Home assemble LiFePo4

[Derekoak]

I suspect it is only significant at southern Altitude. But we go there frequently. But even so it may be not worth the bother.

 

[Sprinter 1 cup]

Thats why I done the thread on low voltage charging but no comments as yet ! as my winter set up,solar harvest is less than 1 amp a hour. Victron shunt dont registered at that voltage. 0.800 ma
Only b2b and hook up need heating when used ! ? . I don't think my 200w solar is a killer at frozen temps in this country.
The ring charger dont turn off like the orion, or will in the settings.
, mate is it that much difference in temp somerset is not that cold yet.we are still above 5 degrees . So no alarms gone off yet .lol

 

[Derekoak]

We are 200m up in Lancashire, but it is not cold today. I know where we go it is often cold enough to need heaters but to your question, My bms just does not seem to allow charging when the temp drops below threshold so I have no option. I also have no information whether a small rate of charge is allowable. I do not wish to risk my batteries to find out.
I have an idea how to get battery heating from solar but it would cause a small continuous battery drain as the wiring would need the temperature sensor on all the time rather than just on ignition.

 

[Sprinter 1 cup]

If the bms locks out charging at 0 degrees, will bms still let fridge work ? Ie is there still an output ? If relay clicked.
As know one said eiva way . They just seem happy it worked in the videos. Stopped charging that is.
Im think like an manual reset or automatically restarts the relay for output. No vids have shown the output at the safety cut out time.!

 

[Derekoak]

The bms has separate charge and discharge mosfets. Both controllable manually and or automatically to temperatures so with charging off, as below charging low temp setting, the battery still runs the fridge as long as you are above the discharge low temp setting. It will not do what you want that is stop charging below a temperature, except a trickle.

 

[SquirrellCook]

It's good to know that the fridge won't thaw out if it's at -10 deg. C

 

[Derekoak]

I have successfully heated my battery from cold until the bms were satisfied and charging began. I know now that my pads take 12 amps whilst heating. My bms will be set to 5C but they have a lag so must be heated to 10C to loose the low temp fault setting. My cells under my heating regime are about 1 degree C cooler on the none heated side compared to the top of the heated side. So it is best to site the bms thermistors ontop of the heat pads. My heat pads are between each pair of 100ah cells.
It took 9 minutes to heat the cells from 6C to 10C using about 2Ah of battery. If the ambient was just 5C it would take about 11 minutes to get to charging temp. If the ambient was 0C it would take 22 minutes.
I have set the w1209 temp switch to a backlash of 6.5 degree, with a temperature to switch off the relay of 12C. That means that it will instigate charging at 5.5C to ensure it is set before the bms go to fault at 5C. When I switch the ignition on charging will begin and switch off at 12C by which time the bms sensors will be at 10C and ready to charge. Then I can start the engine to recharge immediately. Only the first relay coil will drain the starter battery, all other load is from the leisure battery. I will gain back the 2Ah of heating loss from the batteries in just over 2 minutes of running the engine.
I can still use my ring solar controller for solar, but it cannot charge or heat the batteries when it is cold. I will see how often there is enough solar charging opportunity lost before I try to deal with that.

I have discovered a fault with my logic. Last night the battery temperature just dipped to 5C. One only bms went to low temp fault. It will stay there until 10c or until I manually reset it. It was 8 C when I switched on the ignition hoping to start heating. Of course my temp sensor from the switch had missed the below 5.5C period so at 8C it saw no need to heat.
So either I need to rewire the temp sensor to be always on, a power drain of around 1ah per day all year, or I must reduce the temp backlash to say 1.5C so that it switches on heating at anything below 10.5C (at ignition on) and switches off at 12C ensuring that the bms will be able to charge, whatever the temperature at ignition on. That means I will heat much more frequently but the new heating occasions may only be perhaps 1ah. Just before I have ample recharge available. Decisions?

 

[SquirrellCook]

I have discovered a fault with my logic. Last night the battery temperature just dipped to 5C. One only bms went to low temp fault. It will stay there until 10c or until I manually reset it. It was 8 C when I switched on the ignition hoping to start heating. Of course my temp sensor from the switch had missed the below 5.5C period so at 8C it saw no need to heat.
So either I need to rewire the temp sensor to be always on, a power drain of around 1ah per day all year, or I must reduce the temp backlash to say 1.5C so that it switches on heating at anything below 10.5C (at ignition on) and switches off at 12C ensuring that the bms will be able to charge, whatever the temperature at ignition on. That means I will heat much more frequently but the new heating occasions may only be perhaps 1ah. Just before I have ample recharge available. Decisions?

I'm glad I'm not there yet, work has gone silly. Unfortunately that pays the bills. I guess I'll be needing more pennies when I start the self build electric motorhome

 

[Derekoak]

If the French let us travel we we will go south as is. The battery works fine. If it is below 5.5C at ignition on then the heat pads work and charging happens, if it is between 5.5 and 10, I can manipulate the bms settings to allow charging. Its just not ideal.

 

[Sprinter 1 cup]

Pretty smart app real time tracking and fine tuning. My re-lion bat is dumb no bluetooth or temp. I have to relie on the victron 100/30 solar controller for both, at 20 below I would just pray with my beenie on, in the dark !. as horrors aways comes after dark lol.

