Solar controller for LifePo4 batteries

[john61ct]

Originally Posted by Colin A

This does seem to work in practice. I have asked a few people in the electric propulsion biz about this and they seemed concerned that solar floating could be an issue. Basically they said longterm float with no discharge may cause capacity loss in the cells or loss of cycles.

Maine Sail has expressed the same concern, low float, say 13.2V, may cause reduced longevity.

We just don't know, and testing would take a lot of time and resources - what vendor would be motivated to prove this.

So best IMO is a battery monitor and relay that just turns the current off completely before full, ideally based on declining amps, rather than estimated SoC from counting AH.

The big advantage of an external device handling this is that it could be used for multiple charge sources, perhaps even diverting excess power to load dumps like charging a secondary bank or heating water.

[john61ct]

Originally Posted by SV THIRD DAY

This of it as charging when the battery falls below 13.3v and then stopping the charge once the voltage hit 13.3v.

But that's not actually **stopping** the charge source!

Keeping any charge source attached, especially at higher than resting voltage, is IMO bound to have **some** impact.

Originally Posted by SV THIRD DAY

I'm 3 YEARS on my current 400AH bank doing this and my last capacity check and top end balance done a few months ago showed no measurable loss in capacity.

But three years is nothing!

I expect if there is any harm from low-floating LFP, as opposed to shutting down the charge source completely, that may cause a well-maintained bank to last only fifteen years rather than twenty.

If it costs only a couple hundred and a little time to implement the recommended best practice for a bank costing thousands, that's what I want to do. Personally. . .

[Colin A]

Originally Posted by SV THIRD DAY

Some of the problem is in terminology...we should not use the terms Bulk, Absorption and Float when it comes to LiFePO4 batteries...the only reason we do is because that is the settings and lingo of the charge devices. But in reality you set them all at the same voltages, in my case here 13.3v. So don't think of it as "floating" your LiFePO4 battery. Using the term Float around LiFePO4 causes a kneejerk reaction and the lectures start on how to properly charge a LiFePO4 bank. This of it as charging when the battery falls below 13.3v and then stopping the charge once the voltage hit 13.3v. That's what I see from my charge sources...they are either charging when the voltage drops below the set-point of off when at the set point.

I'm 3 YEARS on my current 400AH bank doing this and my last capacity check and top end balance done a few months ago showed no measurable loss in capacity. That's real life data from a full time liveaboard set-up. Could I be crazy and my system a fluke? Sure...it's the internet and you see wild and crazy stuff and Fake News almost daily. All I can do it post what I know and have seen first hand.

I agree terminology is interesting. This was a European battery supplier that mentioned it. Basically he stated floating for a little while at a low setpoint was fine but he would not recommend it for more then a few days without discharge. As I recall he stated even the low voltage could create a heat problem in the cells degrading lifespan. Not a big deal for a cruiser but maybe an issue for long term storage (his recommendation was all charge sources had to be disconnected if left unattended more than a few days).

I know others that seem to agree that staying at a low voltage is fine. It's one of those things that causes a lot of confusion. Just looking online now at a few battery pack suppliers most still seem to recommend full disconnect. (other then the guys that say drop it in and it will be fine)
One exception may be lithioncs if I'm reading this right which calls for 3.4V a cell. (I may not be reading this right)
http://lithionicsbattery.com/wp-cont...e-Jan-2016.pdf

[alctel]

Originally Posted by john61ct

Maine Sail has expressed the same concern, low float, say 13.2V, may cause reduced longevity.

We just don't know, and testing would take a lot of time and resources - what vendor would be motivated to prove this.

So best IMO is a battery monitor and relay that just turns the current off completely before full, ideally based on declining amps, rather than estimated SoC from counting AH.

The big advantage of an external device handling this is that it could be used for multiple charge sources, perhaps even diverting excess power to load dumps like charging a secondary bank or heating water.

