Maintenance Charging

[grizzzman]

During the day after the lifepo4 reaches its charged state, do you float (the wrong term really IMHO) at a lower level to harvest the unused solar for current loads? If so what voltage are you using? Is there proof that this will harm the cells?
Thanks in advance.

[T1 Terry]

If you have effective active cell balancing, the type that can move capacity from a high cell to a low cell rather than just turning on heater resistors to waste energy, then maintaining the 3.4v to 3.45v per cell is fine and can even be beneficial. Some like to use a "Hysteresis" charging principle where the charging stops at a given voltage and does not restart until the voltage drops to a preset level. This function is built into the Smart Victron MPPT controllers, the advanced user option needs to be selected to see the value and adjust it.
The Plasmatronics range also has an adjustable hysteresis (in the program 4 menu) that can be used for the same purpose. It is really only needed where the system is drawing very little energy from the batteries and mainly running on the solar, only using the batteries for the stray cloud and over night supply.
When powering say an air conditioner that can cycle "on" using more energy that being harvested from the solar but substantially less when cycled "off" allowing the battery to recharge, a hysteresis charging regime isn't really required, so that off set should be set to say 0.1v so the float voltage remains 0.5v either side of the target voltage .....

How many are now blinking their eyes like they have just come out of a coma

T1 Terry

T1 Terry

[Grandad]

How many are now blinking their eyes like they have just come out of a coma

Not me. Your proposition is dependant upon me trying to understand what you wrote.
I gave up on that years ago.

When the time comes, the answer to "Who ya gunna call?" is.....Margaret.

Problem solved.
No binking eyes or headaches.

Jim

[jon_d]

During the day after the lifepo4 reaches its charged state, do you float (the wrong term really IMHO) at a lower level to harvest the unused solar for current loads? If so what voltage are you using? Is there proof that this will harm the cells?

Grizz,

You want the float voltage to be as close to the bulk voltage setting. That way, the controller won't "switch' off between these two points.

1. When the controller has fully charged at the higher bulk voltage setting and switched off waiting for
2. The battery voltage to fall to the float voltage setting. And then switching back on and maintaining charge.

The bigger the gap in the 2 settings would mean that during the day, you're drawing down on battery charge. While this is not a bad thing, you're sort of reducing the effective "over night" capacity of the battery. (because the battery is being held at float voltage.... unless it drops back into bulk mode)

This is one of the downside of using a lead acid battery solar charger with 3/5/7 stages vs a lithium charger which should just be a "power supply".

[grizzzman]

If you have effective active cell balancing, the type that can move capacity from a high cell to a low cell rather than just turning on heater resistors to waste energy, then maintaining the 3.4v to 3.45v per cell is fine and can even be beneficial. Some like to use a "Hysteresis" charging principle where the charging stops at a given voltage and does not restart until the voltage drops to a preset level. This function is built into the Smart Victron MPPT controllers, the advanced user option needs to be selected to see the value and adjust it.
The Plasmatronics range also has an adjustable hysteresis (in the program 4 menu) that can be used for the same purpose. It is really only needed where the system is drawing very little energy from the batteries and mainly running on the solar, only using the batteries for the stray cloud and over night supply.
When powering say an air conditioner that can cycle "on" using more energy that being harvested from the solar but substantially less when cycled "off" allowing the battery to recharge, a hysteresis charging regime isn't really required, so that off set should be set to say 0.1v so the float voltage remains 0.5v either side of the target voltage .....

How many are now blinking their eyes like they have just come out of a coma

T1 Terry

T1 Terry

Funny that you mention "Hysteresis". I have my ElectroDacus SMBS0 set to 3.55 per cell the first charge of the day, then it keeps the SOC between 90% and 87% the rest of the day. This is what got me thinking about this issue. I believe it is my lead-acid mentality driving this but, when I’m camped in the trees it is a bigger issue. I have 3 1.2amp inductive balancers and a 5amp capacitive balancer. (due to a crappy Chargery BMS and not in use at this time) I have an additional 195-watt panel that I plan on installing. As the SBMS0 won't allow float settings I could set up a charge controller to 13.6 bulk and float and allow the DSSR20’s to divert to water heating duty when the set-point is met.
Oh and Terry my eyes are just fine.

[grizzzman]

During the day after the lifepo4 reaches its charged state, do you float (the wrong term really IMHO) at a lower level to harvest the unused solar for current loads? If so what voltage are you using? Is there proof that this will harm the cells?

Grizz,

You want the float voltage to be as close to the bulk voltage setting. That way, the controller won't "switch' off between these two points.

1. When the controller has fully charged at the higher bulk voltage setting and switched off waiting for
2. The battery voltage to fall to the float voltage setting. And then switching back on and maintaining charge.

The bigger the gap in the 2 settings would mean that during the day, you're drawing down on battery charge. While this is not a bad thing, you're sort of reducing the effective "over night" capacity of the battery. (because the battery is being held at float voltage.... unless it drops back into bulk mode)

This is one of the downside of using a lead acid battery solar charger with 3/5/7 stages vs a lithium charger which should just be a "power supply".

Thank you for your suggestion but I dont want hold the pack at 14.2 all day.

[T1 Terry]

Funny that you mention "Hysteresis". I have my ElectroDacus SMBS0 set to 3.55 per cell the first charge of the day, then it keeps the SOC between 90% and 87% the rest of the day. This is what got me thinking about this issue. I believe it is my lead-acid mentality driving this but, when I’m camped in the trees it is a bigger issue. I have 3 1.2amp inductive balancers and a 5amp capacitive balancer. (due to a crappy Chargery BMS and not in use at this time) I have an additional 195-watt panel that I plan on installing. As the SBMS0 won't allow float settings I could set up a charge controller to 13.6 bulk and float and allow the DSSR20’s to divert to water heating duty when the set-point is met.
Oh and Terry my eyes are just fine.

OK, the Electrodacus SBMS0 (Solar Battery Management System series 0.? I think it was 9 last time I looked) requires a game of trial and see the results Try setting the 100% cell voltage to 3.65v, watch where the cell voltages reach at the end of the 100% charge cycle .... over 3 days to a week of good solar charging.
If, at the end of the test period, none of the cells have run away consistently either during the 100% first of the day charge or during the the 90% top up charges, see what voltage reaches the end of the 90% top up charge, is it over 3.45v and how long can it hold it ..... If the 3.45v isn't reached or drops off to 3.38v or less rapidly when the recharge stops ..... then you need to try a slightly higher 100% charged voltage, try a cell voltage of 3.7v at the end of the 100% SOC charge cycle .... and go through the same test proceedure.
Furtunately, the SBMSO has a recording function .... this appears as though it needs more time to nut out than I've had spare recently, so if you have figured out how to drive and actually get a 7 day graph .... please share just how you did it The screen is so small on this latest addition, I can actually read what the settings are on the screen When I first set it up, everyone here had a go at logging onto it and now it won't talk to anyone, so it's sitting in the ice-cream container waiting for me to get another few hrs spare to try the whole process again ......
At the moment, my spare time is being taken up with testing a pair of iTech World120 batteries in parallel .... that is whole topic all of its own ..... Let's just say, the 120 does not indicate consumable Ah, even at a C20 discharge rate ...... and not even 80% of that ...

T1 Terry