As my app just calculate for one vesc I asked to be sure how to interpret the values. Unfortunately I don’t have an Android phone and can’t use the ackmaniak app…
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I know the difference between motor amp and battery amp. The intention behind this post is to find the right size of battery to run cool and safe and use only max batteries as needed. That’s why I asked if a 200amp battery in real life is needed… If I calculate the potential of my vescs I come to 200a…that’s why I ask. I don’t understand your statement about the battery datasheet. If I look into the official datasheets of a Sony vtc 5 or 6 or vtc 5a, they claim a constant current of 30,35a. That’s the official datasheet. I don’t know anything about any other test who proofed or has shown something else. Would be nice if you just could link it. Than i directly could have a look into it.
Lots of tests to be found there.
Ah okey I see. I would not think you need 200A continues from the battery. Hard to estimate though, will you be riding on alot of snow with big wheels?
Where did you find 30A CDR on VTC6? 20A shows almost 90deg on the battery from the datasheet. I know of no 18650 that does 30A or more continues.
Here are some tests done by mooch, he does alot of battery tests. Here is a nice conpact table for tests.
Check @Nowind videos . I think some should have video overlay… (can be found on youtube or in forum)
U should probably calculate what power u might use / need…
I think 4-5kw of power should be a good estimate… I expect at least 1-2kw when on not so good, hard roads…
On my MTB (2x 6374 150kv, 65A motor max and 50A batt max each vesc) I usually reach 130A motor max every ride but the battery max is between 60-90A. The highest value was 97A.
VTC6 are rated for 15A cont. each cell without temperature monitoring, above 15A continious they get hot. I think 12s6p is the minimum due to voltage sag and for keeping it cool.
I throw as much at it as possible within my budget to combat voltage sag and battery strain during hill climbs. Especially during winter, Lipo performance will be worse.
I have a theoretical max amp rating of 480 (Lipo setup). My VESCs are set at 60A each. Worst voltage sag I noticed during a hill climb in winter is 1V. Due to that alone, I would get even higher C rated lipos for hill climbs when my current packs are done for, despite that my setup will never get close to those numbers.
PS. I go by real life performance instead of looking at logged statistics. If I see voltage sag, there is a reason to upgrade.
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Karlo is right.
Insulation inside the enclosure is a very good point: Fibreglass is a very good insulator.
For example, my gum boots (also snow boots) that people wear in the frozen parts of the US (e.g. Denver, Colorado, etc - The same climate as Alaska, Siberia, and parts of Russia!), have a fibreglass inner boot lining, and man, they’re so warm! They’re the warmest boots I’ve ever owned. It’s my go to in Winter! At first I was skeptical since I could only think of fibreglass insulation batts used for housing… But compared to my sheepskin UGG boots (an Australian thing), they don’t even come close! I’ve got other boots that are more comfortable, but I will grab my fibreglass boots to wear, even around the house. It’s unbelievable to never feel cold in your toes in Winter.
Boats are made of fibreglass (without insulation batts), and sailors suffer freezing cold ocean temperatures at sea, and the fibreglass seems to work just fine.
Check it out: https://www.kamik.com/b2c_int_en/icebreaker-23013.html The website says they’re “Rated: -40°C”.
That temp rating will remedy what Narnash warned:
I can make you an enclosure, and make it thick for you. It should keep your battery insulated, without having to use heat pads, etc.
Check out my enclosures here: SOLIDEOGLORIA Modular Flex Enclosure [AU] -- SENDING FREE SAMPLES - New Items For Sale - Electric Skateboard Builders Forum | Learn How to Build your own E-board
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Why is it so dangerous with -15 or lower on the batteries? I drove my Tesla all winter in Norway and we had periods with -20 to -25 over weeks. No problem at all. I’ve even heard that the tesla batteries in colder climates get a much longer lifetime then in the hotter parts of the world. The battery is heated while driving but when parked I don’t have battery heating on other than for charging.
I don´t know about Tesla, but you can´t compare it with a DIY battery pack. I think the battery will likely have a way much better isolation than a small plastic or carbon battery tray, which means the battery can stand longer cold temperatures before cooling out. I could also imagine that Tesla has a safety mechanism which slightly start do discharge the cells to heat them up by there own if they become to cold. But honestly, I don´t know anything about Tesla batteries. I work with highspeed trains and can say that our unprotected battery packs, which are LiIon packs, loose capacity if the temperature falls down. But we never had any problems like blown up cell etc.
It is dangurous with arround sub -15°C battery temperature (-15°C is a figure I set for our usecase, it’s an estimate and simplification tbh) ambient isn’t the problem as long you didn’t store the board outside or expose the bare batteries to the air (hence insulation).
The problem is cold temperatures are increasing the internal resistance of the batteries, drasticly. For most batteries you can expect 50% or lower avaiable capacity at -10 to -20°C, with the high Ampareges we draw from our batteries this will result in a very fast temperature overshoot. Even though the low ambient temp. would help cooling the batteries down again, the heat is created inside the batteries and can’t travel fast enough to cool down which would cause problems.
The consequence is either a very rapid aging of the batteries, or even failing(venting) cells maybe even more furious kinds of failing. Because we use relatively small batteries such a strong increase of IR is toping out the limits of our battery cells (we don’t or can’t calculate with a max. continous current margin that can compensate a loss of 50% or more power). Big vehicles like trains, buses or high end cars even though they take a few hundred or thousand Amps usually come with way bigger batteries, they feel the loss of power (high IR = big voltage drop = slower speed) but the battery runs in spec. even with 50% les efficiency (And tbh it is to be expected that they have a some kind of thermal management for low and high temperatures to keep efficiency as high as possible)
There are tailored batteries for low ambient temperatures btw but we already need high discharge cells and want as much range as possible (at best at a low weight) these specific low temperature cells can’t deliver the performance we want.
A123 for exampe gives figures some figures about low temperature, but mind you LiFePO4 is a expensive battery technology that comes (over all) with lower capacity than Li-Ion.
Here is a diagram for a A123 18650 2.5Ah LiFePO4 cell, the more “normal” Li-Ions we use would perform even worse.
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