Solar charge controller, what for?

[Living Large]

I'll leave the lead to other threads, but just goes to show you I'm no lifepo4 fanboy, but man, can I relate to your wow factor. Everyone who actually goes hands-on goes through it.

This is actually something I expected based on the research I did on this site. When I saw the consequence of low insolation in my area, I envisioned my generator running 6-8 hours a day, which is totally unacceptable to me.

My estimates for an LFP solution were 2-3 hours. To me, that is a WOW difference. Having a stable source with a flat discharge curve just clicked for me.

I guess I am arguing that I did in fact see a wow factor in my spreadsheet and in print. The price is a wow factor too, a negative one, but I am willing to pay the premium for usability and lower maintenance and peace of mind. Others may find more peace of mind with keeping half the cash in their bank account - which I can understand. Each to their own.

[solar pete]

AFL fan, cool. My team is Collingwood. Unfortunately they are not having their best year. I may be biased having grown up in Melbourne , the home of AFL, but I think it's the best "Football" game to watch. Mostly.

Mad Port Adelaide fan here, we are having a bad run this year, oh well there is always next season

[bungawalbyn]

AFL fan, cool. My team is Collingwood. Unfortunately they are not having their best year. I may be biased having grown up in Melbourne , the home of AFL, but I think it's the best "Football" game to watch. Mostly.

[PNjunction]

Perfect! Oh man, so many choices. Run more gear? Re-purpose a panel or two for another purpose? Become a 10% psoc pioneer like 40-60 soc?

I catch a few AFL games on Saturday nights here, and forgot about the seasons - people somewhat bundled up in the stands, sun going down at 5:30p local or so. Looking forward to the Grand Final in October.

[bungawalbyn]

Wow - you have the luxury now of figuring out how much more you can power with it. OR, ask this question again in December, when you may have very little solar insolation! Think twice before removing those panels. What I'd do now, is just run in a lower psoc window and basically have the cells consider your needs as a mere aggravation.

Hi PNJ,
I have to fiddle with the settings a bit when I can eliminate the voltage drop on the board, or reroute the cell sensor wires to get a truer reading. Other than that all seems to be working as designed.

As to sun in December, I'm in Australia, December is summer. Its winter here now. SHORT DAYS

[PNjunction]

With all the panels hooked up I'm getting about 65 amps, which runs the batteries up to my HWS diversion cut in about 1 hour after the sun hits the panels.

Wow - you have the luxury now of figuring out how much more you can power with it. OR, ask this question again in December, when you may have very little solar insolation! Think twice before removing those panels. What I'd do now, is just run in a lower psoc window and basically have the cells consider your needs as a mere aggravation.

The efficiency of the LIFePO4's harvest and return of power has caught me a little by surprise. On the FLA's I was struggling to keep up with usage in fine weather, now I'm looking at taking panels out of the array. I got them because of their promise of efficiency, but how much difference that has made is amazing.

This is the WOW effect that can't be reproduced on paper or in a forum. Kind of like describing to someone how riding a Harley Davidson feels like. You can't - they have to experience it for themselves. Or pilot a large radial-engine prop plane.

If you run lead as a standby / backup like I do instead of lifepo4 for daily cycling, consider a pure-lead agm now that you are addicted to efficiency. The internal resistance of even a conventional agm is twice the rate of fla (0.10C vs 0.25C typical, which means less time charging), and of course pure-leads which are even more efficient / faster to charge.

I'll leave the lead to other threads, but just goes to show you I'm no lifepo4 fanboy, but man, can I relate to your wow factor. Everyone who actually goes hands-on goes through it.

[bungawalbyn]

With all the panels hooked up I'm getting about 65 amps, which runs the batteries up to my HWS diversion cut in about 1 hour after the sun hits the panels. As this amperage is less than HWS element pulls this means the HWS is cycling. I've adjusted it so the cycling is not rapid, but it does draw on battery power to make up the difference. Oddly enough it should work better as the sun comes up towards summer and the amps increase.

The efficiency of the LIFePO4's harvest and return of power has caught me a little by surprise. On the FLA's I was struggling to keep up with usage in fine weather, now I'm looking at taking panels out of the array. I got them because of their promise of efficiency, but how much difference that has made is amazing.

The HWS just turned on, 1 hr into charging!!! Maybe I'll go get an air conditioner for summer.

[bungawalbyn]

It may be off topic, but had to say this up front - you ARE going to use a controller too right? Conventional wisdom has people popping small panels on their Pb batteries without them, and this works as long as you are CYCLIC duty with them, but in a fully-charged float / standby - NO WAY. Even a dinky panel without a controller on a fully charged or nearly fully charged battery will have them trying to reach 18v or so. Bad news and dangerous obviously.

back to our regularly scheduled program..

Yes Yes Yes. It's all still in place. Just have to make a few adjustments as I have pirated some bits for the new system.

[PNjunction]

I'm thinking of leaving one of my old FLA sets at the house doing what they like best, being an ornament on float, for emergency bad weather or what ever other reason. I'll give them a panel to keep them floating.

It may be off topic, but had to say this up front - you ARE going to use a controller too right? Conventional wisdom has people popping small panels on their Pb batteries without them, and this works as long as you are CYCLIC duty with them, but in a fully-charged float / standby - NO WAY. Even a dinky panel without a controller on a fully charged or nearly fully charged battery will have them trying to reach 18v or so. Bad news and dangerous obviously.

back to our regularly scheduled program..

[PNjunction]

Ack - I promise to clean up my responses when I am once able to edit my replies. Guess they are still working on that.

