Johnbear
10 kW
GGoodrum said:
This is where the sla charger with lifepo4 was mentioned. I guess it depends on the CMS.
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Duct Tape E-Bay Lifepo4s???
- Thread starter Johnbear
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This is where the sla charger with lifepo4 was mentioned. I guess it depends on the CMS.
GGoodrum
1 MW
Actually, using SLA chargers are fine, if they have a standard CC/CV charging profile, and if the crossover point is at least around 44-45V, for 12-cell LiFePO4 packs, and 58-59V for 16-cell packs. LiFePO4 cells need a CC/CV crossover point of at least 3.65V per cell, but are pretty tolerent going as high as 3.8V per cell. Most SLA chargers pick a crossover point that represents the number of cells x 2.40-2.45V. For an 18-cell 36V SLA pack, this works out to about 43.5-44.0V. For 24-cell 48V SLA setups, the voltage works out to 58.0-59.0V-58.0V. The minimum a 12-cell LiFePO4 pack needs is 43.8V, and 58.4V for a 16-cell pack.
SLA chargers also typically have a trickle charge mode, for keeping the battery "topped off", and this mode is apparently being used by the balancer circuits on the BMS to keep feedng current while the high cells are being bled off, to match the lower ones. I'm not a big fan of these RC-styled balancer circuits because they don't work very well sown the road, when the cells start to drift apart slightly in capacity and internal resistance. Some cells just won't get abaove a certain point, so what happens is all the rest just get pulled down to the level of the weakest one. To truely get all the cells to their individual 100% charge level, you either need to use individual CC/CV chargers, like ypedal is doing, or you need to have a zener-like voltage regulator on each cell that will limit the voltage to 3.65V, so that the cell can gradually reduce the current it accepts as it gets full, but whatever the cell doesn't use, current-wise, gets bypassed. That way the next cell in series can get all of the current, if it needs it. This shunt-type regulator is what larger EV applications use in there BMS units. the problem with trying to do this on a small ebike pack is that you have to dissipate the heat generated by the bypass process, which can be quite a lot. The advantage of the shunt/bypass approach is that the cells can be charged with higher currents.
What Bob and I decided to do was to move these shunt regulators to an external unit, which is what we are calling the "CMS". That way we can manage the heat a lot easier, and get the best of all worlds. He's designed it so that we can run up to 8A through the CMS. This dictated that the wires and the multipin chargie plug be able to handle up to 8A as well. that's why I picked the Molex-type connector that I'm now using on the LiFeBatt packs. You need 16-18 gauge wire in order to carry 8A to each cell. Anyway, more on this later, in the LiFeBatt thread.
-- Gary
SLA chargers also typically have a trickle charge mode, for keeping the battery "topped off", and this mode is apparently being used by the balancer circuits on the BMS to keep feedng current while the high cells are being bled off, to match the lower ones. I'm not a big fan of these RC-styled balancer circuits because they don't work very well sown the road, when the cells start to drift apart slightly in capacity and internal resistance. Some cells just won't get abaove a certain point, so what happens is all the rest just get pulled down to the level of the weakest one. To truely get all the cells to their individual 100% charge level, you either need to use individual CC/CV chargers, like ypedal is doing, or you need to have a zener-like voltage regulator on each cell that will limit the voltage to 3.65V, so that the cell can gradually reduce the current it accepts as it gets full, but whatever the cell doesn't use, current-wise, gets bypassed. That way the next cell in series can get all of the current, if it needs it. This shunt-type regulator is what larger EV applications use in there BMS units. the problem with trying to do this on a small ebike pack is that you have to dissipate the heat generated by the bypass process, which can be quite a lot. The advantage of the shunt/bypass approach is that the cells can be charged with higher currents.
What Bob and I decided to do was to move these shunt regulators to an external unit, which is what we are calling the "CMS". That way we can manage the heat a lot easier, and get the best of all worlds. He's designed it so that we can run up to 8A through the CMS. This dictated that the wires and the multipin chargie plug be able to handle up to 8A as well. that's why I picked the Molex-type connector that I'm now using on the LiFeBatt packs. You need 16-18 gauge wire in order to carry 8A to each cell. Anyway, more on this later, in the LiFeBatt thread.
-- Gary
albie
100 W
I'm still waiting for my battery pack
PJD
100 W
I Have heard this, but I've also heard (from Valence and others) that the LiFePO4 charging protocol is exactly the same as an SLA pack. So, if the voltages and maximum current are the same, it seems a SLA charger will work fine.
As far as YPedals setup. I know a lot of e-bike hobbyists pursue pursue fancy, complicated setups like that shown, but, if I showed that photo anyone looking for an e-bike as practical transportation, I'd scare them away.
Johnbear
10 kW
Thanks Gary for clearing that up.
Albie, who have you ordered your batteries from? How long ago? Did they give you a working tracking number?
