Some quick questions about charging agm batteries

Lumisol

I will be using a tristar mppt 30  controller to charge my 6 volt agm batteries (48 volt bank).
The battery specs for charging say:

25A @ 1.75/Cell	500Min
75A @ 1.75/Cell	125Min

Recommended Charging Options:

• AC Chargers: Any Quality Brand AGM- Smart & Microprocessor controlled- charger with the recommended specs above can be used. Battery Charger Guide.
• Solar Panel: 175W-450W (120W may be used if Depth of Discharge would not exceed 50%).
• Wind Turbine: 175W-450W
  

* Warning: Do not use a charger with smaller amperage than the recommended Charging Current shown above. 
                  Maintainers should ONLY be used to maintain a fully charged battery but NEVER as a charger.

Operating Temperature Range:

• Discharge: -4~140F
• Charge:     14~140F
• Storage:     -4~140F

Temperature Compensation:

• Cycle use:     -15mV/C 
  
• Standby use: -10mV/C 

I will be using the system from May to October generally and 1 or 2 times a month at most. Should I just flip everything off during the off season months and not try to keep the batteries charging at that time since they may get to temps lower than the 14 degrees F they should be charged at.

Does the controller have a setting for this minimum charge temperature (I got the temperature sensor for it)?

Does it have settings for the 

25A @ 1.75/Cell

500Min

charge rate?
I have not set one up yet and do not know what the settings will be so any help anyone has would be great.

What does the 1.75/cell refer to exactly?

Does the controller have settings for temperature compensation or does that have to be figured and then input?
How is the temperature compensation figured?
Can the tristar be programmed with a  modern laptop computer that has no serial port? It has HDMI and USB3.0 ports.

Marc Kurth

Lumisol said:

I will be using a tristar mppt 30  controller to charge my 6 volt agm batteries (48 volt bank).
The battery specs for charging say:

25A @ 1.75/Cell	500Min
75A @ 1.75/Cell	125Min

Those specs are referring to storage capacity. Not charging. 

They are saying that the battery will sustain a load of 25A for 500 minutes, before the voltage falls to 1.75v per cell.
Minutes at 25 amps is also known as "RC" or Reserve Capacity.

Same concept applies at a 75 amp load, but it will reach the low voltage of 1.75v per cell in 125 minutes.

Aside from the marketing machine being applied, Vmax are just re-branded generic AGM's from Ritar.  The Absorb and Float voltages will be similar to Deka, UPG, etc.- but stay on the mid to low side with Vmaxtanks.  Do not exceed a charge rate of 20A to 25A per 100A of battery bank capacity - this is critical with that particular battery design.

I believe that you will end up with 58v for Absorb and 54v for Float at 77F.

Marc

Marc Kurth

But do your homework to be sure that you follow their specs!

Marc

Lumisol

So for a 225 ah bank at 48 volts, you say 40 to 50 amps of charge? Does the tristar even put that much out?

Today's low was 36 and the high was 55... what would the charge voltage be?
I know the batteries are very good I didn't know they were Ritar. Nice.
I found that Vmax USA manufactures their batteries, they also make the Ritar batteries?
Does the controller have settings for temperature compensation or does that have to be figured and then input?
How is the temperature compensation figured?
Can the tristar be programmed with a  modern laptop computer that has no serial port? It has HDMI and USB3.0 ports.

mcgivor

What @Marc Kurth said was "Do not exceed a charge rate of 20A to 25A per 100A of battery bank capacity - this is critical with that particular battery design.

Your battery is 48v 225Ah so the maximum would be as you stated, but the word maximum doesn't mean you have to change at maximum, the TriStar 30 has a maximum rating of 30 amps and should be sufficient, around 10% of the battery capacity is ideal, so 22.5 amps. Having said that the sun rises slowly, so the current and voltage increases slowly, until it  completes the bulk stage of charging, (the absorption voltage setting) then the current will begin to taper down during the absorption cycle, depending on how deeply discharged the battery was, will determine how much current is needed, this is why you did the load calculation, to size the battery and the system to maintain the charging requirements. On a shallow depth of discharge you may never approach the controllers maximum capacity, or even the 22.5 amps , but should you miss a days charge due to weather, or discharge a little deeper for whatever reason, the extra capacity will be available to compensate and have a little more charge capacity.

If you choose a setting for AGM using the dip switches the temperature compensation will be the default and no adjustments are required, the voltage  will increase 0.60 V for every 9°F below 77°F for a 48v battery and decrease voltage 0.60 V for every 9° F avove automatically, My suggestion is to choose a default algorithm that is close to the manufacturer's figures and see how things work before changing setpoints without fully understanding how you system is working, this takes time.

