Lifepo4 charging

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Gareth Covell
Posts: 36
Joined: Fri Sep 14, 2007 4:43 pm
Location: Hereford

Lifepo4 charging

Postby Gareth Covell » Sat Nov 07, 2015 8:11 pm

Hi, I own a City-el vehicle which runs on 48v. These vehicles normally have three 110 ah lead acid batteries, a few years ago I added a forth lead acid battery which improved range and speed. I have now replaced this extra battery with four Lifepo4 cells of 60ah each. I am currently using a lead acid charger to charge them as the Lifepo4 charger I purchased was taking them to 14.9v. The problem with using a lead acid charger is that after reaching 14.4v it goes to float charge of approx 13.75v.
Float charging is said to be bad for Lifepo4's so I switch off the charger as soon as I can, this is very inconvenient. :x
Is there something I can get that could cut off the charger when it reaches the voltage I want? ( probably would aim for 14v ).
This could also act as a safety device should the charger fail to stop.
Something simple to fit and of modest cost is what I need.
Ideas please!
1999 City-el

glyndwr1998
Posts: 112
Joined: Wed Mar 06, 2013 12:34 pm

Re: Lifepo4 charging

Postby glyndwr1998 » Sat Nov 07, 2015 8:50 pm

Hi Gareth,

Try searching ebay for programmable combo meters, they are a voltmeter with built ibn relay cut off that uyoyu can program yourself, they also have a current shunt to monitor the current.

or, try some junsi cellloggers, I use these in my prius plug in conversion, youd only need one, plus a relay and alitlle transistor circuit, quite easy to do, endless sphere has loads of info on cell log cut off circuits, this will also give you cell monitoring.

both cheap and quite easy to install.

Anthony.

Gareth Covell
Posts: 36
Joined: Fri Sep 14, 2007 4:43 pm
Location: Hereford

Re: Lifepo4 charging

Postby Gareth Covell » Tue Nov 10, 2015 6:57 pm

Thank you for that info.
Could not find anything on junsi cellloggers.
Ebay has some programmable combo meters, don't know which is the best, but the cheapest one may do.
That one costs £16 item number 171523222609. They say it can switch on/off a rely(not supplied)to prevent over charging.
A circuit diagram it shown but not how it connects to a charger :? . Any way if you recon it will do what I want I will buy it.
1999 City-el

Gareth Covell
Posts: 36
Joined: Fri Sep 14, 2007 4:43 pm
Location: Hereford

Re: Lifepo4 charging

Postby Gareth Covell » Tue Nov 10, 2015 8:04 pm

I have now found the Junsi celllogger. Hobbyking sell them, they look interesting but so far I have been unable to find out how to make a circuit with one to cut off a charger. I can solder Ok, indeed I built the bargraphs but I had plans to work off.
1999 City-el

glyndwr1998
Posts: 112
Joined: Wed Mar 06, 2013 12:34 pm

Re: Lifepo4 charging

Postby glyndwr1998 » Mon Dec 28, 2015 8:49 pm

Hi Gareth,

I use both the cell loggers and volt combo meters in my set up.

I use the cell loggers to give me individual cell monitoring, this is the way I have my set up working. I have found that if driving a relay directly form the output port, sometimes this damages the small transistor inside th cell loggers, it then becomes useless for switching.
So, I use the cell loggers output port to switch a separate opto coupler, the switched Side of the opto then drives a 12v relay ok.
What I do, is lets say your monitoring 4 lifepo4 that'll be 5 wires going to th cell loggers, 0v, 3.2, 6.4, 9.6 then 12.8.
Tee into the 12.8v wire into the cell logger, and run that 13.2v to pin 1 via a 10k resistor of a 4n35 opto isolator. Pin 2 of the opto connect to the red wire from the cell loggers output port, no need to connect th black wire, the cell logger internals will give the negative and complete the switching circuit. That's the driver switch part done from the cell logger.
Get a 12v supply fused from your leaguer battery, and connect from th fuse via a 10k resistor to pin 5 of the opto, and a wire from pin 6 from the opto to your relay coil, neg from the relay coil back to the battery, circuit complete.
This gives isolation from th cell log circuit to the battery and switching circuit. If you have more cells just add more opto isolators wired the same way. Pins 3 and 4 are not used in this set up.
I personally have this circuit on my plug in Prius using 32 leaf cells in series, 260vdc, 8 cell loggers working in series.

Additionally, I also use a combo meter too, this is set just alittle higher than the when the cell loggers would trigger at max or min voltage, so, in the event of the cell log circuit failing for some reason like a stuck relay, the combo meter will trigger a separate safety relay and cut charge or discharge.

I also use same circuit in a home energy battery store using 7 leaf cells in series with a 6kva ups.

If you google cell logger circuit with opto isolators or opto couplers you should find a food circuit diagram. It's also on endless sphere website, that's where I got the info from. Th circuit has been working very well with no errors for about 2 years now. It's simple, effective, easy to rifts if faults occur and it's cheap.

Hope this helps.

Anthony.

glyndwr1998
Posts: 112
Joined: Wed Mar 06, 2013 12:34 pm

Re: Lifepo4 charging

Postby glyndwr1998 » Mon Dec 28, 2015 10:01 pm

For ease of set up just use a plug in breadboard to test the set up and operation, I used one, and been using it since, no components have moved or come loose, I should really build a purpose built pcb but as its been working so well and reliably I've left it alone, I have cut all resistors short and plugged in tight onto the breadboard for neatness.

Anthony.

Gareth Covell
Posts: 36
Joined: Fri Sep 14, 2007 4:43 pm
Location: Hereford

Re: Lifepo4 charging

Postby Gareth Covell » Tue Dec 29, 2015 7:43 pm

Thank you for all the information.
I have just got my hands on a combo meter sent from china. I struggled a bit with the instructions but I think I understand how to connect it. I now need to buy a relay, and some other bits and pieces, as well as a small box to keep every thing tidy.
Apparently you do not need a latching type relay with this meter as it will maintain the rely until reset. the output is 500ma at 12v. I have already set the meter to trigger a relay at 14v, but I cannot test this yet.
1999 City-el

glyndwr1998
Posts: 112
Joined: Wed Mar 06, 2013 12:34 pm

Re: Lifepo4 charging

Postby glyndwr1998 » Tue Dec 29, 2015 11:41 pm

Hi Gareth,

If it's similar to mine from China, it's got a title pcb with 6 connections, 2 for the shunt, 2 for the 12v relay supply, and 2 for the relay output.
Send the relay output wires straight to a relay coil, set your parameters, then press set on the combo meter, this will send 12v to the relay. Once the alarm set point has been reached by the combo meter, the meter will audible alarm and the 12v fm the combo meter will be cut and the relay will de energise. The combo meter will continue to alarm until you press set again to cancel the alarm. Press set again to send 12v to the relay coil and your ready to charge again.
Personally, I wouldn't trust my life or my battery pack solely on one though, I do use one but only as an emergency cut off in case the cell logger circuit fails for some reason. So I'm my case hopefully, the relay from the combo meter will always be energised, if it becomes de energised something has gone wrong with my celllog circuit.
Have fun setting it all up Gareth.

Anthony.

Gareth Covell
Posts: 36
Joined: Fri Sep 14, 2007 4:43 pm
Location: Hereford

Re: Lifepo4 charging

Postby Gareth Covell » Sat Feb 06, 2016 4:28 pm

I have now built my charger cut-off unit, I have set it to stop the charger at 14v.
I have tested it and I'm pleased to report that it works :D
1999 City-el


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