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Re: An Intuitive Approach to Fissiks and Mechanics

This conversation is probably better had elsewhere, as it's not very strongly related to finding a good motor.

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Apologies, I was trying to work out my battery capacity to choose the correct voltage DC motor for my requirements. I hope this is Ok

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Re: An Intuitive Approach to Fissiks and Mechanics

Apologies, I was trying to work out my battery capacity to choose the correct voltage DC motor for my requirements. I hope this is Ok

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I meant the discussion over which units to use.

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My first post here!
I recently became fascinated with the thought of an EV conversion on an old car with a non-running ICE.

Let me follow J_D above and state my goals and facts and, hopefully, you can guide me to what motor should I look for as I don't know much about them, so don't want to make a stupid first decision. For example, I was looking at what looked like a candidate motor only to find that it is a treadmill motor. 🙂

My objective is to keep this a cheap project. Basically, cheaper or close to rebuilding an ICE. The vehicle would be a fun, occasional vehicle, no winter use planned.

The facts/objectives:
Car weight: ~900kg
Original horsepower: 60hp
Transmission: classic 5-speed manual with clutch. (Not needing a clutch would probably save the work on restoring that system in a vehicle that has been sitting a while.)
Range target: 40-50km (to get me anywhere in the city and back)
Top speed: 120-130 km/h (highway speed limit is 100-110 and sometimes you need to get the hell out of the way - although I know the acceleration at the high end won't be there)
0-100 km/h: 10 secs (more important would be the 0-60 km/h for those red light starts!)

So, I know I'm looking for a cheap forklift DC Series wound motor, but what is the volt and amp range I should aim for? Will any 24V-48V do? I realize it's the controller where the magic happens though.
Is there a reasonably priced battery pack these days or to keep this cheap, should I stick to classic 12V auto batteries? I can probably stuff 8-10 of those easily.

Thank you very much!
 

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Lead is dead - with lead actual ranges were less than 20 miles and 2 years for life
For your needs a Chevy Volt pack would be great - I paid $1800US for mine

Motors - most here are 48v
But you will be running them higher
I'm running 340 volt - but that is excessive - 150v is OK - much below and your top speed will suffer

This is my "Device"

https://www.diyelectriccar.com/foru...dubious-device-44370p15.html?highlight=duncan
 

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So, 48V motor is what I need?
Series-wound motors don't really have voltage limits. They just have the voltage that the truck was run at. I'm skeptical if there's even a difference between a motor from a 24v lift and a 48v lift. I dunno, maybe there is.

Either way you'll be running them at several multiples of their original voltage.

You need a motor the right size. With a light car like that you might pull off a 9" motor, but 11" is probably better. Generally anything that diameter will be the right ballpark size.

It sounds like battery will be the "not cheap" part of my or any project.
How much of a battery pack do I need?
You have quite modest battery requirements.

You only want 30 mile range. For your light car, perhaps 250 watt-hours/mile, so, 7500 watt-hours. That's incredibly small, you won't find anything that small in an OEM EV.

A Chevy Volt pack is quite small, and even it is 16,000 watt-hours. I'd go with one of those.
 

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You have quite modest battery requirements.

You only want 30 mile range. For your light car, perhaps 250 watt-hours/mile, so, 7500 watt-hours. That's incredibly small, you won't find anything that small in an OEM EV.
True, but you will find that in the lower-capacity plug-in hybrids. The Volt is a higher-capacity plug-in hybrid... like the Chrysler Pacifica Hybrid and Mitsubishi Outlander PHEV.

Perhaps more importantly, all modern EVs and hybrids use higher voltage than will likely be used with a brushed DC motor. If you use, for instance, one-third of a 360 V EV pack to get 120 V, you have one-third of the energy capacity... that's only 8 kWh for an early Leaf.
 

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Thank you.
I see a few hybrid battery packs from Prius and Camry available. So, those would be suitable? And I'm looking for around 8kWh?
Looks like Prius Gen 1 is only 1.6kWh and Gen 2 is 4.4Kwh.
And are controllers and BMS hard to find/match for those?

P.S. Please let me know if I should start a thread in the battery section instead of here.
 

