DIY Electric Car Forums banner
21 - 40 of 49 Posts

·
Registered
Joined
·
112 Posts
Discussion Starter · #21 ·
Better yet, go get a used fork lift motor like I did. Less than $200 for bearings and brushes and paint....
very interesting! 200$ for a forklift motor?

can you tell me how I can shop for one that will be good for my needs
according to the previous thread 100-130hp peak would be perfect

Seriously I really thought a 40kw motor would do the job very well since the torque was instant... I wanted a smaller motor for better efficency and less power used...

thank you for all your help I think I will go with a forklift motor + soliton1
 

·
Registered
Joined
·
1,700 Posts
very interesting! 200$ for a forklift motor?

can you tell me how I can shop for one that will be good for my needs
according to the previous thread 100-130hp peak would be perfect

Seriously I really thought a 40kw motor would do the job very well since the torque was instant... I wanted a smaller motor for better efficency and less power used...

thank you for all your help I think I will go with a forklift motor + soliton1
Please make sure and start a build thread!

As far as your battery pack is concerned, if you do not want to be concerned with power or performance and are more focused on cost and cycle life....Thundersky lithiums are the way to go....

You need a usable range of about 60miles per day (500km/5 = 100km=60m)...since you shouldnt ever drive your pack down to zero, except in an emergency, 80% should be your daily limit, and that requires a total 75 mile range . @300wh/mile that equals 22.5kwh pack...

A 144V pack of Thundersky Lithium 160AH cells = 23kwh would be the choice... 45 cells are required @ 200$ eachUSD = 9000$USD and total pack weight = 556lbs (hopefully you will remove enough weight from the vehicle to keep this added weight neutral)

3C (3 x 160AH) from the batteries would give you peak continuous power of 480A @ 144V = 69kw or 93hp...this should be enough for a simple commuter conversion...while keeping cycle life healthy.
 

·
Registered
Joined
·
1,626 Posts
... I wanted a smaller motor for better efficency and less power used...

At high torque a bigger motor will have more efficiency because it have less resitance inside bigger copper bar and use less Amps for the same torque!!

Watch some graph of warp 9 vs warp 11 motor.
 

·
Registered
Joined
·
2,217 Posts
"Less amps for the same torque" has nothing to do with efficiency. All that means is less rpm for the same voltage. This is just a trade-off and neutral by itself. Lets look at the published efficiency graphs for the WarP 9 and WarP 11 motors...

WarP 9


WarP 11


The 9 inch appears to be 88% efficient at 300 amps while the 11 inch appears to be only 87% efficient. The graphs for the 9 don't go past 350 amps but you can clearly see how pushing the 11 up into higher amp ranges causes a drop in efficiency. I expect the drop off will be even a little worse for the 9 and worse still for the 7. Unless you are racing this is not where you want to maximize efficiency anyway. For a street EV you want to focus on efficiency at slightly over the motor currents you expect at cruising speeds. Remember that motor currents are greater than battery currents at less than full throttle, so I would look at efficiency at 150 to 300 motor amps, the high end for low voltage EVs and the low end for EVs using high voltage motors and battery packs.
 

·
Registered
Joined
·
181 Posts
I think that torque is actually very important for efficiency.
You can think of power as acceleration while torque is range.
Consider the case of W9 vs W11. Their only difference is not the ammount of amps they handle as both seem to be rated for 225A but torque and respectively rpm whereby W11 has 4000rpm at 144V vs 6000 for W9.
If you consider normal city driving, you rarely need top speed and the associated with it top motor rpm. To accelerate to a given speed what is important is that motor develops a given torque.
W11 will achieve that torque with less amps vs W9 hence overall its battery will last longer. What is more, as W11's rpm are less, on average it will work at higher voltages meaning again less amps and less stress on the other components. Hence added motor weight that produces torque in fact pays for itself by prolonging range.
The 88% efficiency at 300A is highly unlikely though - it is more like 82-84% but of course this is a biased opinion :)
 

·
Registered
Joined
·
2,217 Posts
I think that torque is actually very important for efficiency.
No, torque is just one part of power in a motor.

HP = torque * rpm / 5252

Look at the curves I posted, the 11 makes a lot more torque per amp but at a lower rpm. The efficiency of the 2 motors is similar. The gears in your transmission also turn less torque at a higher rpm into more torque at a lower rpm.
 

·
Registered
Joined
·
181 Posts
OK, maybe using the word efficiency was a poor choice.
Indeed electrical efficiency of the motor does not depend on torque (at least not directly).
What I wanted to say is that a motor with higher torque (but same power) uses the battery more efficiently and range with W11 will be more than with W9.
 

·
Registered
Joined
·
3,218 Posts
I am not 100% set with the build. I just take the poors and cons and I know the BLDC is not as powerful. I am not looking for power, but reliability. Maintenance free with a unmatch durability.

