BMS residual power consumption

[tarunsmehta]

Hi,

I built a 48V, 15Ah Headway pack and put in a BMS by EclipseBikes (http://eclipsebikes.com/lifepo4-576v-cell-30a60a-p-1042.html).

Now, I leave the pack for a couple of days and I notice that the voltage starts dropping pretty much constantly. Anybody know what can be the residual power consumption of these kinds of BMS?

Thanks in advance.

-
Tarun

 

[amberwolf]

Usually they're pretty small, but i fyou have the controller or other things still hooked up to the pack then they may have a much higher draw even when idle.

what does your watt meter read when each of htese is hooked up?

if you don't have a watt meter, what does a multimeter on A or mA read?

 

[dnmun]

more likely the cells are dropping down to their resting voltage. circuit current should be only a few mA, and it can be from the first 3 or 4 cells or the entire battery but it depends on which BMS.

 

[tarunsmehta]

i had a separate switch for the controller. so it's not powered on when the bike's not running.

well the voltage does seem to be settling near 51.2V (as expected from LiFePO4's 3.2 nominal).. but somehow there's a serious drop in performance. with a fully charged pack i can reach speeds of 50kmph (1100W BLDC) - but after around 5-10 kms the speed drops down to something like 25 kmph. The batteries can't give enough amperage later.. why? I can see peak current readings of ~20A or so max now.

 

[amberwolf]

what voltage does the pack drop to during the problem, vs what it is at the higher speed?

 

[tarunsmehta]

at the low speeds the voltage is around 51V, however when throttled it drops down to around 45V (btw: is the 6V sag acceptable?). At the start of the run the voltage would be around 56-57V (each cell is fully charged to 3.6V). does the 'C' rating of the cell drop down that significantly once it settles back in the 'flat-part' of the discharge?

i am charging the cells again tonight and balancing them out properly. will take them for a ride tomorrow and log data to figure out exact values.