Help with off-grid solar circuit

[Ampster]

Yeah, I’ll have to look into which controllers put out the necessary amps to charge my batteries, because I’m unsure if they generally output the same amps that are input?

Also, would more amps than 10% be beneficial to charge the batteries? Like, if the MPPT puts out the same amps as in coming in, could I set up my PV array to put out the max amps so I charge the batteries quicker?

I think it would be useful to familiarize yourself with what an MPPT charge controller actually does before you make assumptions. Good charge controllers can take a variety of Voltages and Amperage and deliver that power in the the form or the Voltage and Amperage that a battery needs for that particular phase of the charge cycle. The goal is to deliver the most power to the batteries. In simple terms the MPPT part of the controller finds the optimum balance of Voltage and Current in the panels at any time during the day. Those may change as the sun and clouds transit during the day.

The batteries, on the other hand need a very specific voltage to charge and that does not vary based on how much sun and clouds are available. Every battery pack also has a particular current where it can be charged most efficiently and that is what one needs to determine from the battery manufacturer to properly set the parameters in the charge controller.

Also there are several different phases of charge cycles and the Voltage and Amperage parameters that come out of the charge controller are different for each one.

If power (Watts) is defined as Amps time Voltage then the hope is that there is very little power lost as the MPPT charge controller changes the Volts and Amps that enter the controller to the Voltage and the Amps that are needed to charge the batteries.

[Superdoom]

I think it would be useful to familiarize yourself with what an MPPT charge controller actually does before you make assumptions. Good charge controllers can take a variety of Voltages and Amperage and deliver that power in the the form or the Voltage and Amperage that a battery needs for that particular phase of the charge cycle. The goal is to deliver the most power to the batteries. In simple terms the MPPT part of the controller finds the optimum balance of Voltage and Current in the panels at any time during the day. Those may change as the sun and clouds transit during the day.

The batteries, on the other hand need a very specific voltage to charge and that does not vary based on how much sun and clouds are available. Every battery pack also has a particular current where it can be charged most efficiently and that is what one needs to determine from the battery manufacturer to properly set the parameters in the charge controller.

Also there are several different phases of charge cycles and the Voltage and Amperage parameters that come out of the charge controller are different for each one.

If power (Watts) is defined as Amps time Voltage then the hope is that there is very little power lost as the MPPT charge controller changes the Volts and Amps that enter the controller to the Voltage and the Amps that are needed to charge the batteries.

Righto, so the charge controller does or can change the amperage that the batteries receive from the panels. That is cool... so I guess I just need to check my batteries’ optimum charging amperage and then see if my desired MPPT can charge at somewhere near but not above that amperage. That helps a lot, Ampster, thank you. I feel like I’ve got a handle on all this now!

[Ampster]

Righto, so the charge controller does or can change the amperage that the batteries receive from the panels. That is cool... so I guess I just need to check my batteries’ optimum charging amperage and then see if my desired MPPT can charge at somewhere near but not above that amperage. That helps a lot, Ampster, thank you. I feel like I’ve got a handle on all this now!

You have just begun. When you set up your controller, you will have to make some decisions about the 3 or 4 phases of charging batteries but that is a discussion for later.

[Superdoom]

You have just begun. When you set up your controller, you will have to make some decisions about the 3 or 4 phases of charging batteries but that is a discussion for later.

Righto, like Bulk, Absorption, and Float? If I got with the Victron 250/100 MPPT, there is no fourth phase. Would you recommend a fourth charging phase? I feel ya though, I need to figure out which voltages I should set for these phases. Any advice in that regard? I am planning to use the Trojan 2v 1,250ah smart-carbon FLA batteries, but are there general rules for the phases and voltages??

[Ampster]

Righto, like Bulk, Absorption, and Float? If I got with the Victron 250/100 MPPT, there is no fourth phase. Would you recommend a fourth charging phase? I feel ya though, I need to figure out which voltages I should set for these phases. Any advice in that regard? I am planning to use the Trojan 2v 1,250ah smart-carbon FLA batteries, but are there general rules for the phases and voltages??

I am not well versed in the details of Lead Acid batteries so you will have to get those parameters from the battery manufacturer or someone who is immersed in Lead Acid usage. I have been using Lithium batteries for 10 years and it is much simple with only two phases, the Constant Current phase (Bulk) and the Constant Voltage phase (Absorb). Float is only used occasionally with Lithium, and Equalization is never needed. I did learn Ohms law over 60 years ago and built a lot of Heathkit electronics back in the day.

[Superdoom]

I am not well versed in the details of Lead Acid batteries so you will have to get those parameters from the battery manufacturer or someone who is immersed in Lead Acid usage. I have been using Lithium batteries for 10 years and it is much simple with only two phases, the Constant Current phase (Bulk) and the Constant Voltage phase (Absorb). Float is only used occasionally with Lithium, and Equalization is never needed. I did learn Ohms law over 60 years ago and built a lot of Heathkit electronics back in the day.

