Tenergy 48v LiFePO4 charger question

[Old_Scoot]

I have a question about this charger:
http://www.all-battery.com/TenergyBatteryCharger01311.aspx

The specs listed say it is for a 48v 15S LiFePO4 pack. Isn't 16s the standard for "48v" LiFePO4? I think the 15S must be a typo since it lists a maximum output voltage of 58.2. That would be 3.88 per cell. At 16s it would be 3.64 which sounds more like a LiFePO4 voltage. Right?

 

[evblazer]

15s looks like it is all over the place. In the manual. On the label of the charger itself..
If you look in the manual at the charging section it mentioned 3.65 per a cell max it also mentions in the manual the 58 volts is the open circuit voltage and a few references to 15s. Charger label has 54.7 which would be 15S. Nothing on the tenergy website they point to though :?

0-T1:
Precharge stage. When the voltage of the cell is lower than 2.5V±0.1V, the charger will use pre-charge
current to charge the battery.
T1-T2:
Current ramp up stage. When the voltage reach to 2.5V±0.1V, charge current will ramp up from wake up
current, and at the end of this stage, the current will be set to fast charge value by the MCU.
T2-T3: Constant current stage. Charge battery with fast charge current, until the cell voltage reach up to 3.65V.
T3-T4:
Constant voltage stage. In this stage, cell voltage will be kept under 3.65V while charge current gradually goes
down. When the charge current is smaller than cut-off current(normally 1/10~1/8 fast charge current),MCU
terminated charge process and indicates full.

 

[Old_Scoot]

Hard to get a warm and fuzzy from Tenergy's documentation, right? They can't even label the alligator clips and tamyia connectors correctly in the photo in the manual (it is correct on the website).

As another way to check it, I had a look at the specs for Tenergy's 48v LiFePO4 battery pack. Not a lot of help there either. The pack doesn't give the internal specs. It does however give a maximum charge voltage of 58.4. That sure sounds like a spec for 16s battery.

Anyway, these Tenergy charges are cheap on ebay and are available from a US vendor so I'm taking a chance and ordering one. I don't think there will be any harm in connecting it to my 16s pack and monitoring it during the charge cycle.

 

[Russell]

That charger IS FOR 15 LiFePO4 CELLS...I know because I bought it for my 15 cell pack. A 15 cell LiFePO4 pack actually IS 48V nominal (15x3.2V) while the more common 16 cell pack we all call "48V" is 51.2V. I emailed All-Battery before I purchased it and asked about the output voltage because I had the same question given the range they spec but the charger rating plate says 54.7V. The 58.2V is the maximum open circuit voltage the charger reaches while charging. In practice my charger ends at just under 54.3V during a normal charge cycle but will reach just about 54.7V if I'm topping off the battery. The fan is also really loud, so much so that I replaced it. There is also no voltage adjustment plus unlike most other lithium chargers I've had the output will drop to a lower level, I forget the exact value, at the end of a cycle.


Oh yeah and they sell it cheaper on eBay;

http://cgi.ebay.com/Intelligent-2A-...emQQptZLH_DefaultDomain_0?hash=item4ce9222160

-R

 

[Old_Scoot]

The charger came in yesterday and I gave it a try. It charged my 16S headway pack to 53.7v which works out to 3.36v/cell as measured about 5-hours post charge. Russell, is that about the same resting voltage as your 15s pack? I'm not using a BMS, btw; waiting for Gary's new version to come out. I'm manually checking the individual cells with a voltmeter and plan to balance using a single cell charger as needed.

 

[Russell]

The charger came in yesterday and I gave it a try. It charged my 16S headway pack to 53.7v which works out to 3.36v/cell as measured about 5-hours post charge. Russell, is that about the same resting voltage as your 15s pack? I'm not using a BMS, btw; waiting for Gary's new version to come out. I'm manually checking the individual cells with a voltmeter and plan to balance using a single cell charger as needed.

I insert my Watts-Up meter in-line between the Tenergy 15-cell charger and the battery while charging and found during a normal charge cycle the indicator turns green when the voltage/current gets to about 54.27V/0.08A. At that point the charger voltage drops to 53.11V. I used it to charge my 15 cell LiFePO4 pack yesterday evening and early this afternoon it was sitting at 51.5V or 3.43V/cell.

When running without a BMS it's a good idea to use a charger set on the low side (~3.60V/cell) to avoid having some cells go too high but you do want to end up with all of the cells resting above 3.40V where they'll have 99.9% of their charge. Judging by an experiment I ran the other day I would estimate you are getting your cells to perhaps 95% full. That’s not too bad and it will at least pretty much guarantee no cell will ever charge too high if you started out with a balanced pack.

Single-cell chargers will usually charge to ~3.65V so either you’ll have to initially charge ALL of the cells with it or monitor the cell with a voltmeter and terminate the charge when say each cell gets to 3.40V (or whatever voltage you decide to use).

-R

 

[Old_Scoot]

Thanks for the insights. Yes, I think until I get a BMS this is a decent solution.

 

[dogman dan]

Oughta work. If you keep your discharge rates an depth of discharge lowish, they should tend to stay balanced anyway.

 

[Old_Scoot]

Thanks dogman for the vote of confidence. Most of my trips are just a couple of miles (small town).

 

[Russell]

I've got 15 cycles on my battery so far without a BMS and most rides are in the 70-80% DOD range with one at 87% with no problems. Having cells close in capacity is THE KEY to running a battery without a BMS. With a BMS you can get away with a low capacity cell since the BMS will keep it from charging too high or discharging too low but all it really does is cover up the problem.

-R

 

[Old_Scoot]

I've got about 5 cycles on my pack and so far so good. Most were only about 20% one was probably 60%. After one of the shorter runs 15 of the cells were 3.33 and one was 3.32. Good stuff these Headways.

Edited to fix a typo