I think the 'no discharge' is the key there - IE long term storage.

A full time liveaboard would be running refrigeration etc which would def draw down the bank overnight.

[SV THIRD DAY]

Well that's interesting the charge has stopped according to my charge monitor battery monitor but what do I know go about your business nothing to see here....

For those that want the added complexity and added failure points of a top-end disconnect go out of head I never said you didn't need one or if you want one. What I've said is that I don't want one and don't think I need one and my test data has shown it's worked great so everyone can come off their Panic horse now and do whatever they want on their own boat and makes them comfortable.

[john61ct]

Originally Posted by Colin A

lithioncs if I'm reading this right which calls for 3.4V a cell. (I may not be reading this right)
http://lithionicsbattery.com/wp-cont...e-Jan-2016.pdf

From slide 13:

However, A BMS-to-Charger Control Connection is Recommended to Ensure the CHARGER is Turned OFF and Not the Battery (A Nuisance Factor)

Note the author and Lithionics system developer, Bruce Schwab @ Planet Ocean, is responsive to direct queries on such topics by email.

[john61ct]

Originally Posted by alctel

A full time liveaboard would be running refrigeration etc which would def draw down the bank overnight.

I agree but in principle for myself, I don't want general design guidelines to be driven by use cases that are bound to have lots of exceptions, different lifestyles an preferences, multiple charge sources, etc.

For that matter, if we're really talking not using the bank for a while, for longevity SoC should be kept right down at 10-20%

[Colin A]

Originally Posted by john61ct

From slide 13:

However, A BMS-to-Charger Control Connection is Recommended to Ensure the CHARGER is Turned OFF and Not the Battery (A Nuisance Factor)

Note the author and Lithionics system developer, Bruce Schwab @ Planet Ocean, is responsive to direct queries on such topics by email.

Yes it was slide 13 I was referring to. It shows two charge profiles one a constant voltage then a shut off and another showing 3.5v a cell then seemingly floating at 3.4v a cell (green line).

My issue is more the use my boat (and another I use and maintain) sees which is hanging on a mooring for several weeks at a time with no discharge (well maybe stereo memory which isn't currently hooked up) so I have some concern. Right now I don't have a LifePo4 bank and oddly this issue is one reason why, this is one of those issues where various experts seem divided and reading research papers doesn't seem to provide many answers as most of those assume shut off at full charge.

This is one of several issues that comes up in the marine electrical world with little consensus. Over the past 5 years I have talked to engineers from half a dozen different marine lithium suppliers and none seem to have a clear answer thou most seem to recommend disconnecting.

[44'cruisingcat]

Originally Posted by Colin A

This does seem to work in practice. I have asked a few people in the electric propulsion biz about this and they seemed concerned that solar floating could be an issue. Basically they said longterm float with no discharge may cause capacity loss in the cells or loss of cycles. It's hard to find any data about that thou. Honestly I come across this disagreement so much that I may buy a cell and see what happens if you have no load connected and float it for a few weeks at 13.3 or so.

Well, if floating at 13.3 might harm the batteries, set the float to 13.0 or 13.1. Or even lower.

The fact is, when my batteries initially go into float, set at 13.3, if there are no loads running the charge current goes to zero amps. Only when a fridge or other load starts, and the voltage drops below 13.3, does the charge controller start feeding current again. And only what the load is drawing.

But if I was leaving the boat with all the loads turned off, I'd set the float lower.

[john61ct]

The most important takeaway for me from all this, is that there is **no need** to keep LFP "full", even if your system's definition of that is 90%, and in fact it is harmful for them to stay that way.

Even for those of us who know this intellectually, it's a difficult lead-based thinking habit to break.

[thomm225]

Looks like a $35.00 Windy Nations Controller will work for you.

Mine will adjust down to 13.2 volts float.

[SV THIRD DAY]

Originally Posted by john61ct

The most important takeaway for me from all this, is that there is **no need** to keep LFP "full", even if your system's definition of that is 90%, and in fact it is harmful for them to stay that way.

