Yet another CRF 250 Build but its my first so... ;)

[DonCox]

I don't want to bad mouth Eon Lithium , but we have bought a few batteries from them, and have not been real happy. Bob knows Raymond there at EON Lithium real well, and has one of his batteries, and I put one in one of my customers bikes, and were not real keen on them. The battery you are looking at is with Samsung 50S cells, yes if you were trail riding, it would be OK, but 300A max will be weak, and if your battery is over 300A you want a QS10 Anti spark output connector. The Amorge folks can and will build to your spec. Cells are an expensive part of the equation. The video I sent you gives some pricing, but roughly the Molicel P42A, (4200mah 45AH)is about $4.50 a cell, Lishen LR2170LA(economy cell) will give you 4000mah and 35AH, but with some heat. The Samsung 50S about the same price as the Molicel P42A, but 5000mah and 45ah, but create more heat ( higher resistance). Then there are the Molicel P45B, and the P50, which are all better. P45B is what the Stark is using, and more expensive, and then the P50B which is better , but way more expensive. We have put 20S12P in the Honda frame, if you are designing for and with a quick change battery in mind this is the good size. If you could get a 20S14S or 16S battery in a CRF frame with the Molicel P45B or P50B cells you would have the range and the Power you need. You want the 40A charge BMS , but you need to have the power side Open Discharge, or no BMS control. ( to reduce heat in the battery box, since the controller has low voltage control. The battery is the most complicated part of the build.

 

[Dave Daum]

Thank you Don for all of this great information. I'll digest this and write a battery build specification for the bike I'm building.

 

[fmxxx666]

You want the 40A charge BMS , but you need to have the power side Open Discharge, or no BMS control. ( to reduce heat in the battery box, since the controller has low voltage control. The battery is the most complicated part of the build.

Hi @DonCox , do you know if its possible to ask Amorge for a 40A charge BMS and open Discharge on their batterys?

 

[DonCox]

Yes you can ask for it and they will do both. I just received a battery from them, with Open discharge, but i did not spec 40A Discharge, so it only has 20A charge. Here are a couple of pictures of the KTM battery I just got. This is a 20S12P Molicel P42A cells, Open Discharge, and Charge only Smart BMS. The Idea is to quick change out of the left side. I have to redirect the radiator bottom output to go straight up

 

[Dave Daum]

I don't want to bad mouth Eon Lithium , but we have bought a few batteries from them, and have not been real happy. Bob knows Raymond there at EON Lithium real well, and has one of his batteries, and I put one in one of my customers bikes, and were not real keen on them. The battery you are looking at is with Samsung 50S cells, yes if you were trail riding, it would be OK, but 300A max will be weak, and if your battery is over 300A you want a QS10 Anti spark output connector. The Amorge folks can and will build to your spec. Cells are an expensive part of the equation. The video I sent you gives some pricing, but roughly the Molicel P42A, (4200mah 45AH)is about $4.50 a cell, Lishen LR2170LA(economy cell) will give you 4000mah and 35AH, but with some heat. The Samsung 50S about the same price as the Molicel P42A, but 5000mah and 45ah, but create more heat ( higher resistance). Then there are the Molicel P45B, and the P50, which are all better. P45B is what the Stark is using, and more expensive, and then the P50B which is better , but way more expensive. We have put 20S12P in the Honda frame, if you are designing for and with a quick change battery in mind this is the good size. If you could get a 20S14S or 16S battery in a CRF frame with the Molicel P45B or P50B cells you would have the range and the Power you need. You want the 40A charge BMS , but you need to have the power side Open Discharge, or no BMS control. ( to reduce heat in the battery box, since the controller has low voltage control. The battery is the most complicated part of the build.

Thank you Don for all the wonderful information. Now I have to figure out how to get the most power and range into the fairly small space I have to work with. It is going to take some creative fabrication. Looks like I'll need to reduce the size of the shock tower cross member and the wishbone. Trying to get a 6.25 x 8.25 x 13.00 battery case in this s.all space is challenging. Hoping to get 20S 12p.

 

[bananu7]

I hope you weld in some reinforcements if you cut out as much as you're drawing here.

 

[Dave Daum]

The plan is to remove as little material as possible. Once the battery arrives I'll carefully fit it to the bike. I want to avoid welding on the aluminum chassis. My fear is the welding will change the heat treatment and soften the aluminum.

 

[fmxxx666]

Trying to get a 6.25 x 8.25 x 13.00 battery case in this s.all space is challenging.

this sizes sound exactly like the Electro & Co eg. eonlithium.com 76v 48ah battery.
Also tried to test fit that in the 2009 CRF 250 Frame but zero chance would have to cut away way too much from the frame.
so 72v will be enough for me I will see what amorge is able to do maybe also an "irregular shape batt" they have done these before:





something like this so it goes down in front of the Motor and uses that space as well:

 

[DonCox]

I have a 6.25x8.25x13" Amorge in a 2005 450CRF frame with only slight mods. I heard that the 250 frame is narrower

 

[bayodome]

There goes the structural integrity of your frame. NEVER cut an MX frame that you are planning to use for MX. Please DO NOT jump this thing.