Interesting... why is equalization never needed? Also, would float be potentially harmful to non-lithium batteries?

Anyone with expertise on lead acid batteries and bulk/absorption/float phases, please chime in!

[Mike90250]

Li batteries:
Cells need to be matched at the factory,
Cells drift much less than lead acid
the battery pack BMS does cell level balancing (good ones do anyway)
When they are full, further charging, even float, will damage them.

Lead acid:
sulfation
cell drift
cell degradation/plate material shedding into the sump
Less care in mfg, cells drift in capacity. Eq is easiest way to rebalance all cells in battery

[Superdoom]

Li batteries:
Cells need to be matched at the factory,
Cells drift much less than lead acid
the battery pack BMS does cell level balancing (good ones do anyway)
When they are full, further charging, even float, will damage them.

Lead acid:
sulfation
cell drift
cell degradation/plate material shedding into the sump
Less care in mfg, cells drift in capacity. Eq is easiest way to rebalance all cells in battery

Oh, okay. Very interesting. So would you say equalization (and float?) prolong the life of lead acid batteries? If so, how long can you expect out of a lead acid battery versus lithium?

[Mike90250]

Oh, okay. Very interesting. So would you say equalization (and float?) prolong the life of lead acid batteries? If so, how long can you expect out of a lead acid battery versus lithium?

That question is unanswerable. Say you and I drive the same car and tires, carrying the same weight, over the same route. A year later, you have burned thru a set of tires, 2 brake jobs and get 14 mpg. I'm on original tires & brakes and get 22 mpg. Which seat cover is better ?

Batteries are the same. Properly sized and cared for, name brand FLA batteries get 10+ years. I can put a cheap, undersized set of Li batteries on the twin of that house and they are dead in 4 years. Li are not, as the ads claim, magic batteries. They need a BMS, and controller & inverter that communicates with the BMS. And an educated owner.

There is a reason a power plant has a crew of engineers, maintenance workers and repair folks. Even with good gear, bad stuff happens and has to be dealt with, it's not simple plug and play.

[Ampster]

Oh, okay. Very interesting. So would you say equalization (and float?) prolong the life of lead acid batteries? If so, how long can you expect out of a lead acid battery versus lithium?

Some lithium battery manufacturers have guaranteed 10 years. By law EVs have a 10 year warranty with 20% degadation.

[Mike90250]

That warranty is worth the paper and ink making it up.

Just bought a phone battery from Amazon, 12mo warranty. 4 months and it's dead, vendor offered me $5 Whoo Hooo

Motorola Droid Turbo Battery 3950mAh (Upgraded) SHENMZ SNN5949A EQ40 Battery Replacement for Motorola Droid Turbo XT1254 XT1225 with Tools | Motorola EQ40 Replacement Kit -12 Month Warranty Sold by: AexPower

It takes one line to say "10 year warranty", and yet the paper work is 5 pages or more, of things excluded in the warranty. Buyer beware.

[Superdoom]

Some lithium battery manufacturers have guaranteed 10 years. By law EVs have a 10 year warranty with 20% degadation.

Dang, I would say they probably aren’t worth the price then for only 10 years. They might last longer, though? Lead acid still seems simpler than lithium in regard to setup.

[Ampster]

Dang, I would say they probably aren’t worth the price then for only 10 years. They might last longer, though? Lead acid still seems simpler than lithium in regard to setup.

You opened the door for this Lithium fanboy to rant. As far as your application there is more support on this Forum for Lead Acid.

However there are also economic reasons why Lithium batteries are used in EVs, in large grid support battery systems and in home battery storage such as Tesla Powerwalls, SolarEdge StorEdge with LG Chem batteries and the new Enphase battery product. I tend to be guided by the decisions the big money is making as long as I can understand the technology.

[Superdoom]

You opened the door for this Lithium fanboy to rant.

Haha, hey I’m not saying I didn’t enjoy the rant! It is good to weigh up the options, but I’m the kinda fella that does this as simply as he can. Though, I may search for a MPPT with a equalization phase now because it would seem like a good idea for lead acid batteries. Is this ‘smart carbon’ business a gimmick or valuable innovation?

[Ampster]

.......Is this ‘smart carbon’ business a gimmick or valuable innovation?

My personal opinion is it is an attempt by the traditional Lead Acid manufacturers to rebrand 100 year old technology to compete with Lithium.

Lead Acid manufacturing and Lithium battery manufacturing require significantly different processes so I do NOT think those Lead Acid manufacturers will retool to make Lithium. In addition, with the exception of Tesla and Nissan most of the Lithium production capacity is in Asia. The European auto manufacturers are scrambling to build battery capacity.

There is a huge disruption on the horizon, but I can't tell you if it is next year or next decade. I am too old to waste my time on old technology but for younger people they can afford to learn about the fundamentals using Lead Acid because it is is still the least expensive. By the time they burn through their first pack there will be a lot more cost effective choices.