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EKartGo Project

Posted: Aug 25 2020 10:31pm
by hallkbrdz
It's finally time to start documenting my build on this forum, and eventually with videos on YouTube. The goal for this build is to create a kart that is competitive with both of the local tracks karts. B&S 206, and TAG 100cc. Obviously the B&S is easier (and will allow for much longer runtimes), but the goal is at least a 18 minute runtime from the battery pack without charging. That's good for two races here at our short road track. I'm leaning heavily on the lessons learned by several others on here who have brazed the trail so to speak, chiefly Kohlme's.

The kart I am starting with is the one I raced in 2018. It's a GP Racing 2008 shifter kart model. Here, shown with the Honda 80cc engine.

Battery: The first thing to be built will be the battery. This will be composed of 420 Molicel INR-18650-P26A cells in a 42S10P arrangement. The reason for a higher voltage is to support 120v motors such that at the end of the pack use the minimum voltage is still above 120v. The battery case will include a GV200 contactor, fuses, as well as a low-amp switch to a Vicor VI-251-EW DC/DC converter (external).

Motor: This is not what I really want, but it's what I can get for now. I live in Oklahoma, and it's hot here. An air-cooled motor just isn't going to cut it. I need a motor that is liquid cooled to keep it reasonably cool, without it weighing a huge amount. So to start with I plan to use a Motenergy ME1302 for B&S 206 speeds, to be replaced with a much more powerful as well as lighter to-be-released DHX Machines model early next year for TAG speeds.

Controller: For now a Kelly KLS14401-8080IPS. It can handle the voltage, and has current capabilities that match well with what I am trying to do.

BMS: Orion2. I like the all in one design, plus great support being a US company product. It will be external to the battery, connected via a 55 pin Mil-Spec round plug, saving me money when building a second pack.

Motor Mount: Custom. Loosely based on the Honda motor-mount, but much longer to distribute the torque as well as to support the right-side radiator and controller.

Sprockets (initial - I have multiple axle sprockets already):
Motor: 428 15 tooth - middle of the range in regards to the rear
Axle: 50mm 30 tooth - should give a final speed of 80 Mph at the end of the "straight", about 7 Mph quicker than the TAGs

Display: Probably a Samsung tablet, connected via bluetooth running torque.

Charger: Offboard Elcon or TC 3Kw canbus regulated.

Obligatory starting photo, although all the ICE stuff has long been stripped off (anyone need a Honda 80cc expert motor?)

Re: EKartGo Project

Posted: Aug 26 2020 10:25am
by hallkbrdz
Battery construction...

Cells are here
Spacers are here
Busbar copper and plastic is now here
Nickel strips are here
KWeld - here tomorrow!

Plan diagrams below. Busbar construction will have the nickel strips first welded to the busbars and then the busbars will be welded to the cells. All busbars will be 0.032" in thickness, except for the skinny strip at the top which will be 0.08" to compensate. The two layers will be connected at the lower left with the busbars overlapping.

Case bottom is 0.25" aluminum to attach to the kart. Above that and all the sides is 0.125" UHMW-PE. The top (not shown in completed battery) is 0.25" to allow attachment. No worries about shorts with this arrangement.

Time to get cutting and welding this weekend.

Re: EKartGo Project

Posted: Sep 04 2020 9:29am
by hallkbrdz
I hate delays... but life happens...

I should have some photos and possibly video up this weekend of the start to the battery build. It’s unfortunately going slower than planed because of various things that seem to come up that need more attention.

In the mean time here is my electrical layout. This is with an Orion2 BMS and Kelly IPS controller.
Electrical SimpleBatt - Orion2.png
Electrical SimpleBatt - Orion2.png (270.34 KiB) Viewed 634 times

Re: EKartGo Project

Posted: Sep 04 2020 9:53pm
by hallkbrdz
Some progress on building the pack tonight. One layer's cells inserted and ready for the busbar and strips. One to go...
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IMG_20200904_214152_sm.jpg (188.24 KiB) Viewed 615 times

Re: EKartGo Project

Posted: Sep 05 2020 11:55am
by hallkbrdz
Second layer completed... So far 44.1 lbs (20 kg).

Now I need to drill and trim all the copper bus plates.
IMG_20200905_114623_sm.jpg (379.2 KiB) Viewed 603 times

Re: EKartGo Project

Posted: Sep 05 2020 1:22pm
by hallkbrdz
Raw footage time lapse of the current 42S10P battery pack. This is the second layer. It uses 420 new Molicel INR-18650-P26A cells that will be tied together with copper plate / nickel strip sandwiches.

