240v 20amp charger linked to a 40amp solar charger

[native pepper]

I'm about to upgrade the solar panels on my bus, from 460w to 1000-1500w using 2x 40amp lifepo4 charge controllers for 1000w solar and would like to know if I can run a 20amp 24v charger and put it through my 40amp lifepo4 charge controller which is single stage bulk charge. If I go 1500w solar, will use a 60amp 240v charger.

Sadly don't have my late mate to pick his brain and after going through all his paper work and drawings, can't find anything that mentions this scenario as my setup will be a bit different to what most use I believe. I'll have 360amp of 12v gel batteries charged from the alternator through a 60amp dc-dc charger, which will mainly feed the hot water system, A/C and as backup. Along with that have 480amp of lifepo4 through 2x40amp lifepo4 chargers which will be fed by roof panels. If I decide to put 1500w on the roof, will use 2 x 60amp lifepo4 chargers and would like to be able to use a 240v charger when parked to keep the lifepo4 and gel full.

Just need to know if it's safe and good practise to use a 240v charger through my solar chargers so can feed the lifepo4 during many days without much sunlight. Could run the 240v charger direct to the lifepo4, but that would mean having to compete with lead acid parameter charging and use relay switches and voltage alarms, which in my opinion is not god for lifepo4 and so far, been unable to find a single stage bulk 240v x 12v 20-40amp charger.

Have had to fire up my veggie oil lister generator at home the last few days because of the lack of sun over the last couple of months down here and the wind generator doesn't to keep up with the demand when working in the workshop. The lister is so economical using veggie oil, to start and stop it, cost 39cents, as that's how much biodiesel it uses to clean the system out.

Has anyone used ultra capacitors in conjunction with a lifepo4 pack, found some notes from my late mate revolving around this approach, but the diagrams are missing, reckon his kids have them and not game to ask them for info as yet, things are still a bit raw in their households with unresolved family matters.

[T1 Terry]

The ultra capacitor charging requires very big mosfets to switch the current but the charge rate can be up to 10C in short bursts and voltage/temp sensing used to control the on/off cycle length, longer on when cold and deeply discharged, longer off for warm cells and close to fully charged.
Regarding the mains to lithium charging, better to do it via the DC to DC charger and connect the mains charger to the lead acid batteries, then you only need to control the DC to DC charger, the mains charger will look after the lead acid batteries. Not good to switch a mains charger with a PWM controlled regulator as the voltage surge between on/off/on has to go some where and that is up into the solar and then back into the charger, the return surge has lots of current with it and pops caps and diodes and does all sorts of mischief. The lead acid battery acts as a big capacitor, a lithium battery acts as an ultra capacitor, so if you want to go down the ultra capacitor track you can use a few of those new nano tech LiPo cells as the capacitor and a Schottky to prevent to surge running back up to the solar panels. A lot of hard work and not sure what gain there would be, but still an interesting project to fill in the idle hrs...... just wish I had a few idle hrs

T1 Terry

[Mrcoolabah1au]

I can give you some tonight just provide the candles after 12 midnight

[native pepper]

Thanks Terry, my lifepo4 charge controllers are MPPT, so may not worry about spikes. The dc to dc charger is connected to just the gel, lifepo4 is a completely separate system and haven't thought about whether to be able to connect gel and lifepo4 at some time. Can't see the gel being very useful for backup to lifepo4 when it is about 1/3 the usable capacity, but the gel have lasted a long time.

Regarding the capacitors, he says 2.7v x 3000f capacitors, connecting 5 in series and then paralleling them to get extra capacity. There's lots of maths and squiggly lines with notations, with the aim to drag as much energy from the sun late in the day when the lifepo4 pack is full, so the capacitors will take the majority of use overnight and have a full lifepo4 pack in the morning. Then the capacitors can take the load for most of the day and A/C and other heavy use appliances can be used constantly without taking much out of the pack. That's where my comprehension finishes, from there what he has written is gobbledy gook to me. He writes idea's like a business plan, lays them out in sequence of approaches and fills in the gaps, it's when you get past the original idea into the drawings, maths and weird notations that I come to an abrupt halt in understanding. He had his own form of notation, which doesn't resemble standard electrical notation and looks like some form of code.

I would have thought just getting another lifepo4 pack would do the trick, But he has weight and lots of other things he's taken into account, especially for RVs and marine where he has some diagrams of capacitor banks set up in lots of places inside for balanced distribution in really small places.

[T1 Terry]

The down side of super caps and ultra caps is the capacity, they can hold high voltage but not much as far as Ah. This is where the nanotech LiPo cells come into play as they can hold around 10 Ah at a higher than LiFeP04 voltage and let it go in up to 30C bursts, great for fast charging but fairly useless for extended capacity, better off with more Lithium capacity.

[native pepper]

Had visions of lines of capacitors lining the inside of walls of the bus or van and basically using those for use during the day and into the night before switching to the lifepo4. Considering I can't understand much of what he has written and lots of it seems in some shorthand code, which I know from experience he enjoyed making up, to keep ideas away from others and give his kids the shits. His kids are still trying to work out some of his work across the building industry, he tended to keep things to himself. His daughter who followed him into electronics and computing, just smiles and says that's my dad for you.

Thanks nice to know the facts, so will place it in the too hard box and pass it on.

[T1 Terry]

Building capacitor banks was really for the old lead acid battery days where they couldn't handle a fast charge rate, but if you had a very high current charger you could use them as a buffer to fast charge a battery bank, but not really something needed for house batteries, more for electric vehicle charging. I built one for lead acid battery charging a while back, the intention was to disulphate the plates with a surge current charging, but when I discovered lithium batteries 6 yrs ago the current flow was so high because of the high charge acceptance rate the solid state relays I was using soon let the smoke out, so did the cables because they failed in the closed state, so I gave that idea away. Even a 5 cell lithium battery charging a 4 cell lithium battery will flow well over 150 amps and make the cables smoke at only a 3v differential, they are greedy little buggers