crf450r 40kw with watercooled battery pack


riverin

Well-known member
Location
saguenay
I have experience with DI coolant fluids (Dialectric) with fully emersed packs and you'll need to design the cell layout with that in mind. You need to use greater than normal cell spacing to get enough flow to make any difference. This will make the pack larger than most you see where the cells are literally touching (a terrible practice to begin with). In addition, you'll need to make sure to expose the maximum cell surface area for same. Some means to compensate for fluid temperature increase as it flows through the cells might be in order depending on the total flow distance and delta T. Keep this as short as possible. Finally, the couple of fluids I've dealt with were both very expensive ($100 a gallon). This means keeping track of every oz you can during pack/bike maintenance. Some (like mine) need special expensive solvents to fully remove, making electrical and mechanical repairs difficult. The most troublesome characteristic of these fluids is the extreme level of capillary action and material compatibility. If there's even the slightest of porosity inside the pack, that fluid will find it and start to leak (and it's a pain to clean up as mentioned). It also dissolves or at least softens many kinds of rubber and sealants. In addition to the obvious, this can cause issues with some passive and active electronics if you intend to pack any internally. Short term I had no issues with flooding an Alta pack. It weighed a ton more due to the total case volume (another point to keep in mind), but I didn't experience any cell of electronic failures. I gave up on the concept become it was a pain to keep sealed and it didn't do much cooling. What cooling it did do produced large differences in cell temps top to bottom, side to side. Longterm, the modules I had used in that experiment all ultimately died while sitting on the shelf. Definitely do your homework or (as I found out) the benefits won't outweigh the problems.
Hey mark may I ask you what type of thermal interface you used to connect the cells to the cold plate? Or at least what the original alta pack used?
 

Mark911

Well-known member
Location
Corona Ca
Hey mark may I ask you what type of thermal interface you used to connect the cells to the cold plate? Or at least what the original alta pack used?
The Alta pack uses a passive system with the thermal plate (and some imbedded heat pipes) sandwiched between two modules. The thermal "plate" is very thin (about .050) and given the same thickness to the pack housing (radiating surface) simply can't move enough heat when the going gets tough. Everyone's probably seen pictures and understand this. The other limiting factor is that only the negative end is thermally connected to the plate using electrically isolating thermal conductive film adhesive. Now, studies have shown that the negative end IS the best place to pull heat out due the "jellyroll" design making heat much easier to move in the axis of the cylinder. That why Alta kinda invented the one-sided cell electrical connection, but it's also reason for some of the reliability issues. Heat moving radially is resisted by all the layers of insulation between electrodes. Tesla uses radial cooling (core to sides), but they cool the water first (using the onboard AC) making for a much higher delta T which and along with the increased surface area, more that makes up for the poor thermal path. Here's the rub, even the negative end ultimately (thermal wise) chokes down to the width and thickness of the final "pigtail" on the negative electrode which is only spot welded to the end of the cell. That's one reason cells of virtually identical specs can vary so much in max continuous discharge rates. For "negative end" cooling (like the Varg), cells using 100% of the negative electrode in thermal contact with the cylinder end offer the best possible thermal path. Not sure if the Varg uses these or not, they're very expensive and hard to get. Then you need to make sure you don't waste all this thermal efficiency by using a TIM (thermal interface material) from cell end to your thermal plate with the highest conduction rates while still being electrically isolating, a tough ask as the materials tend to be opposite in nature. You could isolate P groups and bond conductively only and/or mechanically connect only to "islands" of thermal plates and therefore not worry about shorting, but manufacturing wise it would make the pack very expensive and it's not practical. Any external electrical path (a screwdriver) between isolated islands and "poof". Finally, you need to make sure your plate/housing/whatever, can dissipate the required heat ultimately using ambient temperature (air temp) as the thermal conductor. Air is a crummy conductor, particularly when you consider that there's not much delta T between air, at say 80F, and the max cell temperature (assuming no active system like Tesla where pre-cooling can be done). I personally question Vargs cooling plates, they don't have much fin area and that's what counts. I have no idea what TIM they use.

Now, my experimental Alta pack was modified by enlarging the electrical wire mouse holes in the thermal plates. This allowed fluid to flow between modules. This was tricky as too much could compromise durability of the cases. Getting the fluid flow to "circulate" properly took some work. Large AN fittings were attached to a custom made lower cover and upper cover. The lower cover was needed to keep volume as low as possible and direct fluid intimately over the bottom module. The system directed the fluid in a "bottom to top" direction. The stock module safety covers were removed in this experiment. Fluid would enter from the lower cover front and naturally flow to the rear where low pressure and the enlarged mouseholes were. Fluid would then continue to the second module (counting bot to top). In the center (between case halves and mod 2 and 3) I added a thin plate (non-conductive) slightly open at the front which helped keep the flow intimate to the cell tops of the 2nd mod and redirected flow over module three. It would then repeat the process going up through the upper case mouseholes and wash over the forth module as it exited the front of the top cover. The BMS cover assured intimate contact with the top module cells. Obviously, a pump and typical fluid to air radiators were used.