 

[Nabsim]

Not sure if I have missed something but does your set up not work in the same way commercially built Lifepo4 battery do? I can put as much charge as I can throw at them realistically down to minus 5, from minus 5 to zero I can still charge but at a reduced rate. In any event I can carry on discharging safely to minus 20

 

[Derekoak]

Not sure if I have missed something but does your set up not work in the same way commercially built Lifepo4 battery do? I can put as much charge as I can throw at them realistically down to minus 5, from minus 5 to zero I can still charge but at a reduced rate. In any event I can carry on discharging safely to minus 20

If you are talking to me, I guess you are, then the answer is no. I set the low temp charge cut off to 5C when the sensor notes a temperature below 5 it goes into a low temp fault mode and no charge can come in. I have tested that with a clamp current meter. I can still use the battery as there is a different low temp discharge setting that I set to -20C.
Unfortunately when the temperature rises above 5 it does not come on again until 10C. That means that to automate heating I must heat above 10C to get rid of the fault setting . Manually if the temp is above 5C, I can change the low temp settings temporarily to say -1C then the fault disappears and charging begins. I can reset to 5C immediately for battery safety.

 

[wildebus]

Not sure if I have missed something but does your set up not work in the same way commercially built Lifepo4 battery do? I can put as much charge as I can throw at them realistically down to minus 5, from minus 5 to zero I can still charge but at a reduced rate. In any event I can carry on discharging safely to minus 20

A good BMS will have a setup where it will not allow a charge current to come into the battery when it is below a selected current. If you have that feature, then there really should be no need to add in external circuitry to disable or disconnect chargers.
Better BMSes will also allow a small current (typically under C/10 - or under 10A per 100Ah) to go into the battery at below 0C temperatures as that is ok, and as you describe your batteries allow (the C rate may be different of course - and maybe have the -5 and zero round the wrong way in your post?)
And then there are batteries with BMSes designed for use with heating pads which will, when neccessary, divert the charging current into the pads to warm up the battery to a point where it is safe to start charging properly (these are the batteries that "charge down to -20" but don't really - they ACCEPT charge current and that current goes to the heaters to warm the cells up in order to take a charge).
The above is what you (or at least I, anyway) expect and want to see in a commercial Lithium Battery.

The only time I believe you need to start messing around with external temp sensors and disabling chargers (INCLUDING enabling low temp disconnects on a Victron Solar Controller) is if your BMS has no reliable low-temp disconnect.

One additional problem with disabling chargers is that you are cutting out extra available power to your leisure system as a whole. If for example you have a demand of 10A and your solar could bring in 5A, by disabling the controller you are depriving yourself of 5A of current that wouldn't be going to the battery anyway (as the demand exceeds the charger output). The same would be true of a B2B or a Mains Charger that you disable due to temperature. You lose all the potential power from those sources and could end up relying on a battery solely for power even if hooked up until it has warmed up sufficiently.
It is a much better idea - IMHO - to fit a BMS that manages the charging disconnects internally, or if your chosen BMS does not have that ability, to not attempt to control the chargers, but use a temp sensor to control a power relay to cut the charging circuit TO the battery and just leave the load circuit FROM the battery active (would be a little more tricky with something like a Victron Multiplus to do that, but it is possible).

 

[Derekoak]

It is a much better idea - IMHO - to fit a BMS that manages the charging disconnects internally, or if your chosen BMS does not have that ability, to not attempt to control the chargers, but use a temp sensor to control a power relay to cut the charging circuit TO the battery and just leave the load circuit FROM the battery active (would be a little more tricky with something like a Victron Multiplus to do that, but it is possible).

I agree with what you say. We were talking about a victron mppt and you said that cutting the mppt output away from the battery and diverting it's output to battery heaters as you describe here would be a use as a power source rather than a battery charger and would invalidate the guarantee. Were we talking at cross purposes?
It is relevant again as my ring b2b is throwing another wobbly and I might give up on it.

 

[wildebus]

I agree with what you say. We were talking about a victron mppt and you said that cutting the mppt output away from the battery and diverting it's output to battery heaters as you describe here would be a use as a power source rather than a battery charger and would invalidate the guarantee. Were we talking at cross purposes?
It is relevant again as my ring b2b is throwing another wobbly and I might give up on it.

No, it wouldn't invalidate the guarantee/warranty. What Victron says is that it can be used that way but they won't guarantee it will actually operate successfully for everyone.

Oddly enough I was looking up some info on the MPPTs the other day and came across an interesting statement as part of the Intro for the controllers on their website... https://www.victronenergy.com/solar-charge-controllers/smartsolar-mppt-75-10-75-15-100-15-100-20
"The SmartSolar charge controller will even recharge a severely depleted battery. It can operate with a battery voltage as low as 0 Volts, provided the cells are not permanently sulphated or otherwise damaged."

The "... It can operate with a battery voltage as low as 0 Volts..." I found especially interesting being stated so up-front (which suggests it works well?) and I have operated them like that in effect when isolating the battery bank but not turning off the solar controller (useful to provide lighting when working in the electrics cupboard without the batteries in-line.

 

[Nabsim]

Not sure if I have missed something but does your set up not work in the same way commercially built Lifepo4 battery do? I can put as much charge as I can throw at them realistically down to minus 5, from minus 5 to zero I can still charge but at a reduced rate. In any event I can carry on discharging safely to minus 20

Sorry folks, not sure if I had missed my meds when I typed this but I made a glaring error each time I put minus 5, it should have just been plus 5 then reduced rate charging to zero and safely discharge to minus 20.