k-harvey
100 W
With a device that has a LiFePo4 battery (12v 50a BMS ) & further distance( AH) is required can an SLA acid battery be added(parallel) of same v without chance of LiFePo4 cell damage or BMS.
SLA battery added to LiFePo4
- Thread starter k-harvey
- Start date
dogman dan
1 PW
I wouldn't hesitate to do it. But more likely is damage to the sla, since the lifepo4 can tolerate discharge below 12v better.
k-harvey
100 W
Thank you again, I have many SLA that would end their life at this(they are near that way now)but have to look after LiFePO4 battery . Although is there a simple Low volt cut out that added could save the SLA?
scoot
1 kW
- Joined
- Apr 30, 2009
- Messages
- 392
I tried something similar once. Used a Headway Life pack w/25 amp BMS in parallel with some SLA batteries. Used a Cycle Analyst meter to monitor the current in and out of the SLAs. My scooter is usually pulling 30 to 60 amps with some hard riding. Found the current draw from the SLAs was significantly less.. maybe a third. When i stopped in the middle of a ride, I could see the current direction reverse resulting in a charge current from the Life pack reading 2 to 5 amps pumping back into the SLAs depending on how deeply discharged.
Ended up dropping this approach... but I thought maybe I needed a higher current BMS... like maybe 50 amps to keep up with the higher SLA discharge... just dunno. Anyway, during the short period I fiddled around this way, it didn't seem to adversely affect the BMS, or any of the batteries. Might not be same experience though with other circuitry. I charged them independently and did not leave them connected that way when I was storing the scooter without a charger. I have read a lot of posts about using high current diodes and other devices to prevent current reversal.
Ended up dropping this approach... but I thought maybe I needed a higher current BMS... like maybe 50 amps to keep up with the higher SLA discharge... just dunno. Anyway, during the short period I fiddled around this way, it didn't seem to adversely affect the BMS, or any of the batteries. Might not be same experience though with other circuitry. I charged them independently and did not leave them connected that way when I was storing the scooter without a charger. I have read a lot of posts about using high current diodes and other devices to prevent current reversal.
dnmun
1 PW
yes, you always have to use a diode when combining packs of different voltages or chemistry.
if the two pack combined in parallel are identical in voltage, chemistry, and capacity then it makes sense to use them without a diode between them. all other cases require a diode.
put the cathode of the diode on the higher voltage pack such as the lifepo4 in this case. put the anode on the SLA.
if the two pack combined in parallel are identical in voltage, chemistry, and capacity then it makes sense to use them without a diode between them. all other cases require a diode.
put the cathode of the diode on the higher voltage pack such as the lifepo4 in this case. put the anode on the SLA.
dogman dan
1 PW
Diode on the lifepo4 pack would prevent any unwanted flow of power back into the bms, through the discharge leads of the bms, protecting it.
Diode both, and then you cannot have flow back into the lead. Then you could monitor the lead, and unplug it at the DOD you choose.
It could be perhaps just easier, to run the lead awhile, then switch to the lifepo4 to finish the ride.
Diode both, and then you cannot have flow back into the lead. Then you could monitor the lead, and unplug it at the DOD you choose.
It could be perhaps just easier, to run the lead awhile, then switch to the lifepo4 to finish the ride.
DrkAngel
1 GW
You do not want "flow back into the lead"!
Lead requires ~150% input (33% loss) to acquire Ah. (wasted drain from lifepo4 )
Additionally, output from SLA at a 1C rate only produces about 60% efficiency.
Lead requires ~150% input (33% loss) to acquire Ah. (wasted drain from lifepo4 )
Additionally, output from SLA at a 1C rate only produces about 60% efficiency.
Dauntless
100 TW
DrkAngel said:
What is the most efficient rate for SLA?
DrkAngel
1 GW
Most SLA batteries are "rated"-tested at a .05C discharge rate ... 20 hrs!Dauntless said:
There is another class of SLA that are rated at .2C discharge rate ... 5 hrs.
Optimal charge rate is typically quoted as .125C ... 8 hrs.
Sad ... even for 20th Century technology, it sounds fairly pitiful!
But ... cheap, and a reasonable "starter battery".
k-harvey
100 W
Hi --the device I'm using the LiFePo4 12v 20ah is for a what we call a fishing torpedo which goes up to 2 KM out to sea so adding another battery out there wouldnt work . We have always used SLA batteries adding 12 ah batteries to 7 ah etc heaviest weight is when we have 2 -12 ah plus one 7ah no diode etc The one 12ah plus 1 7ah use up their power in about 20 minutes (with timer)so the c rating(which i cannot find written on any) must be quite high.
Ive made this Torpedo especialy for LiFePo4 battery so lighter for the back & goes much faster*(since Ive made battery packs for e bikes) & because one time using it the timer did not cut out I've lost a few AHs & last time out did not go as far , I'm proposing to add one of the SLA 7ah with it, Will look for Diode today also need 50A fuse which blows when stones etc stick to propellor --hell perhaps i should stick to SLA even for bikes its simpler.---But heavy.
A commercial one sold here sells LiFePo4 pack that is added to SLA so will try to find out from this guy what extra it has.
Ive made this Torpedo especialy for LiFePo4 battery so lighter for the back & goes much faster*(since Ive made battery packs for e bikes) & because one time using it the timer did not cut out I've lost a few AHs & last time out did not go as far , I'm proposing to add one of the SLA 7ah with it, Will look for Diode today also need 50A fuse which blows when stones etc stick to propellor --hell perhaps i should stick to SLA even for bikes its simpler.---But heavy.
A commercial one sold here sells LiFePo4 pack that is added to SLA so will try to find out from this guy what extra it has.
k-harvey
100 W
On the 2 wires to SLA battery have 3 Diodes together as cheap bt told it won't work as they stop flow at different time but need 3 to be a big enough wire for the current (thats if it don't burnout) I'll see how this goes this week .
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