nut17 wrote:Thanks for the update Alga. I will persist with my existing controller for the time being (Terry's suggestion to disconnect the power from the panels then re connect seems to work) so I can wait for further developments. These http://www.trademe.co.nz/Browse/Listing ... ermanent=0 controllers are well priced and supposedly can be set to suit LiFePO4 so maybe a pair of these will do the job OK?
Cheers Chris
This is an MPPT controller, unless they have internal linking capability that makes one unit the control and the other units slaves you can only have 1 on a battery, 2 unlinked units will see each others input as battery voltage and adjust their charging regime to suit. Unless the back to boost is fully adjustable for both time and voltage you will be no off better than you have now. What if I build you a secondary control unit that will shut the supply off to the controller you have if a cell goes high voltage so you can reset the float voltage higher to ensure the battery remains fully charged without damaging the battery. This will reset the controller each time and get around the non return to boost problem without holding the cells a damaging high voltage.
bagmaker wrote:What voltage are you at @pepper? 12 or 24??
We tried them on 12 and 24v, it made little difference, but 24v did last longer. We are now trying 40a controllers in parallel to see how they handle lifepo4, an 80a PWM controller we tried worked, but it produced way less input than the MPPT and here in Tas, that makes a huge difference in winter. Now we are testing 2x40a MPPT with the same parameters and so far after 2 weeks not a problem, the cell balancers haven't started working, and the input seems very smooth, Using the 80a, near midday, the pack filled rapidly and cells went over 4v before the balancers could cut in properly. That has yet to happen with the 2x 40a controllers, but it is early days and things may change.
Another thing I've learnt with lifepo4, we've had a very cold winter so far, many morning well below zero and days hanging round 8-10deg. I have lifepo4 starters in our cars and about to put them in the earth mover and tractor, they are wonderful, but have a bug when it is very cold and you try to start the car, you get virtually nothing and the volt meter says they are at 12v. After many experiments, have worked out you have to put a short term high load on the battery for a few seconds and then it provides all you need instantly and the voltage instantly goes to 13.8-14.2v depending on temp So starting on very cold mornings, involves switching on the ignition and radio. turning the key for a second them letting it sit for 5 second, then doing it again and bingo it fires like the engine is warm. Different with the bus and house packs, as they have a constant draw and seem unaffected by the cool temps.
What you are doing is effectively dragging the cells down to a very low voltage and this causes the electrolyte to heat due to a lack of lithium ions available to pass from one plate to the other, this heated electrolyte then heats the plates till they are above 0 deg C, then they will release their lithium ions. The end result will be reduced cycle life. Heater pads are available and commonly used in the colder climates for electric vehicles, so if you need a high rate discharge from the Li cells, they need to be at 0*C or higher.
What brand cells are you using? Winston cells should be good for -10*C before these sort of issues appear, the yttrium in the compound gives a wider operation temp range than the standard LFP chemistry.
T1 Terry
A person may fail many times, they only become a failure when they blame someone else John Burrows
Those who struggle to become a leader, rarely know a clear direction forward for anyone but themselves
That sounds reasonable, don’t know how I would run a heater pad as I don't have an auxiliary battery in the Sahara, but could make one up from the spare cells I have.
native pepper wrote:That sounds reasonable, don’t know how I would run a heater pad as I don't have an auxiliary battery in the Sahara, but could make one up from the spare cells I have.
A trick I plan to try with the Mazda is to use a small motorcycle battery as the vehicle battery and simply switch the lithium house battery through for starting. The small lead acid battery acts as a capacitor for the alternator so when the house batteries se a high cell and cut the link, the lead acid battery is still there for the alternator to dump the last of it's current into to avoid a voltage spike and supply the voltage the feed back the alternator's voltage regulator is expecting to see, then it can taper back the alternator output as usual. Cheap, small and light weight, doesn't matter if it fails as the Li house battery is really doing all the work, just replace it when it starts to give off the rotten egg gas of a totally failed battery.