[PNjunction]

So far PNJ, my problems seem like they are more in the likelihood of overcharge. 3.0V is 12V in the pack, that's way low.

Actually, you are correct for a low-current application like ours! So much talk of high current EV that even I get it wrong.

To be totally conservative, a value of just under 12.8v is when the discharge slope starts to dive - shallow, but if you like 12.75 would be fine with our low current application.

On the small side, consider that a smart lifepo4 charger, the Tecmate Optimate Lithium TM-291 12v/ 5A charger considers 12.8v to be the 80% DOD *rested* value, and anything lower than that gets the .01C "climb out of the discharge knee slowly" effect, until about 12.8v is reached whereupon it applies full current.

I tested that on both powersports and my own larger prismatic banks (12.75v lvc), and from a 100% SOC charge (which I don't normally do!), I was able to get 80% of the rated value from the bank when measured on a West-Mountain CBA-IV computerized analyzer setup - and compensating for the test-leads too with my Fluke 87V as the final say.

Small potatoes, but I was glad to see that 12.75v was as low as I'd ever like to go for maximizing cycle dod's. The low-current revival when under this value was an eye-opener which makes total sense.

My analogy (love those even if far-fetched) is like scuba diving - go too deep and you better come out slow or you get the bends.








At present current usage in the last couple of days, I've gone down to about 13.24 rested overnight (except for fridge +inverter). And run up to cut out at about midday. That's on half my panels, 6 weeks from the shortest day. You seem to be able to get a lot of power out of these with little voltage drop when you get to around 13,2V.
I have yet to take them below that (rested) or about 13.15 under light load.

I'm thinking of leaving one of my old FLA sets at the house doing what they like best, being an ornament on float, for emergency bad weather or what ever other reason. I'll give them a panel to keep them floating.

I drive my systems carefully[/QUOTE]

[bungawalbyn]

So far PNJ, my problems seem like they are more in the likelihood of overcharge. 3.0V is 12V in the pack, that's way low.
At present current usage in the last couple of days, I've gone down to about 13.24 rested overnight (except for fridge +inverter). And run up to cut out at about midday. That's on half my panels, 6 weeks from the shortest day. You seem to be able to get a lot of power out of these with little voltage drop when you get to around 13,2V.
I have yet to take them below that (rested) or about 13.15 under light load.

I'm thinking of leaving one of my old FLA sets at the house doing what they like best, being an ornament on float, for emergency bad weather or what ever other reason. I'll give them a panel to keep them floating.

I drive my systems carefully

[PNjunction]

Re the LVC:

Even though the graphs for Winstons show them going down to 2.5 or 2.7v do not be tempted to go that low, especially since you are not discharging at massive current levels like an EV. 3.0 to 3.1v per cell is what I'd shoot for as an lvc, and of course does not mean you have to go there all the time.

Other cells like A123 seem to be able to survive going that far or further, but we are not sure if the Winstons will handle a similar regime with long life. Despite their testing down to 100% DOD, what we DON'T know is how they charged them back up.

Did they just hammer them at deep discharge, or did they wisely control the climb out of the steep knee with a *shallow* charge current until the cells climbed out of the knee, to maybe 3.1/3.2v and THEN followed up with normal current levels?

This is what I caution people about, and wonder if EV'ers using prismatics do the same? I doubt it. Intercalation on recharge while in the steep part of the knee is inefficient compared to the rest of the normal slope, so if you don't want / have the ability to control current to about .05C or less while coming out of the deep part of the discharge slope, then a 3.0 / 3.1 / 3.15v (take your pick) is a good place to stop for an LVC.

These are rested voltages of course, so take into account the amount of current you are pulling when approaching the lvc. If high, then the lower 3.0 may be appropriate. (EV'ers choose ones even lower). If you are tickling them at .1C, then perhaps stop at the higher voltage.

Surprisingly, if you look at it from a 100-80% SOC level, then stopping at approx 3.0v yields 80% of the cells rated capacity. But, at the top end we don't want to go that high on a regular basis, so chop 10% off the top, and now you have about 70% rated capacity.

This is just me approaching it from a conservative standpoint, and also taking into account that prismatics may not be as robust as an A123 cell.

[bungawalbyn]

I finished wiring in the 12V to 240V relay to operate the HWS. I had to isolate it from it's original circuit and run a new line through the bathroom back to the control board.
This afternoon the voltage started the rapid rise again and the relay kicked in at the right level. Owing to the voltage drop between battery and V sensors the gap between high and low is artificially reduced, so I had to drop the LV point to stop it cycling. This is on half my panels charging at 35 amps.
Tomorrow I will hook the rest of the panels up to the system and see what it does. I expect the batteries will top up in about half the time.
When it comes to switching on the HWS load dump, the voltage drop should be lower as the total panel output is a fairly close match for the HWS element. It SHOULD work much better, and run the HWS mainly from the panels. If that's the case I'll bring the on off points closer together again.

[bungawalbyn]

I think I am starting to be impressed by the efficiency of these batteries.

After running half the house circuitry and half the panels through them, yesterday they hit the knee. They stayed at around 13.2 to 13.3 for 2 days then at first slowly rose to around 13.4 then fairly quickly went up in V from 13.5 to 13.7 in about 15 minutes. This is at 35 amps. This tripped the HWS relay (Not yet wired up to house) So that is working. Will have the HWS relay wiring finished today so it will be amusing to see how that all works.

After it ran up to the high V I switched the whole house over to the LFPs and this morning they were at 13.24V. This seems to be about where they sit happily taking and giving heaps of charge.

We are only 5 weeks from shortest day, so I'm wondering if I will need all my panels to power this setup.