Cells were measured and sorted into groups of 3.3v, 3.35v, 3.4v, 3.45v, 3.5v, 3.55v, and 3.6+v. This is to minimize the charge/discharge current rush when the cells are electrically connected in parallel. A small difference is not a problem. The three 3.3v cells and two duds (or not charged 1.1v cells) were not used. It always helps to have a few extra cells for this reason.

Then a plastic collar is added to reduce the chances of a positive terminal to negative body short when welded.

Then the cells are inserted into the cell holders in groups of 10. The copper plates will tie the negative and positive terminals together a pair at a time, alternating sides. The two layers will then be stacked and two of the plates physically connected together to make a ~174.3v battery (cells charged to 4.15v). Max discharge voltage will be ~126v (cells discharged to 3v).

Re: EKartGo Project

Posted: Sep 06 2020 8:09pm
by hallkbrdz
Set up the kwelder today. I have too much current - so I'll have to use thinner leads or a weaker battery.

One H8 AGM battery with about 760mm of 2GA copper leads is too much for the record... :)

Re: EKartGo Project

Posted: Sep 09 2020 8:49pm
by hallkbrdz
OK, battery setup sorted with the H8, now works great for the nickel to cell connections!

Resistance is Futile - However the nickel to copper bus bar assembly will have to wait a little bit. Both the "thin" 0.032 inch (0.8128mm) and 0.08 inch (2mm) copper plates to 0.2mm nickel are just a bit too much for my kweld setup to handle. I am taking spinningmagnet's suggestion and will build a resistance solder rig for that task.

Re: EKartGo Project

Posted: Sep 11 2020 8:51am
by hallkbrdz
So the stock KWeld spot welding tips are not going to work, especially on the thick bus bars, for the nickel to cell connections. I think the old STTOS line "bear skins and stone knives" applies here. The holes are 5/8" (roughly 8mm), and although I could make them larger, I'd rather retain more copper.
IMG_20200911_083616.jpg (456.11 KiB) Viewed 490 times
I starting considering various ways to make thinner probes, and then found this video. Easy construction, versatile probe size, etc. Plus cheap. :-)

I plan to try 6 AWG silicone covered copper wire (doubled or trippled up inside the tube) with 3/32" tungsten tips. I will just run the wire out of the "pen" and to the KWeld board. That will let me retain the same size lug as the OEM one for easy mounting, while also reducing the heat of the wire.

Re: EKartGo Project

Posted: Sep 11 2020 11:35am
by spinningmagnets
The kWeld is perfect for welding the nickel onto the cell-ends, but...To weld the nickel onto a thick copper bus-plate, I would recommend a 1500W RSU as a spot-welder. Surprisingly affordable and easy to make. Timing is not critical, so a simple foot-switch works well. I can mail you a 1500W transformer for the cost of postage on Monday, if you like. I have several I picked up for free.



Re: EKartGo Project

Posted: Sep 14 2020 12:51pm
by nuxland
Following :)

That Motenergy ME1302 does not like a lot of current. In my test with 100V I found out that 18kw-23kw is what it can work with.
Why did you not use the newer Motenergy ME1616 motor?
Your battery idea is great, I was thinking the similar for my 4th battery for 35kw peak system (would limit my sevcon for 35kw, because you do not need more to race). I would use samsung 40T 21700 cells in 28s12p configuration and I was thinking of adding extra 1cm high aluminium radiator on top of copper to get heat out of the cells from both ends.
What is the maximum current your pack will deliver? Just thinking why so thick copper 0,8mm if my conversion is correct.
Have you calculated what wire gauge you copper will be? I'm using 0,5mm copper in my 25560 A123 build and it 50mm2 when I multiply 0,5 to copper width between cells (10mm) and then again to 10 (cell paralel count).

Re: EKartGo Project

Posted: Sep 14 2020 2:43pm
by hallkbrdz

On the motor I decided on the ME1302 over the ME1616 due to a number of factors:

1. Our "local" kart club only has two classes now, B&S 206 and TAG 100cc. I will initially run with the 206 senior heavy group until I get a second battery built. For 206 I only expect to have to run at most 5.5-6 kW to be competitive. At that rate the battery should easily last all day with no charging required between sessions. For TAG rates I only expect to have to run at about 13-14 kW, which should still be possible with the ME1302, other than maybe in the peak of summer when it's too hot for me to race anyhow as I don't do well with a ~150 F / 65 C track temp in a kart suit.

