I'm building a battery and I may have selected an inappropriate BMS. Mine is rated for 45A continuous discharge. Can anyone tell me what the rating is for the Super Soco TC? I think I read somewhere that it was 50A continuous...do I need to get a new BMS?
Detailed tech specs on supersoco.co.uk/tc/ say Max 50A 🙁
Peak power of the motor is 3KW. Battery voltage is 60V.
Power = current x voltage, so current = power / voltage. 3000/60 = 50, so their numbers agree with themselves.
Sorry!
For some reason, I thought the motor was rated 1500W, so when I did my calculations I thought the equations would be as follows:
Watts = Amps x Volts
1500W = A x 69.7V (at full charge)
1500W/69.7V = 21.52A
1500W = A x 50V (estimate for battery a low ebb)
1500W/50V = 30A
But if it actually does run at 3kW, the equations run as follows:
3000W = A x 69.7V (at full charge)
3000W/69.7 = 43.04A
3000W = A x 50V (low battery)
3000W/50V = 60A
Interestingly, this means my estimate for how low the battery's charge will fall is too low. To calculate that, the following equation applies:
3000W = 50A x V
3000W/50A = 60V
So it appears that the lowest voltage the battery can fall to is 60V. I wonder if that's the voltage used to give the rating on the label of the battery?
Anyhow, this puts a delay on my project. I cannot complete my battery until the 50A BMS arrives. I did consider the idea that the secondary battery would never be delivering a full 50A, because it will always run in parallel with the original battery. Since the controller is limited to 50A, it will only ever draw half of that amount from each battery. But I figured that it would be better to not risk it. I'll update the forum when I finally get it finished.
Just stupid question: having a secondary battery in parallel, wouldn't sum the amps with the first battery and there is a risk to burn the FOC controller?
So original battery has 30A, if second battery has also 30A, will result in a 60A current. I don't know what is the limit of the controller, but I suspect it will just heat too much and will burn out without additional circuits to limit the current.
You're confusing Amps, which measures current, with Amp-hours, which measures capacity. A 30Ah battery can supply a current of 30A for one hour, but the max discharge in Amps will depend on the cells used.
I'm using Samsung 50E cells for my project, which can discharge 9.8A continuous, and since I'm using 6 in parallel, that means my pack could (in theory) supply 9.8A x 6 = 58.8A of current. However, as Socomods points out, the controller of the bike dictates the maximum current drawn, and on the TC that means 50A. So my pack will be able to supply that current as it is within the capabilities of the cells and configuration I've chosen. The controller won't ever draw more current than it's rated for.
The two batteries in parallel doubles capacity to 60Ah. However, the current drawn remains the same. So the bike won't go any faster (if anything it will go slower since the weight of the second battery will be added to the load on the motor), but it will last nearly twice as long a distance.
The two batteries in parallel won't make the bike go faster, but it will definitely allow you to travel at the top speed for longer.
When I was using two batteries and the paralleler on the soco, the difference caused by the extra weight was negligible, even when going uphill.
The biggest problem for the soco is the voltage drop of the battery, and the 40A (or less on newer firmware) restriction of the controller. Two batteries connected together meant the voltage dropped at half the rate, keeping the Kw available to the motor higher for longer.
The higher capacity battery you are building should have the same benefit, however two batteries in parallel would still have the advantage of being able to deliver a higher total amperage to an up-rated controller, assuming all batteries were using the standard rated 50A BMS.
Current doesn't quite work like that - the current is controlled by the motor controller, it pulls as much as it needs upto whatever limit is set and whatever max the batteries can supply combined - it already limits the current (still vague on definitive figure, but as the motor is 3kW, it can't be more than 50A, perhaps 40A on limited bikes), changing the battery wont change that - but you are right, if someone changed the controller limit without considering all the other parts running high current levels, things could go wrong
Where did you buy the 18650 batteries and what price did you pay?
I just did a small calculations by myself (I haven't checked physically, even if the battery is inside the house now - winter outside, too lazy to find the screwdriver and I am also a bit afraid to not break something).
So... the battery is 17s12p, which mean a total of 204 batteries.
A good LG/Samsung 18650 battery is probably not cheaper than $5, so in total only batteries price will be ~1000$.
