FocBox Tenka Question(s)

I currently have a focbox tenka Im attempting to put into my evolve gtr. I have found no (helpful) videos online for such a project. I’m wondering if I will be able to put a tenka into my board with the stock bms or if it will cause issues. The motors I’m putting in aswell are Flipsky 190kv 6354 motors to give the board a bit more kick. I’m attempting to calculate the continuous discharge of the evolve battery to check compatibility but I’m having some trouble. I have heard that the evolve bms is quite a pain in the behind and I don’t want to blow my motors/esc/battery by just throwing it all together without any prechecks. Im also looking for an effective vesc tool to set up my tenka, any help is appreciated!! Thanks!

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I believe the bms communicates with the stock esc. If you get full voltage at the battery output connector with the esc disconnected it should work. Do you?

Oddly enough, I actually get 41.2V at the battery output, but the battery is theoretically rated at 36V. Am I missing something?

No that’s actually correct. 42v is max charge on a 36v nominal battery (or 10s battery). As for the whole battety and bms thing, you have to open the pack and see what batteries they’re using. If its an evole, its definitely a samsung 35E cell. But double check by opening it a bit and see the brand on the battery.

If it is, just know what battery is it built as.

For example:

Is it a 10s4p a 10s7p, etc. You can find the rest afterwards once you know the battery brand and built.

I have already checked the battery case and you’re definitely right, they’re Samsung 35E cells arranged as a 10s4p. Could you maybe explain a bit more if possible on why a 36v nominal battery charges to 42v? Is this the case for all batteries as well?

I can share that. 36V is basically a 10s battery pack because the nominal of a single cell is actually 3.6v or 3.7v depending. It can be as low as 3.3v with life04 cells. Not all batteries are the same (the example being life04). But majority of 18650/20700/21700 cells all goes by the 3.6v nominal of a cell. They all charge to 4.2v at max. This is also the same for lipos as well.

But to save all the time, batteries such as 35E are rated as 3.6v nominal. And if you are making them in series, you would multiply them by the nominal so you can get close to what you need from a battery. For example:

An 18v battery is basically a 5s battery. A 36v is a 10s battery, a 12s is 43.2v nominal. Basically, your battery series build determines your voltage. Now that you know this, the bms of that battery should be rated around 40-45A as discharged voltage since 35E cells are rated 8A per battery in p grouping. Since your battery has 4p, it would be 8x4, which is 32A.

For this reason, the bms sucks on the evolve because if you try to take more than 40A, you’ll basically fall flat on your face due to the battery cut off. This is why people would bypass the evolve bms and make it charge only. In other words, remove the negative (black) wire from the bms and put it on the battery negative side (usually found since the bms needs the b- side to make it work as a charger), and you’re set.

Thank you! Thats super helpful! So in regards to the evolve bms, you’re saying that by removing the negative battery terminal from the bms and connecting it straight to my esc in this case, I can utilize more amperage from the battery? It is safe to operate the battery without the bms connected?

Yes, however, since they’re 35E cells, you’re not really gonna be using much. Especially if its a dual esc. You’re gonna have to divide your amps by 2 for each esc. So you only have 15A to work with (safety amps). Removing the evolve bms discharge lead just saves trouble in case your set up just tries to steal more amp for just a split second.

Look more into BMS bypassed batteries. But, saving pointless readings, The only thing you need to note is that you do not use your brakes on a full charge. Discharge your battery down before braking. 41v or less will be safer for you to brake. After that, everything else is done via the esc like battery cut off voltage. Bms just turns off your brakes if you try to brake at full charge and keeps your battery safe from overcurrent (braking at full charge) and undercurrent (esc trying to steal more than necessary. This only happens if you didn’t program the cut off).

Most of us use our bms as a charger only. Works like a charm.

The last thing i need to say is this:

Do not operate the tenka above its rated discharge motor current. If it says 65 A current max, put 60. That esc will cut out if you go above the rated line.

is it worth it to bypass it if I’m not going to get much more out of it? it seems like if its a safety in place and I don’t gain anything from removing it, it much not be worth it to mess with it at all until I get a new battery. If I leave it in it will still function per usual, correct?

Does this also mean I dont connect the bms to my esc if I choose to circumvent it?

Also, the evolve bms has 6 pins and the FocBox only has a space for 5 pins to connect the bms, any ideas?

Yes because its an evolve bms… I don’t think I need to go further there…

This is exactly why you bypass it. Its a Bluetooth module esc and will work only with a second switch that is on the bms, which connects to their specific esc. Basically, that bms will be 100% incompatible with your esc.

No. If anything, just get yourself a different BMS and save the trouble of using that one. Evolve makes their esc and bms specific to their build and the best option is to just replace the bms. Trust me.

I did exactly that.

Alright thank you! Any recommendations for a bms?

I brought a cheap daly 10s 36v bms. Just do a bms bypass and you’ll be good. Don’t worry about discharge amps.

Sorry you may have explained this, but how would I do a bms bypass with the evolve bms using 6 pins and the tenka using only 5? Or are you referring to doing a bms bypass on the new bms I’m going to order? Thank you again for all your help! You’ve made this project worlds easier on me!

You have to look at the bms and find b-. It will say it on on the bms (and already soldered on the battery negative side). Then find P-. P- is the black wire. Remove the black wire from the p- and solder the black wire on to the battery where you find the b- wire soldered to. That is called bypassing bms. Basically, you’re no longer using the bms, but the battery itself.

Think of it as setting it up so you can add the bms later on. The bms is basically your charger for your battery if the evolve bms does not charge your battery.

I definitely believe it will not. But you can test this by doing the bypass thing and then connect your charger to see.

key Note: DO NOT REMOVE THE B- WIRE FROM THE BATTERY! That is what powers the bms (unsure on the evolve bms since its a Bluetooth switch bms which needs to be switched on to work). But you need that to remain soldered on to test charging. Only remove it if it does not charge the battery (the charger light doesn’t show its charging the battery).

You can leave it on until you get the other bms. Then all you have to do is solder where the old b- was with the new b- on the new bms. Then proceed to solder the leads accordingly.

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So effectively I’d be bypassing the evolve bms in hopes that it’ll still charge, however unlikely that is. But in doing so, I’m preparing the battery/bms for a new bms that I have on order to replace the evolve bms? Is the idea that regardless of bms, I should use a bypass because of the type of cells evolve uses/ safety features they have in place on the battery? I’m just trying to wrap my head around the “why” of how this works so I can replicate it in future. Thanks!

Simplisticly, yes. You are removing a horrible bms for a better one. Evolve bms gives some people issue and this is usually why people would bypass it. That bms needs more things for it to function, which sucks.

I don’t follow here. The reason of using a bypassed bms is because bms can fail at any giving point, causing you to no longer use the battery via bms discharge. You are also removing the limits the bms can give. Some bms could be rated higher discharges, but can still be damaged because of the esk8 and how low to the ground it is.

Basically, vibrations can cause issues on some bms and for this reason it’s best to bypass. This also helps because if something happens to the bms, you can easily replace it with the same one. My bms broke due to heavy vibrations.

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I guess my final question is what should I rate my motors at for amps when programming the focbox? Should I only give it 15a each side?

Depends on the motors. But the tenka can produce 60 amp per motor max for safety.