2. Weight! Saving about 13 pounds (or 6 Kg) over the ME1616 is huge in extending battery life. Of course me losing 15 pounds or more would also help a lot! Slowly getting there...

3. It's temporary. I'm still waiting for the motor I really want (and thought I originally had bought on Ebay). DHX Machines (US based) is running behind schedule on their new "mass produced" motors due to you-know-what, but expects to have them available for purchase next spring. They will use the same cooling technique as the current hand-built motors, but much less expensive due to automation. Then I'll be able to buy a smaller motor that weighs less than the ME1302 but has a continuously rated output of 34+ kW. Then I'll really be able to have some fun! :mrgreen:

This battery pack will be able to deliver a maximum of 55 kW at the start, dropping to 44 kW at the cutoff voltage of 126v. However, even for the faster TAG class I shouldn't exceed 1/3 of that. I designed the bus size for an average of about 100 amps using the Handbook of Electronic Tables and Formulas for American Wire Gauge as a guide with the Maximum Amps for Chassis Wiring chart. Due to the short current path of the bus, the thinner 0.8128mm bus bars should be acceptable with the longer ones that bridge the two sides at the top getting the thicker 2mm bus bars. It could be overkill, but I'd rather be too conservative and a little heavy for the initial design than too thin and over-heat. Plus if nothing else it should keep the cells pretty even in temperature. Testing will tell the real story.

Re: EKartGo Project

Posted: Sep 15 2020 7:07pm
by hallkbrdz
BTW, here is what the future motor will be like. This is the hawk60 for comparison to what the size you see for the rather inefficient Motenergy motors.
hawk60sm.jpg (459.03 KiB) Viewed 396 times

Re: EKartGo Project

Posted: Sep 17 2020 4:33pm
by hallkbrdz
For the MOT soldering project that I'll use to solder the copper to the bus bars, I'm going to try with 4 AWG wire. But while waiting for that to arrive, I was curious how many loops of 1/0 I could fit. Two is the answer. :D No, that won't work...
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Re: EKartGo Project

Posted: Sep 18 2020 5:15pm
by hallkbrdz
Schedule of where this pack build is at - SO many things to do (and still buy)! ... sp=sharing

Re: EKartGo Project

Posted: Sep 19 2020 2:18pm
by hallkbrdz
I decided to try and find someone local to try out laser cutting the copper sheet for the bus bars. The target sheet is 24"x24" and this takes up most of it with a little space left on the sides and bottom. I elongated the holes to 8x10mm to make it easier to spot weld across the split in the nickel since the current is running North/South between the two rows of cells.

Fusion 360 file attached if anyone is interested in how that was put together (probably wrong - first time using that software). :D
20200919_busbar_sheet_layout.jpg (197.94 KiB) Viewed 313 times ... sp=sharing

Re: EKartGo Project

Posted: Sep 21 2020 6:31pm
by hallkbrdz
I updated the bus bar design to allow more space between parts. Some sites said you should have 1.5x the material thickness for distance to allow better lead-in. Not sure if that is true, but I've mailed the file and specs to a local company to see what they say. Hopefully it is a go and not too crazy expensive.

File if you are crazy curious. :-) ... sp=sharing

Also, I finished my welding pens. Design is great, but... no you cannot use steel carbide to weld nickel to nickel. It does weld the steel to the nickel very well however... So I've ordered some copper rods to try, since I'll need to use them for the 2mm bus bar welds.

I'm STILL waiting for the 4 AWG wire to show up for the MOT to try out the nickel to copper resistance soldering.

Re: EKartGo Project

Posted: Sep 23 2020 8:48pm
by hallkbrdz
MOT wire still not here :( , so I worked on the KWeld. I replaced the tungsten electrodes with copper electrodes (since tungsten and nickel bond really nice). These work great, welding .2mm nickel to .2mm nickel with about 30J as well as to battery cells and let me get into much tighter spaces than the OEM ones.

Getting copper cut using a laser is proving harder than I hoped. Maybe by next week I'll have cut bus bars.
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Re: EKartGo Project

Posted: Sep 25 2020 8:55pm
by hallkbrdz
I’m still waiting to get the bus bars laser cut, but battery support frame construction has proceeded. Pictures tomorrow hopefully (drag it all outside in the sun), but for now here is a teaser of future things.

Just for fun I quickly rendered what my clean-sheet EV kart would look like using the new (future) Tesla 4680 cells, 40s1p. I rather like it… a LOT less spot welding required. :D

BTW, the black box is what a kart has to fit in to be legal in KART.
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