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I see a few hybrid battery packs from Prius and Camry available. So, those would be suitable? And I'm looking for around 8kWh?
Looks like Prius Gen 1 is only 1.6kWh and Gen 2 is 4.4Kwh.
And are controllers and BMS hard to find/match for those?

P.S. Please let me know if I should start a thread in the battery section instead of here.
Yes, this is a battery question, not a motor question, unless you are determined to use the motor, controller, and battery all from the same donor.

And the answer to that battery question is that non-plug-in hybrid batteries are too small, but plug-in hybrid (Prius Prime, Chevrolet Volt, Chrysler Pacifica, Mitsubishi Outlander PHEV, etc) batteries are around the target energy capacity... as long as you want 360 volts.
 

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Thank you.
I see a few hybrid battery packs from Prius and Camry available. So, those would be suitable? And I'm looking for around 8kWh?
Looks like Prius Gen 1 is only 1.6kWh and Gen 2 is 4.4Kwh.
And are controllers and BMS hard to find/match for those?

P.S. Please let me know if I should start a thread in the battery section instead of here.
I would be looking at more than 8 kWh

I have 14 kWh in an 800 kg car - and that gives me a 50 km range at 100 kph

Admittedly my car is aerodynamically challenged!
 

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Hello Friends,

I am just testing this induction motor with its controler. Maybe somebody detect this. So far it works ok, but somehow I dont like that fact that it must have electronic brake pedal. I am looking for somebody having this kit and was able to connect to ECU via its J1949 ,,and fine tune its drastic regenerative breaking.., It is bit technical question but maybe somebody else will be interested for this. It is 48-60V system 12 000Rpm / 1000A peak. Thank you
 

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Hi suk,

Not bad :) Here's a couple of comments. Refer back to your #1 post for quote context.



Not necessarily. Many 36V motors work out well for guys on 72 or 96V systems, some even higher. That usually requires advance (shifting the brush position).



Unless you go way overboard, I doubt you need to worry about a few motor pounds subtracting from your range.



HP is HP ;) Electric motors and gas engines are rated differently w/r/t HP. And they have different torque curves. But one HP from an electric motor shaft is exactly the same as one HP from a gas engine shaft at the same RPM :)

Regards,

major
Hi Major,
One thing that I have a hard time to understand. Many folks on this site are suggesting to use a forklift DC motor to replace the original combustion engine. But as you say, an electrical motor HP and a combustion engine HP is the same... So, if I want for instance replace a 100 HP combustion engine and look at the 100 HP electrical motors outthere, they are a lot bigger than the typical forklift DC motors. And for some reason, these forklift motors are not showing the amount of HP they are providing on any nameplates that I looked at. So, how can you size a "good" forklift DC motor to fit your expected output power?

Thanks,
eSharo
 

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Hi Major,
One thing that I have a hard time to understand. Many folks on this site are suggesting to use a forklift DC motor to replace the original combustion engine. But as you say, an electrical motor HP and a combustion engine HP is the same... So, if I want for instance replace a 100 HP combustion engine and look at the 100 HP electrical motors outthere, they are a lot bigger than the typical forklift DC motors. And for some reason, these forklift motors are not showing the amount of HP they are providing on any nameplates that I looked at. So, how can you size a "good" forklift DC motor to fit your expected output power?

Thanks,
eSharo
The motor is a device to convert electrical power into mechanical power
The more power you "feed" it the more mechanical power is produced

So the power that can be produced is determined by the controller - not the motor

A motor can produce a LOT of power if its only for a short period

Additionally

Power = Torque x Speed

Torque is (roughly) proportional to Current - as is HEAT

So if you are going at twice the rpm THEN you can produce double the power for the same amount of heat
AND if the motor is cooled by a fan on the motor shaft - THEN you can cool and remove more heat

The result is that a Fork lift motor with a 10 kW "rating" at 1400 rpm will have about the same heat buildup at
4,000 rpm and 50 kW
That would be the "1 hour rating"
Most cars will "do the speed limit" at about half of that (25 kW) - so they can't pull 50 kW continuously anyway

Short term power - for acceleration - can be much higher!

I am feeding my 10 kW Hitachi motor with 400 kW for a short period
 

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The peak HP may be the same, but the torque curve vs RPM is totally different between a motor and an engine.

