and it doesn't runs too hot it's reasonably safe to run it at over voltage.

Why I want to add a word of caution when it comes to running a 48 Volt motor at 72 Volt is that 72 Volt means that the motor will generate more than twice the power it's specified for and since a small motor might be a bit on the weak side to begin with (I mean, there must be a reason why many EV-MC's run at more than 48 Volts), it might mean it won't get the necessary time to cool down while cruising. Also, a small motor overheats faster too (less mass).

I believe an ADC 4001 and WarP 9 are both specified to run at 120 Volt. To peak them at 144 Volt is like running a 48 Volt motor at 58 Volt. Running a 48 Volt motor at 72 Volt is like running an ADC 4001 or WarP 9 at 180 Volt. It's possible (at least some people has claimed to do it successfully), but it's also quite possible that your nice WarP 9 turns into a very expensive (and heavy) paper weight when you try.

Personally I've burned motors quite definitely at much less than 50% over voltage. I wouldn't dare unless the motor was free or at least very cheap. But hey, as long as you're prepared to take the risk, go ahead! As I said, the risk you're facing is that you get yourself the mother of all paper weights.


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## Little Rhody (Jun 17, 2008)

Qer said:


> As I said, the risk you're facing is that you get yourself the mother of all paper weights.


I have some of those around the shop. (not all motors) 

Lr


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## flashedarling (Jun 30, 2008)

I read that the Etek motors are sometimes more fragile but I was under the impression that the Brushless Etek Permanent Magnet motors were more reliable than their brushed cousins. 

I'm still not certain if I want to change to a 72volt design. The order of my priorities are :

Range
Cost
Top Speed
Noise

I'd be fine with a 50-something top MPH which seems typical of the 42v Etek. Since I'm planning my commute on avoiding highways I my avg speed should be around 40mph. I also assume that a 42v brushless motor would be quieter than a 72v wound motor. However I have no basis for this. If you know what the quietest option would be that would help factor into my decision.

I'm looking at a Yamaha FJ1100 or FJ1200 right now. So having a tighter fit of batteries would be nice, I'm not sure that I save room though, since even though I would need less AH I'd need 2 more packs.

I could really go either way, I just need some convincing on what is best for me. I'm getting the impression that more people here go with the >72v option though while there are quite a few people on EVALBUM who go with the 48V option.


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## frodus (Apr 12, 2008)

48V and that large bike is a pretty heavy load for the etek... its going to heat up.

Find the bike weight, and rider weight, calculate what HP would be required to stay at 50mph, or calculate the acceleration desired and see what torque is needed.

I still think the Etek is a bit on the light side, especially for an 1100 or 1200 with a stock weight of 600+lbs.

Todd Stiers on Evalbum has a Kawasaki ZX-11, 60V and an etek, and its not bad, but tops out around 45 or so. You may get that top speed if you gear it right, but its going to suck amps, heat up at lower RPM's and take forever to accelerate to speed. They're good little motors, but size the motor according to the bike... you can't just throw it in anything and get what your requiring.


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## flashedarling (Jun 30, 2008)

Alright I think I'll go with a 72V motor. My only worry is how this increases costs. What would be a good 72V motor? I've currently selected a PMG-132 which seems to fit my need save it is a little pricey. I've also had to factor in unexpected mechanical and electrical costs.

Here is what I have so far, I found a handy spreadsheet from a guy on EVALBUM:
http://spreadsheets.google.com/pub?key=phfWrPZIh7BNZXlJ_KbdAOw

With these calculations I should have more than enough range and could probably get less AH batteries, but I'm going with basically Generic AGM batteries and I don't know if I could find a better price.

Is there something terribly wrong with my estimates? Am I picking out more expensive components than I need?


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## frodus (Apr 12, 2008)

the k91 is a good motor, for about 750, and the a00 is around 550-600.

http://www.electricvehiclesusa.com/product_p/mo-k91-4003.htm
http://www.electricvehiclesusa.com/product_p/mo-a00-4009.htm

kta has good prices
http://www.kta-ev.com/catalog.html 600 for the A00 and 700 for the K91

ADC has good service, lots of replacement parts, and easy to rebuild. Don't know about D&D, but they look good too. I'd say the A00 would be good for you.

there's PDF cutsheets on them if you search google.
http://www.evmotors.com.au/products/download/K91-4003.pdf
http://www.evmotors.com.au/products/download/AOO-4009.pdf

I'd chose the K91 (Because I have good experience with it, and so do others with a motorcycle. Allows for a little flexibility. Its 56lbs.


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## frodus (Apr 12, 2008)

flashedarling said:


> Alright I think I'll go with a 72V motor. My only worry is how this increases costs. What would be a good 72V motor? I've currently selected a PMG-132 which seems to fit my need save it is a little pricey. I've also had to factor in unexpected mechanical and electrical costs.
> 
> Here is what I have so far, I found a handy spreadsheet from a guy on EVALBUM:
> http://spreadsheets.google.com/pub?key=phfWrPZIh7BNZXlJ_KbdAOw
> ...


432 lbs in bats is way high, you would be fine with HALF that. maybe some 55 or 60Ah SLA's. estimate about 125watt hours/mile cruising and if you have a 5000wh pack, it'l get you 40 miles.


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## flashedarling (Jun 30, 2008)

frodus said:


> 432 lbs in bats is way high, you would be fine with HALF that. maybe some 55 or 60Ah SLA's. estimate about 125watt hours/mile cruising and if you have a 5000wh pack, it'l get you 40 miles.


