EM3EV max regen charge current.

[SolarFreak]

Hi all. I've picked up a second hand EM3EV 52v 14S7P battery & am in the process of setting up the regen braking with a Phaserunner controller & was wondering if anyone knows what the cut-off current is on the BMS? I looked on the EM3EV website & can only find the max charging current (8A connector limited), but as I'm not using the connector I'd like to get as much current as is safely possible without tripping the BMS, if the BMS even has a cut-off point that is. The Phaserunner automatically populates the max regen current at 12.5A which gives approx 750W regen at full braking which is great, I just wondered if this was OK & if I can go any higher?

Thanks all.

 

[amberwolf]

I would guess it doesn't have a charge current cutoff, only a discharge cutoff.

It only matters if the charge port is the same as the discharge port anyway, because that's where the regen current goes thru.

If the charge port is separate, it won't be going thru that, so any charge current limits wont' be in effect even if they exist.


The main thing to worry about with the regen is if it's high enough and frequent enough and long enough to cause overheating in the BMS FETs, since they have nowhere to put their heat into if for any reason they are not in the normal operating mode (if they shut off, they are diodes isntead of closed switches, and create a lot more heat). If it is not more than a few seconds at a time and infrequent then it's unlikely to be an issue. If yo'ure braking long and often or doing downhill slopes with constant braking then it could be.

 

[SolarFreak]

I would guess it doesn't have a charge current cutoff, only a discharge cutoff.

Hi amberwolf & thanks for the input.

According to their website: "The BMS protects the battery against over-charge, excessive charge/discharge current and also balancing." - but it doesn't state what the excessive charge current protection cut-off point is. The bike will be used for touring so the regen will be used a lot, sometimes for longer periods when descending hills/mountain passes, etc - so I want to be sure I'm within safe limits & not popping the BMS in the middle of nowhere....lol Their website has great battery info but very little details about their BMS, which is a shame.

I guess I'll have to email them & ask. Do you know if anyone from EM3EV frequents this forum?

 

[amberwolf]

there used to be several, but i've only seen posts from cell_man in recent times. https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=14820

 

[SolarFreak]

Just a follow up on this - I had a reply to my email from Joseph at EM3ev who said the max charge current for the battery is ~20A, so I'll increase my regen current slightly to 14A which is well within the limits & still gives me ~800W recharge at full braking, which is excellent.
Thanks to Joseph (cell_man?) at EM3ev for the quick response.

Edit: I've also asked them for a data/spec sheet for the BMS they use for reference.

 

[E-HP]

Just a follow up on this - I had a reply to my email from Joseph at EM3ev who said the max charge current for the battery is ~20A, so I'll increase my regen current slightly to 14A which is well within the limits & still gives me ~800W recharge at full braking, which is excellent.
Thanks to Joseph (cell_man?) at EM3ev for the quick response.

Edit: I've also asked them for a data/spec sheet for the BMS they use for reference.

You didn't mention what cells you selected when you ordered the pack, but the ~20A charging current is likely a conservative calculation based on the cell specs, since regen current won't go through the BMS.

If you chose LG MJ1 cells, for instance, they have a 3.4A max charge rating, so 7P would 23.8A max for the pack. Samsung 35E have a 2A max, so 14A for the pack. Panasonic doesn't list max, only standard charge ratings in their spec sheets.

 

[SolarFreak]

You didn't mention what cells you selected when you ordered the pack, but the ~20A charging current is likely a conservative calculation based on the cell specs

That's because I didn't order the pack:

Hi all. I've picked up a second hand EM3EV 52v 14S7P battery...

 

[E-HP]

Regen current does go through the BMS.

I don't have a EM3EV pack, but the ones I see online all have separate charge and discharge ports, which is a pretty good indication of a 3-wire BMS.

 

[SolarFreak]

Regen current does go through the BMS.

I don't have a EM3EV pack, but the ones I see online all have separate charge and discharge ports, which is a pretty good indication of a 3-wire BMS.

I took a look inside of the pack as soon as I got it home to check everything over before installing it & noticed the recharge port only uses two of the three connections which join directly to the main discharge leads, which I presume is why the packs are regen capable & is handy as I can recharge the pack via the main XT90 plug instead of messing around with the tiny charge port which I don't have an adaptor for anyway. Much easier because the pack is in a case & the charge port is inaccessible without removing the battery from the case & disconnecting everything to charge it.

 

[E-HP]

Regen current does go through the BMS.

I don't have a EM3EV pack, but the ones I see online all have separate charge and discharge ports, which is a pretty good indication of a 3-wire BMS.

I took a look inside of the pack as soon as I got it home to check everything over before installing it & noticed the recharge port only uses two of the three connections which join directly to the main discharge leads, which I presume is why the packs are regen capable & is handy as I can recharge the pack via the main XT90 plug instead of messing around with the tiny charge port which I don't have an adaptor for anyway. Much easier because the pack is in a case & the charge port is inaccessible without removing the battery from the case & disconnecting everything to charge it.

Charging through the discharge port of a 3-wire BMS won't balance your cells, so you would need to charge through the proper port on some regular cadence in order to keep the pack healthy.

 

[SolarFreak]

Charging through the discharge port of a 3-wire BMS won't balance your cells, so you would need to charge through the proper port on some regular cadence in order to keep the pack healthy.

I'm not sure you're reading my posts entirely. As I explained:

I took a look inside of the pack as soon as I got it home to check everything over before installing it & noticed the recharge port only uses two of the three connections which join directly to the main discharge leads

...meaning you are charging via the discharge leads weather you use the charging port or not - it all goes through the same discharge wires, because the charge port wires connect to them & the cells balance fine. Exactly what I wanted.

 

[neptronix]

What cells are in the pack? that's important to know, because you can find the cells' charge limits by finding their spec sheet and multiplying whatever C rate listed by 7 to get the battery's limits.. which are most concerning here, then the power that the BMS can take second.

 

[SolarFreak]

What cells are in the pack?

I don't know, I only peeped inside the end casing. I've gone with with the info EM3ev gave me - 14A of regen is plenty enough for my needs & well within the 20A max charge rate & it works very well.

Thanks for the info guys.