 

[fmxxx666]

@bayodome I guess we all agree on that one

we are just fighting for a few milimeters more to squeeze in the maximum power otherwise we wouldn’t be able to jump anything anyways if we have to flintstone that thing

 

[Dave Daum]

I'm going to gently remove as little material as possible. If the material removal causes any strength concerns, I plan to CNC machine and weld replacement pieces. I'll post images as we progress with the project.

 

[bayodome]

I'm going to gently remove as little material as possible. If the material removal causes any strength concerns, I plan to CNC machine and weld replacement pieces. I'll post images as we progress with the project.

Amorge can build a battery to your specs, or very close, to fit the frame as is. Why ruin the frame's structural integrity when you don't have to? If you're doing it to achieve 3 or 4 more ah, damaging the frame is not worth it. It looks like you're setting up the battery to be quickly removable from the top. That's exactly what I did with my YZ250F conversion.

I use a Chi Battery Systems 72v 51ah Gladiator Max (originally designed for a Light Bee), and it fits just fine within my frame and easily slides out from the top. It's also capable of 420a continuous and 540a peak. If you want more range, do the same battery or equivalent (Amorge could come close to those specs but for significantly cheaper, they just were really an option when I built mine about 1.5 years ago), or get two and there's your increased range. But I stress again... DO NOT CUT THE FRAME. Especially if you're going to use the bike for MX!!

 

[DonCox]

I'm going to gently remove as little material as possible. If the material removal causes any strength concerns, I plan to CNC machine and weld replacement pieces. I'll post images as we progress with the project.

Dave, Bayodome has some valid comments, and some good ideas. I agree with not weakening the frames whenever possible. I think these cuts are minimal. But they do compromise the frames strength. But since you have a clean slate, lets look at his choices. On his YZ250F ebike, he is using the CHI 72V Gladiator battery. The company Chi makes one of the few aftermarket batteries with fusible links ( similar to Tesla, Alta, and Stark) and that is a great feature. But the shape of the battery is a key element in your build. 6 x 5.7 x 16.5" should fit without any mods to the frame. They are a bit more pricey than the Amorge. But I think Amorge can build to almost any size. So lets mock-up a battery of that shape and see if it will work. Here is a picture of Bayodome's YZ with that battery. And as Bayodome also commented on, you might want to build in Quick Change option too. I was at the Worcs Race here this last weekend, and my friend Steve was racing his YZ250F "Electra". It was an enduro, 55 minutes Races, with the size battery we all are using (20S12P Molicel P42A cells, and that is the same for the CHI battery) He got 4 laps (good power at 7 minute laps) of the 7. He does not have a quick change yet, but that is my next week project to install and design the Quick Change into a 2014 YZ250F . I am using the battery out of the Honda for the YZ250F (IMG6593). This battery slips right into The 2014 YZ250F easily. With parts from XEMX1.com for the modification of the plastics for a quick change battery system.

 

[bayodome]

Great points all around, Don, as always!

I'll take some more with the seat off so you can see what I did. The Yamaha is a bit unique with the under-the-seat gas cap, so I took advantage of that, but it would likely be easier to setup the quick change option on a bike with traditional gas tank orientation like your Honda.

Here's some more detailed shots of the completed build:

 

[Dave Daum]

Hello Don and Bayodome! You both have contributed a wealth of knowledge and experience. Bayodome brought up some valid points. The 5.7 x 6.0 x 17.00+/_ form factor is very interesting. Your YZ is a very clean build. I'm curious, Is there enough clearance in front of the battery to fit the EM-260 controller? And, would this be a good location to help keep it cool? I'd love to here your thoughts...

Is this the CHI Battery Bayodome referred to: Gladiator 72 Touring S - 60ah Sur-Ron Battery

 

[bayodome]

Hello Don and Bayodome! You both have contributed a wealth of knowledge and experience. Bayodome brought up some valid points. The 5.7 x 6.0 x 17.00+/_ form factor is very interesting. Your YZ is a very clean build. I'm curious, Is there enough clearance in front of the battery to fit the EM-260 controller? And, would this be a good location to help keep it cool? I'd love to here your thoughts...

Is this the CHI Battery Bayodome referred to: Gladiator 72 Touring S - 60ah Sur-Ron Battery

Happy to help wherever I can. Don is the true guru here, whereas I have gained some practical knowledge through my own recent experiences... although I'm a lifelong MX enthusiast. As far as electronics go though, Don is the mon!

To answer your questions:

1) It may be possible to fit the EM260 controller in front of the battery on my build. However, the main reason I would not do that is heat. The battery, motor and the controller all generate heat when pushed. For MX, which is what I mostly do, I generally ride my bike at 350a continuous (off the bottom feels somewhere between a 350F and 450F, then drops to 250F level power as it winds up). In this setting, after about 15 to 20 minutes (about the max range/time I can get with this setup) all of the components have generated considerable heat. I've never taken the temp, but they're all hot to the touch.