I guess you are right about the weight but still it is hard to say no to the heavier batteries. It seems like the more AH the better the AH/$ and AH/lb ratios. More bang for your buck so to speak. Also I'm cautious, since don't want to estimate too close and have my commute take too much battery draw. I'd like something around 60-65Ah to be safe but that doesn't seem to be a denomination they make. When you go up to 75Ah most AGM batteries are only 10 pounds lighter (70 lb) than going all the way to 100Ah. 

So right now I'm just trying to figure out how to balance the Weight-Ah-Cost equation. Honestly I'd go Lithium but my limits on cost keep me from paying more than $0.5/watt-hour.


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## flashedarling (Jun 30, 2008)

Alright here is what I'm thinking. 

*Mars ME0709 72V motor

6x Generic 12v 65Ah AGM - 50 lb each

*Is this Mars motor pretty good? The specs I saw said around 3200 rpm and 8hp (180 lb-in) continuous. This seems to be about up my alley. Then I'll go with some cheap AGM batteries. Since my commute is around 30 mi round trip and I don't want to go below 80% DOD my calculations show me getting around 48 mi total range, so as long as I get close to that I'll be ok I think.

Updated Sheet
http://spreadsheets.google.com/pub?key=phfWrPZIh7BNZXlJ_KbdAOw
* 
*This looks ok to me, I'm just afraid of once bought and put all together it won't have the necessary range.


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## frodus (Apr 12, 2008)

flashedarling said:


> Alright here is what I'm thinking.
> 
> *Mars ME0709 72V motor*
> 
> ...


that motor is basically a mars motor, not sure how they work highway speed.

Also, that calc sheet is wishful, you may not get that far depending on the rolling resistance of your motorcycle.


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## flashedarling (Jun 30, 2008)

frodus said:


> Also, that calc sheet is wishful, you may not get that far depending on the rolling resistance of your motorcycle.


Yes I understand that the calculations will always be more optimistic than the actual vehicle. What I'm asking is if they are TOO wishful. As long as in practice I can extract a 39mi range I can make it to work and back with 80% DOD which seems to be the max you can go without damaging the batteries. Right now I calculate 47mi range so what I want to know is if am I being too optimistic and if I won't even make even 39mi range or if this enough room that I should be able to make at least 40mi fine.

In other words, do I need to upgrade to a higher Ah battery to be certain I will have adequate range. Also after looking at the A00 and the K91 it seems the Mars is the best choice for me and I was wondering if I'm mistaken on that count as well.


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## frodus (Apr 12, 2008)

I'd honestly stop designing the electrical system until you've got a donor.

I just think you'll be disapointed if you put a mars in a 600cc+ size bike, and you won't fit the bats in a 250cc. Look at the HP rating. Why do you think mars is the best for you? you don't even know what bike you're getting.

I think 40 is doable, but you'll need large batteries and 5kWh them, to get that far... estimating that you're Wh/mile is less than 125Wh/mile.


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## Qer (May 7, 2008)

flashedarling said:


> As long as in practice I can extract a 39mi range I can make it to work and back with 80% DOD which seems to be the max you can go without damaging the batteries.


80% DOD won't literally damage the batteries, but it will decrease the amount of cycles you'll get from them before they need replacement. If you're going to run them down to 80% DOD on a daily basis your batteries might not even survive a year of commuting. On the other hand, by that time perhaps LiFePO4-batteries are more available and if you put those in your bike range won't be a problem anymore. 

And of course, just a few less percent DOD will increase the amount of cycles a lot so the only way of finding out how bad/good it's gonna get is to actually try! Don't let my word of caution stop you!


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## flashedarling (Jun 30, 2008)

Since I won't use this every day, such as when the weather doesn't permit, even 500 cycles would be enough for 2 years. I'm going to leave off finalizing parts until I've got a bike but I believe I'll need almost 5kW-h like frodus suggests. Now that either means 6-12V,88Ah SLA batteries which would be around 360lb or more, or switching to lithium, now I'm just starting to research lithium batteries and I can't seem to find an option with a cost less than $0.90 which means I'd have to spend almost 5 grand on a battery pack! Which may be beyond my price range. 

Also I don't know enough yet about lithium batteries and managing them to make an educated decision. So I'm torn, I need a ton of power but either I have to take on alot of weight or spend a ridiculous amount of money. I'm tempted to see if I can get away with that much weight but I don't know enough to estimate that. So I'm just trying to learn as much as possible while I get my license, then when I buy a bike I may start a new thread.


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## Qer (May 7, 2008)

flashedarling said:


> Also I don't know enough yet about lithium batteries and managing them to make an educated decision.


I suggest you go for lead. The first conversion is doomed to be full of mistakes and things that could be done better, so don't even try to go for perfect. When you've managed to get a bike that rolls (even if it turns slow, clumsy and with a lousy range), you have at least succeeded and can either start planning improvements or simply aim for a new, and better, project.

That's why I'm planning to turn a S-10 to a lead-sled as my first try. It won't be good, it definitely won't be perfect, but it's gonna run and it's next to impossible to fuck up since I won't have to do any heavy modifications to the vehicle (well, except from ripping out the ICE and put a motor in). For my next trick, I'm thinking either something sporty (Lotus?) or a 4WD with two motors (one front and one rear, sounds like an interesting approach). By then I hope the Lithium prices has dropped too.

But first I have to start (and finish, of course) my first conversion and I'm going to keep it as simple as possible because it will take a lot of time as it is. Everything takes a LOT of time first time you do it and the more you complicate things, the bigger the risk that you'll screw up bad. So don't.


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