I know soliton1 has all that. I doupt any brushed motors can handle the winters with the insane amounts of sodium here. Or just survive for 5 seasons unless it is really really well isolated and not mentioning the maintenance of the brushes...
I think you might be overestimating the amount (and difficulty) of brush maintenance here. If the average power delivered by the motor is around its 1 hour rating then it is likely the brushes on a typical forklift/EV-size series DC motor will outlast the donor car... maybe even a couple donor cars.

As for surviving road-salting (though what do I know about that, being in sunny Florida?!), if you use a blower band on the motor you not only will keep it cooler, especially in stop-and-go traffic, but also prevent incidental water spray, dirt, rocks and, yes, salt from getting into it.

BLDC is pretty much a permanent magnet synchronous motor, or PMSM (I really dislike the term "BLDC" precisely because it is so misleading). So you need an inverter to drive a BLDC motor, just like with an AC induction motor, and since inverters are much more complex than brushed DC controllers they must be less reliable, even if build and component quality are otherwise the same!

A BLDC motor does have very high efficiency, but it requires hundreds of dollars worth of rare earth magnets to achieve. This has the unwelcome bonus of making the motor much more sensitive to damage from heat and/or pumping too much current through the stator. Oh yes, overloading a BLDC motor can demagnetize the magnets, typically manifested as a progressive loss of torque at a given stator current.

The advantage a BLDC motor has over an ACIM is the magnets in the rotors make it much easier to determine the rotor's position in space - and therefore calculate the current vector for the stator - without resorting to an encoder. This may be advantageous in RC applications, but it is of marginal utility in an EV. Personally, I'd rather go with ACIM.

I know nothing about the system that Dave Kois has, but it sure looks like the generic Chinese forklift/NEV stuff that has been floating around the internet for years now. Please note that the power rating quoted for these things is ALWAYS a short-term PEAK - the continuous rating is often less than half, and sometimes as little as 1/4, the peak power rating so loudly trumpeted in the specs. Even keeping the controller cool won't help since the real Achilles heel is the ripple current rating of the input capacitors (it's what limits the Zilla Z1K, for example, to 300A continuous, despite being a water-cooled controller).

I personally think that BLDC is a dead-end technology for EVs - much more so than brushed DC. ACIM will be the preferred technology in the future, it's just that the future ain't quite here (getting closer, though)...
 

·
Registered
Joined
·
112 Posts
Discussion Starter · #29 ·
Please make sure and start a build thread!

As far as your battery pack is concerned, if you do not want to be concerned with power or performance and are more focused on cost and cycle life....Thundersky lithiums are the way to go....

You need a usable range of about 60miles per day (500km/5 = 100km=60m)...since you shouldnt ever drive your pack down to zero, except in an emergency, 80% should be your daily limit, and that requires a total 75 mile range . @300wh/mile that equals 22.5kwh pack...

A 144V pack of Thundersky Lithium 160AH cells = 23kwh would be the choice... 45 cells are required @ 200$ eachUSD = 9000$USD and total pack weight = 556lbs (hopefully you will remove enough weight from the vehicle to keep this added weight neutral)

3C (3 x 160AH) from the batteries would give you peak continuous power of 480A @ 144V = 69kw or 93hp...this should be enough for a simple commuter conversion...while keeping cycle life healthy.
I did start a build thread but no one helps... Maybe Im too boring lol
 

·
Registered
Joined
·
2,217 Posts
What I wanted to say is that a motor with higher torque (but same power) uses the battery more efficiently and range with W11 will be more than with W9.
The motor "with higher torque (but same power)" is turning a lower rpm.

Look at the graphs. The 11 is most efficient at about 260 amps, the 9 at about 240 amps. At 200 motor amps the 9 is more efficient than the 11 according to the numbers posted by the manufacturer.

Racing does step the motor size up because efficiency at 1000 and even 2000 amps becomes important. For the street bigger is not necessarily better. To small and efficiency suffers and the motor is likely to overheat. To large and efficiency in the most used power levels suffers a few percent most of the time while the efficiency gains at higher loads are only seen a small percentage of operating time.
 

·
Admin: 'one of many'
Joined
·
4,838 Posts
very interesting! 200$ for a forklift motor?

can you tell me how I can shop for one that will be good for my needs
according to the previous thread 100-130hp peak would be perfect
I found my 12" motor from a milk float for £100 on Ebay and my 11" motor, complete with the axle and wheels from a Still R30/60 forklift for £150 as a direct link from another member here. My 9" motor and 7" motor were free from other members of the forum helping me out.

Finding motors is a matter of persistence and luck, like buses you will have nothing for months and then several come along at once:D.
You should try to find somewhere local that breaks forklifts or plant machinery. Also get to know your local scrap metal yard as sometimes complete forklifts get weighed in for scrap.
You can also look at plant sales to find old electric forklifts for sale. You can arrange a friendly three way trans action with your scrap yard so that you buy it, they collect it, you get the motor and they then give you the scrap value of the rest of the truck.

Also if there are EV guys in your area they may already have contacts and look outs for suitable motors.