I mention all of this because it means you would want to keep the controller and battery separated, if you're sticking with air cooled options. While the controller is under the seat on my build (thanks to the mounting bracket that Don built for me!), the heatsink is still fairly exposed to the air. One thing I have not gotten around to is attaching some cooling fins to the heatsink. That will also help manage heating issues.

I've seen some people mount their controllers in place of a left or right radiator. That is certainly a great location, although also off center, weight-wise.

2) No, but the Gladiator Touring 72v is a great option if you're simply looking for range. Their newest generation batteries (mine is an older version, that did not come with the metal casing) offer higher power output overall. The Touring has 300a continuous and 540a peak. This means to come close to achieving the power of my build, you'd be running at absolute maximum continuous power most of the time, therefore generating a lot of heat. BUT if you do want the range, it'd be awesome. When I ride trails on my build, I generally do it at about 150a and get around 20 miles, depending on the terrain. 60ah, would probably get you closer to 25 or 30 miles.

I use this battery (again, mine is an older model, but the specs are pretty much the same): Gladiator 72 Max - 51ah Sur-Ron Battery

 

[Dave Daum]

Thank you Don, Bayodome, and fmxxx666 for your encouraging words and concerns. I plan to use the CRFE for 1/2 motocross and 1/2 single track. Range is a big issue. I'd like to pump up the AH as much as possible. Power wise I'm happy with 30KW. I'll just ride it like my 125cc and 150cc two-smokes.

Configuration wise I'd like to use the otherwise dead space ahead of the shock and over the motor for additional cells. I'd also like to keep the weight as low and balanced as possible. Amorge will most likely be the source of supply for the battery. Below are specification taken from an Amorge 20S13P 72V 52AH 320AMP battery. I modified the Amorge specs to the best of my limited abilities. Would you guys be kind enough to review my battery specification (below) and mark up any changes that need to be made? Please redline as much as you see fit. Your guidance means the world to me! -- Dave


2010 thru 2013 CRFE Battery Case V1

 

[DonCox]

Dave, A couple of ideas. The shape of the battery you proposed will be difficult to fit. Bob Casper in his CRF 250 build built 2 separate batteries. 20S6P x 2 for multiple reasons. One to fit in the CRF frame, two for the battery heat, and three for faster charging. Now there could be space for 2 20S8P batteries, and all that is hard to layout until you get the motor and controller mounted. Heat is an issue. Now you are proposing to go with the X-9000, that can produce 500A at 72V nominal. To produce that current , your battery must be quite a bit larger. As Bayodome says, his nominal current is 350A, I run 300A normally, and occasionally the Sport button at 400A (I call it my "Push -to-Pass" button). Our 20S12P batteries should produce 540A, but I have found that with all this current there are more losses. The best you should see is about 90% of what they claim. That is why I am suggesting 20S16P (2 x 20S8P) . Now with P42A Molicels, that would give you 720A theoretically, about 650A actually. And at lower rates, trail riding, a lot more mileage. Now if you were to use the new Molicel P50B batteries, you will get about the same max current, but 20% more range for trail riding. ( but they cost a lot more.)
Now why 2 batteries? For one we turn off the Discharge BMS current control, (called Open discharge) to reduce BMS heat buildup in the battery, and we split them to allow faster charging. I use 2 15A chargers on my split battery. I have a 120V 3500W generator, another friend who does not have the split battery, has a larger 240 VAC 4004W generator for his 72V 30A charger. (much larger and heavier) You may have noticed that to charge the Stark, you need a big generator to produce 240V 20A. (4000W plus 240V)
Now to get that size battery into the bike is a challenge. I have the battery racks, and I make the battery shape to fit first. Here is a shape idea for 20S16P in 2 batteries. Here is aside shot of a 2005 crf, and then a picture of battery racks 12 long, 11 1/2-12"s, and then an idea of a battery shape

 

[Theo]

Bob Casper in his CRF 250 build built 2 separate batteries. 20S6P x 2 for multiple reasons. One to fit in the CRF frame, two for the battery heat

Now why 2 batteries? For one we turn off the Discharge BMS current control, (called Open discharge) to reduce BMS heat buildup in the battery

I like the idea to have more batteries to reduce heat, not only because of the possibility to turn off that Discharge BMS current control.
There is a concept used when calculating the cooling rate of cast parts, like cast iron: the modulus, or volume to heat exchanging surface ratio. If you have a cube having side length X, then its volume is X³ and the surface is 6X²; the volume to surface ratio is X/6. Another cube having a side 2X long will have a volume of 8X³ and a surface of 24X² [because (2X)³=8X³ and 6 • (2X²)=24X²], so the ratio becomes X/3, which is twice as big, so this cube will take more time to cool down. In general, the bigger the object, the bigger that ratio is.
This concept holds good for batteries, too, if you split a big battery into two smaller ones, you get extra heat exchanging surface, like in this picture where you get the two yellow surfaces to exchange more heat:

I actually think that it could be better if batteries of electric dirtbikes had some cavities to increase their surface, provided they would not get filled with mud.
(The same concept applies to biology, too: like a teacher told me, cells are small because they need a low volume to surface ratio in order to exchange nutrients etc. fast enough. I've also seen the same concept applied in other situations.)