In both, the force at the tires at a given wheel speed is what matters. It has to at least balance rolling resistance, drag, and powertrain losses.

There's no magic - the wheel HP curves for an ICE and an electric motor vehicle have to cross over at a given speed on the graph, or the electric has to at least equal or exceed the ICE WHEEL torque at that given speed.

In a motor, you can alter that output for short periods, as Duncan has said. When you need it...at low speed for short periods of time. In an ICE you have to slip the clutch to multiply torque....for short periods of time, also.
 

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Thanks a lot guys.

Waiting for your replies, I educated myself in parallel and found out many interesting things on the subject on this forum and on the net.

What I understand better now is that the required starting torque for a DC motor is not an issue since the lower the RPM, the higher the torque for a DC electrical motor.

My main concern now is the higher speed torque peaks required for say hill climbing or higher speed acceleration. For a given voltage supply, the generated HP will be the same so that for higher RPM, I will get a lower available torque. But on the other hand, I can configure the controller to supply higher voltage to generate higher HPs (raise the "speed-torque curve") therefore, higher torque for a given RPM. But in this situation, the dissipated heat may be a problem but as Ducan said, a fan installed on the motor shaft would help a lot.

I figure out that I will not be able to anticipate completely the behavior of a given DC motor to replace my current engine while designing my system but as a general rule, I will choose the highest possible HP rated motor available with the ability to install a fan on its shaft if not already equipped as such. I will also plan for a controller that will allow to supply higher voltages (higher than the nominal voltage of the motor) at higher RPMs. Since I will keep the current transmission in the vehicle, my sweet spot RPM for a 100 KMH speed will be around 2000 RPM as it is now. So, I'll have to keep a fairly good acceleration (torque) beyond this RPM until say about 2500 RPM. The rest of the story will be a try and "error" workbench test plan making sure that I will not let the motor to overheat not to damage it.

Any other comment from the community would be welcome!

Thanks!
eSharo.
 

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Thanks a lot guys.

Waiting for your replies, I educated myself in parallel and found out many interesting things on the subject on this forum and on the net.

What I understand better now is that the required starting torque for a DC motor is not an issue since the lower the RPM, the higher the torque for a DC electrical motor.

My main concern now is the higher speed torque peaks required for say hill climbing or higher speed acceleration. For a given voltage supply, the generated HP will be the same so that for higher RPM, I will get a lower available torque. But on the other hand, I can configure the controller to supply higher voltage to generate higher HPs (raise the "speed-torque curve") therefore, higher torque for a given RPM. But in this situation, the dissipated heat may be a problem but as Ducan said, a fan installed on the motor shaft would help a lot.

I figure out that I will not be able to anticipate completely the behavior of a given DC motor to replace my current engine while designing my system but as a general rule, I will choose the highest possible HP rated motor available with the ability to install a fan on its shaft if not already equipped as such. I will also plan for a controller that will allow to supply higher voltages (higher than the nominal voltage of the motor) at higher RPMs. Since I will keep the current transmission in the vehicle, my sweet spot RPM for a 100 KMH speed will be around 2000 RPM as it is now. So, I'll have to keep a fairly good acceleration (torque) beyond this RPM until say about 2500 RPM. The rest of the story will be a try and "error" workbench test plan making sure that I will not let the motor to overheat not to damage it.

Any other comment from the community would be welcome!

Thanks!
eSharo.
Kind of!!
But its better if you think about Current = Torque
Your controller will alter the Voltage it feeds to the motor in order to deliver the demanded current - up until 100% when the Motor voltage = Battery voltage

Rather than
the lower the RPM, the higher the torque for a DC electrical motor
In most cases you have the same torque up until you don't have enough voltage to sustain that current THEN as rpms rise the current and the torque both drop

Most motors will survive a lot more than 2500 rpm - and its better to operate at higher rpms - also gearing for 100 kph and 2000rpm is difficult!!!
 

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Thanks again Duncan. I got you... But regarding the 100 KMH at 2000 RPM, there is nothing I can do since it is the current built in mechanism characteristics. But I will try to find a controller to have the ability to cope with it and, as I said before, provide a battery pack that will supply higher voltage than the nominal voltage of the motor. This will leave the controller to adjust the voltage to cope with the torque (current) demand at higher RPMs. Sounds good?
 
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