Albie, who have you ordered your batteries from? How long ago? Did they give you a working tracking number?
Johnbear
10 kW
Curiosity got the best of me so I had to take the duct tape of. Pictures shortly-
Johnbear
10 kW
The duct tape is very neatly applied I must say!
View attachment 1
This stuff makes me kind of nervous so I was very slow and careful!
Johnbear
10 kW
View attachment 1
Well it all looks ok, It will be shrink wrapped soon when I go to ebikes.ca on tuesday for some white shrink wrap.
PJD said:
Sorry, my bad, I should have said It the way Gary Explains in a previous post, which I asked him to do. SLA Charging can be done - but has a little different set of challenges that many SLA Chargers don necessarily offer, and probably need to be tweaked in order to do it right.
Don Harmon
Foil pouch.. in duct-tape..... 
You do realize this needs to be set in a solid box to protect it .. not just a canvas bag either.
Anything that pokes thru the very thin foil layer, shorts it.
That looks awful similar to cheer ocean handy-work.
Yes, these are what's called "prismatic cells" but they are primitive in that they are just the foil pouches and not encased in their own plastic modules at least like what PHET offers or even Thundersky. So what you have is pretty wonky as far as being a "hard pack solution". It's really a box of cell pouches, and YPedal is right - you really need to protect them much better than duct tape is ever going to do!
It's the old saw - you get what you pay for, but you knew that already :lol:
Best,
Don Harmon
It's the old saw - you get what you pay for, but you knew that already :lol:
Best,
Don Harmon
albie
100 W
i'm getting mine off anna... i have put through a paypal dispute / an ebay dispute. Last i heard she was supposedly checking what was happening at the post office ASAP... i've sent an email 2 days later asking what happend and no response!
really annoying as its now over a month and i still have no battery!!!
really annoying as its now over a month and i still have no battery!!!
Johnbear
10 kW
I cut out some hard plastic for the base, covered the battery I have been using in tool box liner and then put some light weigh 1 inch light foam plastic over it. - You could take the battery off my bike directly and mail it - it is very well protected.
Johnbear
10 kW
I had to check the charger with my watts up out of curiosity. It does not float charge like a sla charger. I shuts down when the batteries are full after the constant voltage cycle.
View attachment 1
Inside of charger for those who are curious.
View attachment 1Inside of charger for those who are curious.
kbarrett
10 kW
And now for something completely different ....
I got a good run out of ping's duct tape pack, 16 miles, only 2 volts down from the starting resting voltage of 40V on a sub freezing day ... not bad.
I thought I could commute with this alone ... but then I took the battery out to charge it ... and noticed a funny smell.
Melt down ... the FETs all burned. it looks like the battery current on the negative lead does route through the BMS ... one short 36 Amp hill-climb and they burned.
The battery still works just fine ... but recharging it is going to be a problem.
I was not using this battery in series ... I was using it alone, attached to a new 36-72v 35A controller, with a Crystalite 405 on a 20"wheel.
I got a good run out of ping's duct tape pack, 16 miles, only 2 volts down from the starting resting voltage of 40V on a sub freezing day ... not bad.
I thought I could commute with this alone ... but then I took the battery out to charge it ... and noticed a funny smell.
Melt down ... the FETs all burned. it looks like the battery current on the negative lead does route through the BMS ... one short 36 Amp hill-climb and they burned.
The battery still works just fine ... but recharging it is going to be a problem.
I was not using this battery in series ... I was using it alone, attached to a new 36-72v 35A controller, with a Crystalite 405 on a 20"wheel.
albie
100 W
wow... looks like you will need a new bms!
kbarrett
10 kW
albie said:
Looks like the vendor needs to consider sending me a better replacement, if he wants to sell more of these.
kbarrett
10 kW
I can hear you snickering at your keyboard all the way here to Camas, Don. :wink:
Oh well ... we'll see if Ping has a better BMS ... he did state that the one on this pack was superseded ( although he was blaming 72V series use for the burnouts ).
My house now smells like burned FETs.
Oh well ... we'll see if Ping has a better BMS ... he did state that the one on this pack was superseded ( although he was blaming 72V series use for the burnouts ).
My house now smells like burned FETs.
kbarrett
10 kW
I'll be satisfied with a better replacement BMS ... the pack is still working as a battery. I could probably ride another 20 miles on it as is.
Johnbear
10 kW
I wonder if putting a heat sink on the fets would help avoid this? Maybe I should get out some thermal paste and a heat sink?
Johnbear
10 kW
My yesa pack had a broken resistor on the BMS from shipping and Sam sent be a new resistor and BMS for that pack, so I hope ping is quick to fix you up.
Arbiker501
10 W
- Joined
- Dec 22, 2007
- Messages
- 88
Don
Heck you could just buy a pack and do a full head to head comparison .. Then report to us what you find..
Heck you could just buy a pack and do a full head to head comparison .. Then report to us what you find..