Even for those of us who know this intellectually, it's a difficult lead-based thinking habit to break.

Absolutely!
It took me literally about a year to get comfortable with seeing 50 and 60% SOC on my bank and not getting panicky to start the generator. Getting out of the Lead mindset is perhaps harder than the actual LiFePO4 technology itself for us that grew up with Lead.

The other hard thing is to take general LiFePO4 comments and then apply it to the situation on your boat. I live aboard full time 365 and work from the boat all day long. I'm always here to watch my bank's SOC from the desk. If I leave for a few weeks, I just turn the charge sources off after getting the batteries at about 50% SOC. So what works for me might not work well for someone who is a 6 month on and 6 month off type cruiser and doesn't want to turn their charge sources off when they leave.

As a test, I just turned my voltage set point down from 13.3v to 13.1 and watched the amp meter go from 0.0A to -15A as the batteries were supplying my power loads until the lower set point was met. Then they would be held at 13.1v until I change it. So don't like 13.3v...no big deal...go lower. The important point is that once the batteries have reached the charge set-point voltage of your device, the solar controller or battery charger etc will stop charging. I've watched it happen for 3yrs now when my Amp meter will read 0.0A. The nature of charging with solar during the day and then drawing down at night is also an important point to remember. The bank is not going to be held constant unless either you are on shore power at a marina dock....but I'm on a mooring. But will be going to a Dock in La Paz soon so then I will have to mix up my strategy.

[john61ct]

Originally Posted by thomm225

Looks like a $35.00 Windy Nations Controller will work for you.

For a while, lots of negative feedback on those.

I've been picking up a bunch of 5A Eco-Worthy for $4-6 including shipping from Hong Kong for a one-per panel shade-tolerance scenario, since I know I'll need spares.

But they'll feed into a quality upstream controller/battery monitor,

I don't think it's worth saving less than a dinner trip to McD's with the kids, on something I'm trusting with my expen$ive LFP bank.

[thomm225]

Originally Posted by john61ct

For a while, lots of negative feedback on those.

I've been picking up a bunch of 5A Eco-Worthy for $4-6 including shipping from Hong Kong for a one-per panel shade-tolerance scenario, since I know I'll need spares.

But they'll feed into a quality upstream controller/battery monitor,

I don't think it's worth saving less than a dinner trip to McD's with the kids, on something I'm trusting with my expen$ive LFP bank.

I used a $12.00 controller with the lights etc on my first set of batteries and they lasted 6 years. It would allow a charge and float to 14.4. Those batteries were a Walmart Marine Starter Battery left over from when the boat had a diesel and an Interstate Deep Cycle Battery which were in parallel.

Looks like the price has dropped. I still have two of these for my 20 watt panels. I've had no problems with them

https://www.walmart.com/ip/Ktaxon-10...sem#about-item

I think I had maybe $200.00 in the batteries.

Now I have two $84.00 "deep cycle" batteries and this $35.00 Windy Nations Controller.

P20L LCD 20A PWM Solar Panel Regulator Charge Controller with LCD Digital Display and User Adjustable Settings=

So far so good but it does get lost from time to time and I have to reset it. I have the float voltage set at 13.6 volts

You do need to protect you investment though and I get that. I bought my boat and every thing in it for $2,000 so maybe I take chances from time to time with electronics, anchors, anchorages, and rigging, etc

This is my first monohull and it's a learning experience.........

[thomm225]

When I was using the $7.00 - -$12.00 controller I would let the battery charge until all the controller lights were on. (which usually meant 14.4 volts at the batteries)

If the lights were all on and the voltage on the panel side read say 19-22 volts, I'd then unplug the controller (and panel) from the batteries for a few days if I wasn't using the boat

Of course, you have to be near your boat to make this work and not be afraid of frying your controller.