Sometimes just asking friends, at work, etc if anyone knows of a local factory with an old forklift or other electric factory truck that is wasting away in a corner might get you some leads. Sometimes they just want it out the way for less then the cost to them of transporting it away.


thank you for all your help I think I will go with a forklift motor + soliton1
If only I could afford the Soliton1...:rolleyes:
My budget is tight so I am going for the Paul and Sabrina Open Revolt kit.:)


I did start a build thread but no one helps... Maybe Im too boring lol
Bring it back up with some photos and questions as you go along. Sometimes there is just nothing to say back yet. Look at the way my threads started, chat and photos with no direction for a while and then it started to some together.
 

·
Registered
Joined
·
112 Posts
Discussion Starter · #32 ·
I agree, but before posting pictures I need help with my setup

this is my knowledge of the circuit I need help connecting the Charger and the BMS system, I have no clue how

 

·
Admin: 'one of many'
Joined
·
4,838 Posts
I was about to say you made a mistake but you have found it yourself.:)

It looks about right the way you have it there. Not sure about BMS, I think each cell would have a small BMS board across the pos and neg terminals.
 

·
Registered
Joined
·
112 Posts
Discussion Starter · #35 ·
I was about to say you made a mistake but you have found it yourself.:)

It looks about right the way you have it there. Not sure about BMS, I think each cell would have a small BMS board across the pos and neg terminals.
yeah but arent the minibms suppose to be linked to a slave board then linked to a masterboard?
 

·
Registered
Joined
·
2,217 Posts
The fixed schematic looks correct. I would like to add that a you should include an input fuse to the DC to DC converter. This needs to be something properly rated for the DC voltage and for slightly more amps than the DC to DC peak input amps. I generally use an ABC fuse (ceramic 1/4" by 1-1/4"). If your DC to DC is actually an AC to DC converter that happens to work on DC (like the Iota DLS models) you cannot rely on the built in fuse as it will almost certainly only be rated for high AC voltage.

As for the BMS, I recommend installing individual boards at each cell and then wiring the isolated signal loop back to the master. I don't recommend wiring all the cells to a slave board unless you can place a fuse in each wire near the cell. Just think about what could happen if you short a couple of those wires between different cells and the slave board.
 

·
Registered
Joined
·
112 Posts
Discussion Starter · #37 ·
The fixed schematic looks correct. I would like to add that a you should include an input fuse to the DC to DC converter. This needs to be something properly rated for the DC voltage and for slightly more amps than the DC to DC peak input amps. I generally use an ABC fuse (ceramic 1/4" by 1-1/4"). If your DC to DC is actually an AC to DC converter that happens to work on DC (like the Iota DLS models) you cannot rely on the built in fuse as it will almost certainly only be rated for high AC voltage.

As for the BMS, I recommend installing individual boards at each cell and then wiring the isolated signal loop back to the master. I don't recommend wiring all the cells to a slave board unless you can place a fuse in each wire near the cell. Just think about what could happen if you short a couple of those wires between different cells and the slave board.
very interesting but I am still not clear on how to make the connection
can you post me link of what you are explaning to me or can you draw me a plan and tell me which is which???

mini bms to a master board? but I thought master boards was only 16 slots
 

·
Registered
Joined
·
2,217 Posts
You need to go here and read about the miniBMS. I recommend the "distributed" version, not the "centralized" version. If the central boards are used you really need a fuse in each wire going from Lithium pack to the central boards, located at the cells.

In the picture showing the "distributed" boards you can see a black wire going from one board to the next. This is the isolated loop that goes back to the "head end board" (shown in the larger picture at the top of the page.) The rest of the connections on the head end board are part of the vehicles 12 volt system. The head end board is built into the centralized boards.

The info on the link I gave is invaluable for understanding and installing the miniBMS. My system is a hybrid, using the head end board from the miniBMS system and cell modules from EVworks.
 

·
Registered
Joined
·
1,760 Posts
It's probably a good idea to add a small 12 Volt battery on the secondary side of the DC/DC too, otherwise your car will die instantly if the DC/DC shuts down because of overload or overtemp or, of course, if it breaks.

Even a temporary overload that makes the DC/DC go into brown out will make the Soliton shut down to protect itself, which will require a restart (ignition off/on) to clear. Might not be so fun if it happens in rush hour.

A DC/DC that provides ~13.5 Volt and a small MC-battery on a few Ah will save you from this and will provide you with power enough to limp home if you're conservative with headlights etc.
 

·
Registered
Joined
·
112 Posts
Discussion Starter · #40 ·
Ok so a DC-DC conerter is unreliable? I mean why would I need a 12v battery? anyways if its recommended I will buy one

also about bms I will go with the distributed

still unsure how to connect those

pos to neg on every battery and a little wire to jump from 1 minibms module to the other one

after they are all connected does that go to a centralised masterboard?

how is the charger going to stop if no wires are connected to the charger? The bms will distribute the current untill the pack reach maximum voltage and the charger shutsoff when it notices full charge?

or am I still lost?
 
21 - 40 of 49 Posts
Top