lifep04 self build power station help

[mymorph]

hi,
i'm building a portable power station based around an acquired 40ah Valence lifep04 battery.
use: mainly camping so - water pump, fridge, lighting and charging devices etc. 2nd use, 12v high pressure air compresser for 4wd & general backup power

i'm not currently considering an inverter as i'm trying to keep build cost & size down, and i want it to be watertight.

currently we have 200 watt solar (2x100 panels) in parallel to PWM solar charger and the usual assortment of outlets.
fusebox & power metre inc a shunt will arrive shortly to complete the setup

i'm struggling with: in vehicle charging and what i need. can i just run a 12v supply from a cigarret outlet direct to battery? or need something like a
Cyrix-Li-ct 12/24V-120A combiner
or is that overkill and adds to cost?

thanks in advance

 

[Gazoo]

'm building a portable power station based around an acquired 40ah Valence lifep04 battery.

I have two of those batteries. I am using an AC 10 amp LiFePO4 charger and a Bestek 300 watt sine wave inverter. But I only use it for a backup for when the power goes out. Maybe the spec sheet will help you if you haven't read it yet.

http://mesa-tec.com/wp-content/uploads/2014/05/Mesa_Valence_U_Charge_U1-12RT.pdf

I would not connect the battery directly to the cigarette lighter outlet. Pretty sure the fuse would blow. What you need is a 12 volt DC to LiFePO4 charger imo. Maybe someone else will chime in with suggestions.

 

[mymorph]

thks, i got the battery for free, would love another 1 tho. that said my build will be small and versatile which really is perfect for my needs.

the in vehicle 12v charge only needs to be a trickle, 2 amps would be sufficient so as to not run down whilst travelling and powering the fridge. ive been looking at victron argodiodes and the Cyrix relays for charging 2 batteries systems. might be the best way forward? be interesting to see what others have done

basically i need to install a split charge system in the vehicle & connect to my power station via an Anderson. unless any1 has a better suggestion

how do the ready made solutions like the dometic pbl40 manage to charge with just the cigerette connection?

 

[Gazoo]

how do the ready made solutions like the dometic pbl40 manage to charge with just the cigerette connection?

They are using a DC to DC charger. I can't help you much with your design on the solar side. Whatever you do make sure you limit the current going to your battery from the cigarette lighter socket. I always charge mine to full at 14.6 volts and never let the voltage get lower than 11.5 volts. The BMS takes about 4 amps out of my battery per month and since I have two batteries that's a total of 8 amps. That's the only thing I don't like about these batteries so I charge them once a month so they will have plenty of capacity in the event of a power failure. I cycle them about every two months.

Have you looked at these?

12V DC Smart Charger (1.5A) for 12.8V LiFePO4 Battery Pack with 5.5x2.5mm plug

6532

www.batteryspace.com

These would work great for charging your battery from your cigarette lighter socket.

 

[mymorph]

thanks for that link, that looks perfect - just need to get it shipped to UK. i also need to capacity check this battery, as it was removed from a medical device as faulty. hence why i got it for free. ive charged it via solar without issue. it was at 10.5v when i received it. and tbh i expected it to not charge, but so far so good.

 

[mymorph]

update: Capacity test in progress,
battery as stated : 40ah (512w)
running themo electric cooler @48watts. (12vx4amp)

result: so far 8 1/2 hrs ~408watts or 34ah.

terminated test at 10.5v , BMS shuts down the battery at 10v so a little bit of juice left init.

remember this is a used rejected battery.

 

[Gazoo]

I assume you charged it to 14.6 volts?
What meter are you using to get your measurements?
34/40 = 85% capacity. 408/512 = 80% capacity. Since you are getting at least 80% capacity I would say you got a winner. Free is good.

You might try cycling it a few times to see if you can get a bit more capacity. When I tested the first one I got I had it hooked up to a 24' TV. I finally got the guts to hook it up to my 55" TV which of course draws a lot more power and I noticed I was showing more capacity on my meter. I averaged around 450wh with the first battery.

It wasn't long before I ordered the second battery. Interestingly it was missing all the labels and was basically dead...3.7 volts and no light on the battery either. I slowly brought it to life with a wall wart and when the light started to blink green I hooked up my charger which is 10 amps. Amazingly the capacity on that battery ended up being just shy of full at 505wh on my first capacity test at 10.5 volts, and 491wh on the second capacity test at 12.6 volts. Yes I was very relieved and happy and still am with both these batteries...lol. I bought them off ebay.

Then I hooked them in parallel and ran the same test and came up with an average of 995wh at 11 volts.

I need to make a correction about the self discharge. It's actually around 2ah per week.

Thanks for the update. You definitely got a gem.

 

[mymorph]

good point, it wasnt fully charged then. it was around 13.5v when i started my crude test . ive got it trickle charging currently will repeat the test

.

 

[Gazoo]

Then the internal batteries didn't balance either. The batteries balance as they reach their full state of charge of 14.6 volts. I would suggest charging it to 14.6 volts and then test capacity. Do this a few times. You should be able to terminate testing at 11.5 volts and still see more capacity than you did the first time. To get the most cycles left in the battery you don't want to go lower than 11.5. On the top end I always charge mine fully so the cells will balance. I forgot how many individual cells there are in these batteries but it did surprise me.

 

[mymorph]

i need a better solar charger, loooking at the victron 75/15 smartsolar. small enough physical size to fit in box, programmable to suit my battery and allows monitoring of the solar charge.

if a better solution exists which is cheaper and or better please advise, im happy to use simple circuit boards if 1 exists

 

[Gazoo]

I have never had a solar charger but I am sure you know Victron makes good stuff. I think Victron, EPEVER, Rich and Renogy are the popular ones from what I have read. But you made a good choice.

 

[mymorph]

breathing some life,
alot more work todo but the project is taking shape

 

[Gazoo]

Looks good from what I can see. What case are you building in? And did you decide on a solar charger?

 

[mymorph]

Looks good from what I can see. What case are you building in? And did you decide on a solar charger?

Fat 50 ammo case. cheap, strong & water tight. - got some custom made vinyl transfers to fit once the top coat has been sprayed.
as for solar charger it will be a victron smart mppt 75/15 when i see it at good deal.

regarding the valence battery, can you safely remove the 2 chunky battery link cables ? or should i just let them be. im not using them currently and they take up premium space.

 

[Gazoo]

Nice. The only reason you would need those cables is if you got another battery and connected them in series. Then the cables get connected so the internal BMS can communicate with each other. I have noticed many being sold with the cables cut off. Use a plastic cutter just to be safe or strip the insulation, or cut around it, and cut one wire at a time so there are no shorts.

 

[mymorph]

Custom water-resistant Anderson panel mounts