Here's the qualifier. The Alta cell "honeycomb" didn't allow any flow between cells, it's just that way. So, the idea was to remove heat from the positive ends of the cells just like the negative ends. Typically, this is prevented due to the interconnects, but with fluids these constraints don't occur. I haven't seen any studies about the efficiency of positive end thermal conduction, so I was kinda flying by the seat of my pants. Like I said before, I dropped the concept due to the hassle of buying and using DI fluids and lackluster results. But I'm not saying that with much more research it couldn't be a viable solution. At least until better cells are made commercially available. My bet is with the cells, and that's many years away, Lol.

The pack I built for my KTM supermini 85 was designed to cool both cell ends using water. The cells themselves never see the water, so no short worries. The double sided cooling is something I invented but probably wouldn't do it again. The tolerances of the cold plates and virtually every aspect of that build had to be way too tight, like +/-.005. While not a big deal for a CNC machine, at the final assembly level things wern't so simple.
 

Brillie35

Make Alta Great Again
Location
Netherlands
Sorry to bring this up, but didn't you build a electric conversion before?
That catched on fire?
I was wondering if you ever find out what happened, and what you are going to do to prevent it this time.

ERM.png
 

Mark911

Well-known member
Location
Corona Ca
Anyone who keeps a DYI electric bike in their attached garage is flirting with disaster (detached is better but still big dollars if it burns down). I once had 5 conversions, 2 Altas, an electric kart and tons of cells and half-built packs in my attached garage and literally couldn't sleep at night. One of the big reasons I sold almost everything and what battery stuff I have left is kept in a rented sea container 150 feet from my house. The numbers are small, but statistically, the more popular DYI gets the more fires you'll be seeing even if the % failures don't change. Particular when using non name brand cells from China. That could be bad for some businesses and the sport in general.

Obviously, some DYI packs are built safer than others. I've posted NASA's findings on preventing thermal runaway several times on this and other battery DYI sites and never got one question and few views. So, I just gave up promoting battery build safety as people are going to what they want with the budget they have, and I actually applaud them for being so industrious. They just need to know the risks.
 

riverin

Well-known member
Location
saguenay
Sorry to bring this up, but didn't you build a electric conversion before?
That catched on fire?
I was wondering if you ever find out what happened, and what you are going to do to prevent it this time.

View attachment 9707
The reason of this fire was that I was using Chinese bms with bypassed discharge. Basically no protection to the cells if the voltage get too low on one cell group. This time I am using the ennoid bms in charge and discharge.
 

riverin

Well-known member
Location
saguenay
Anyone who keeps a DYI electric bike in their attached garage is flirting with disaster (detached is better but still big dollars if it burns down). I once had 5 conversions, 2 Altas, an electric kart and tons of cells and half-built packs in my attached garage and literally couldn't sleep at night. One of the big reasons I sold almost everything and what battery stuff I have left is kept in a rented sea container 150 feet from my house. The numbers are small, but statistically, the more popular DYI gets the more fires you'll be seeing even if the % failures don't change. Particular when using non name brand cells from China. That could be bad for some businesses and the sport in general.

Obviously, some DYI packs are built safer than others. I've posted NASA's findings on preventing thermal runaway several times on this and other battery DYI sites and never got one question and few views. So, I just gave up promoting battery build safety as people are going to what they want with the budget they have, and I actually applaud them for being so industrious. They just need to know the risks.
That was one of the reason I wanted to use immersion cooling. I saw somewhere that if a thermal runaway was to happen it would stop to the single cell because the coolant would extinguish it. Actually I would like if tou would tell me about that stuff.
 

Warren

Active member
Location
Enfield
Very clean professional build.

I find it puzzling that you are able to do this work in your garage but somehow Honda cannot. Bizarre, I think the OEM are just sand bagging to milk their current product lines as much as possible. I think they will get Tesla’d and soon be screwed if they don’t start trying. Actually forget them we should support Stark, Sur Ron and Admit Jet and boycott their crappy 20th century junk. RIP Honda motorcles.
As Ktm said went they were looking at the Alta MXR RedShift batteries 🔋 are too expensive to put in a bike and make the profit they make from an ice bikes. And remember, they said that there, FACTORY, Tessa rider, drained the batteries in less than 15 minutes plus overheated it also just not feasible and profitable yet. Will have to wait for the next generation battery to come along. Will see when the stark Vark finally hits the market how well they did in this issue. Could be why the wait has been so long even with all their money influx. Fingers crossed as we love our E motorcycles..
 
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