T1 Terry
A person may fail many times, they only become a failure when they blame someone else John Burrows
Those who struggle to become a leader, rarely know a clear direction forward for anyone but themselves
native pepper wrote:That sounds reasonable, don’t know how I would run a heater pad as I don't have an auxiliary battery in the Sahara, but could make one up from the spare cells I have.
They have updated their batteries since I bought this few years ago and mine is no longer there, but still works excellently.
How many of those do you have @pepper, what are you running. Each of the big ones is only a 20A/h battery............
Good for vehicle starting though
Got two, they are supposedly 40ah and 800cca. Bought a 400cca first as they said it would fire up the Sahara, but it failed on the first day and turned out it had a bad cell. Wasn’t convinced it would start the car without struggling, so updated it to the 800cca ones they were starting to produce and have worked wonderfully since. The only problem is the cold mornings, which after what Terry said was happening, want to find a way to overcome that. Have had them for close to 3 years now and they don't miss a beat, with heaps of power. Have even used it with a 600w inverter running an angle grinder and drill, it made very little difference to it at all, tested the voltage and it was still at 14v after about 20 minutes. Then it started the Sahara (turbo diesel) instantly. They have what they call a tune up thing you plug in, which is really an active BMS/balancer and been thinking of getting one to increase life span and to use it over night which may just keep enough heat in it to not have the cold problem.
As the cells are in metal cases, may even try putting insulation around the battery to see it it slows the cold ingress. Something like a battery cosy that can be put on at night to keep it warm enough to overcome the cold start syndrome , Bit of trial an error inmvolved.
Hmmm.....how would a 4 cell KFP battery still be at 14v after a load was applied for more than a few mins? Fully charged each cell is 3.4v, 3.45v is required to trickle charge the last little bit in, but 14v would be 3.5v per cell and that can only be maintained with a charge applied or rested after a saturation charge which really should only be performed when conditioning or reconditioning cells after a long storage period.
Something doesn't add up
T1 Terry
A person may fail many times, they only become a failure when they blame someone else John Burrows
Those who struggle to become a leader, rarely know a clear direction forward for anyone but themselves
My oh my, of course it doesn't add up, the 14v was meant to be 13v. As the top voltage setting is 14v and doubt it ever gets to that because of the charge regimes of the alternator, Using a grinder for 20 minutes would most certainly take a lot of energy out of the pack. The point was trying to make was, it still fired the car up instantly and could have turned over a V8 diesel engine probably. Compared to using a lead acid car battery of equivalent capacity, which I believe would struggle to turn the engine over after using a grinder and drill for 20+ minutes. Then again being technically challenged, I could be wrong.
13v sounds quite feasible, I have been capacity testing Brian's (Homeless) battery pack after 24/7 operation over the last 4 yrs and they are giving up over 60% of their capacity before the voltage drops below 13v under a 0.3C load. Unfortunately the battery copped a pounding a short while back when the solar charging failed (think it was a fuse fault) and the 24v to 12v DC to DC charger for the aux appliances dragged the battery down to 8v causing some of the cells to be reverse charged and destroying them. We have pulled all the battery packs apart and in the process of load testing to see what cells are still useable, some are still giving up 88Ah from 90Ah cells, not bad after 1500 cycles and some of them very hard cycles at that.
A person may fail many times, they only become a failure when they blame someone else John Burrows
Those who struggle to become a leader, rarely know a clear direction forward for anyone but themselves
13v sounds quite feasible, I have been capacity testing Brian's (Homeless) battery pack after 24/7 operation over the last 4 yrs and they are giving up over 60% of their capacity before the voltage drops below 13v under a 0.3C load. Unfortunately the battery copped a pounding a short while back when the solar charging failed (think it was a fuse fault) and the 24v to 12v DC to DC charger for the aux appliances dragged the battery down to 8v causing some of the cells to be reverse charged and destroying them. We have pulled all the battery packs apart and in the process of load testing to see what cells are still useable, some are still giving up 88Ah from 90Ah cells, not bad after 1500 cycles and some of them very hard cycles at that.