Add effort, time, BMS... of course a generic BMS will not communicate the percentage of the battery, so you'll have to "feel" 🙂
Wouldn't be cheaper/faster to buy directly a new one? 😀 It's €1000, found it here https://2roueselect.fr/en/59-batterie
Of course if you're hobbyist and you do it for fun, ignore me 😀
Good questions. At the time, the cheapest I could get a new battery was €1300, plus shipping to Northern Ireland. So my cost basis when making the decision was a little different.
Next thing is, I didn't buy 18650 cells. I got 21700 cells instead. As an investor in Tesla, I happened to know these batteries had a greater power density than 18650 cells. So I can make a battery that is only 17s6p, adding significantly less weight to the bike. This will increase range for the same capacity of battery. The other advantage is that with these cells, I have room in the storage bin for another two batteries, which would increase the capacity to 90Ah.
Outdoordreams now have the original BMS on sale. So with my skills, I could now replace the original battery also. Packed in the correct configuration, I could fit four batteries of 17s6p configuration in the space that's available, making a total capacity of 120Ah.
I use the bike as a business for delivering food, so I can write the cost of upgrades off against my tax obligation. The more range I have, the more money I can make in a day.
Later I read again your post and realized you're using 21700 and not 18650 🙂
Well good luck and continue to keep us updated with your project.
Also in my country, if I buy the battery from the dealer, I get it with the same amount of €1300 (probable the shipping is negligible), so if you manage to build a cheaper and better range battery, I would be also interested.
...
Outdoordreams now have the original BMS on sale. So with my skills, I could now replace the original battery also. Packed in the correct configuration, I could fit four batteries of 17s6p configuration in the space that's available, making a total capacity of 120Ah.
...
Isn't that a REALLY heavy battery? 17 stone 6 pound = 244 pounds. A pair of standard Soco batteries is only about 50 pounds. Seems like you're going to lose some speed over that 96-pound addition. Unless I have my numbers wrong. :/
If this is a joke, it's both funny and well executed. Obviously you know that 17s6p refers to the 17 cells in series and 6 in parallel, and not the weight of the battery. Clearly you're just having a good laugh at my expense. Right?!
@csocobelfast
I think you can manage with 40A bms if you parallel. Because when you do the total A drawn by motor and controller combo is shared by the batteries attached.
I think the original motor power were 2440w for TS and almost 3000W (2880) for the TC so calculating max Amp draw is 69,7v * A = 2440 and 2880w respective ->
35A for TS and 40,5A for TC. However I think the TS battery can give 40A as I sold my TS battery to someone saying a retailer said to him that the batteries are interchangeable.
btw, it's already confirmed in a previous post: some dealers sell the 69.7V charger, others 71.4V.
By example @socobelfast charger is 69.7V and he charges his batteries to 4.1V, which is better for battery life and allows dealers to guarantee the battery for probable 2 years.
My charger is 71.4V and it will bring the batteries to their maximum (4.2V), maybe my dealer don't care too much and it's more work for me to be sure I remove from charger before full.
Anyway we should consider a 71.4 * 30 Amps because this is the real maximum power the battery has.
PS: it's something strange... when I charged (only once until now) to 100%, actually until the charger light turned green.
I drove to work 6kms and I barely consumed 2% of battery 🙂
Then I returned home and the same 6kms consumed 9% (from 98% to 89%).
I have a difference of altitude (down hill going to work, up hill back home), so I believed this explains the difference.
But now I think actually the BMS lies and shows 100% between 4.2 -> 4.1, then starts decreasing the percent.
I will have to retest and prove this in the spring and on flat.
Yeah maybe you are right that it will hide the last percentage. The % meter shouldn't be taken to be 100% exakt as the level of energy for ever voltage level isn't exactly linear.
Maximum charge for the Soco battery that is tested is 12a for non-original charger and 15a for original charger. My max charge has been 8a on my Soco TS battery of 26ah. I don't know what max charge a super soco battery can take but if you go higher the battery may turn off because of high temperature protection kicking in after a while charging.
https://supersocoforum.com/forum/main/my-15a-fast-chargers-have-arrived-and-they-work/#post-1099