Apparently you can plug in a router and use wifi but I've not done that so, no additional coment.

Marc Kurth

Lumisol said:

So for a 225 ah bank at 48 volts, you say 40 to 50 amps of charge? Does the tristar even put that much out?

Today's low was 36 and the high was 55... what would the charge voltage be?
I know the batteries are very good I didn't know they were Ritar. Nice.
I found that Vmax USA manufactures their batteries, they also make the Ritar batteries?
Does the controller have settings for temperature compensation or does that have to be figured and then input?
How is the temperature compensation figured?
Can the tristar be programmed with a  modern laptop computer that has no serial port? It has HDMI and USB3.0 ports.

Ritar is a large manufacturer in China making many batteries carrying different labels. Vmax does not have their own manufacturing plant, they are a sales and marketing machine.

Their technical specs are like Deka and Universal Power Group, and they are in the price range of Concorde and Fullriver. They have a 1 year warranty so treat them carefully and they should work fine for a few years in a seasonal, shallow cycle application.

Marc

jonr

From the specs (volts are per 6V, amps don't change for series connections):

Float volts: 6.69V-6.81V
Charging volts: 6.9-7.05V
Charging amps: 15A-55A

The voltage values are lower than the TriStar defaults for AGM, but you can use a custom setting.  They also seem low, so I'd use the high end (perhaps 6.80V float and 7.05V charge) and check idle voltages (across each individual battery).  Others know better on this issue.

Lumisol

Marc Kurth said:

Lumisol said:

So for a 225 ah bank at 48 volts, you say 40 to 50 amps of charge? Does the tristar even put that much out?

Today's low was 36 and the high was 55... what would the charge voltage be?
I know the batteries are very good I didn't know they were Ritar. Nice.
I found that Vmax USA manufactures their batteries, they also make the Ritar batteries?
Does the controller have settings for temperature compensation or does that have to be figured and then input?
How is the temperature compensation figured?
Can the tristar be programmed with a  modern laptop computer that has no serial port? It has HDMI and USB3.0 ports.

Ritar is a large manufacturer in China making many batteries carrying different labels. Vmax does not have their own manufacturing plant, they are a sales and marketing machine.

Their technical specs are like Deka and Universal Power Group, and they are in the price range of Concorde and Fullriver. They have a 1 year warranty so treat them carefully and they should work fine for a few years in a seasonal, shallow cycle application.

Marc

If they last a year it would be great. That's enough to get my money's worth out of them. If they happen to last longer than that it will be gravy.
I looked at the Ritar plant and it is indeed an impressive facility.
Where do you see a list of battery brands made by Ritar? Could you provide a link as I am interested in this aspect of the process.
Thanks.

Marc Kurth

It's common knowledge in the battery industry. Vmax doesn't want to talk about it because they want a unique brand identity, It is similar to the OEM deals where Fullriver sells batteries to other companies, who put their own label on them. Right now, I could have AGM or Lithium batteries with my own private label on them. The factories don't care - they want to move product.

You should set your goals higher regarding battery life.

Lumisol

So you are going off of hear say for your sources on the manufacture of batteries? That's a risky proposition. Believe half of what you see and none of what you hear is a solid philosophy, and always make people prove their claims, if they can't, I don't believe them.
If the batteries last a year, I'll be switching to Tesla powerwall with a 10 year warranty and a way better profile and stats.

Marc Kurth

That post spoke volumes about you. Best of luck to you.

Lumisol

Thanks.
I love my S sedan and I am sure the build quality will be extremely high for the batteries as well.
I wonder if it will have a "ludicrous Power" button on it like the car does. (Ludicrous Speed)

BTW, I got the car for free basically so it's a good thing for that reason too.

Estragon

With AGM batteries I'd be inclined to just turn everything off and disconnect batteries for the winter. They should have a low self-discharge rate. Just make sure they're fully charged as they can be damaged by freezing and sulfation if left only partially charged.

The charge controller will use some power just being on, and if panels get snow covered that power can discharge the bank and cause the problem leaving the controller on is supposed to prevent. I found that out the hard way.

westbranch

Alternatively, just get a PWM CC and hook up two panels ( assuming GT ~30V panels) to 'trickle charge' it for the winter

Lumisol

My panels are 44 volts. I like the idea of just shutting it all down for the off season. Maybe I could get a caretaker to move in for the off season like in The Shining...nah.

Estragon

@westbranch - I have flooded L16 batteries which may self-discharge too much over the winter, so plan to do exactly that. A couple pairs of panels (2x 150w 12v + 2x 300w ~70vmpp) mounted vertically to a pair of pwm controllers to float over the winter. Flooded batteries on the boat seem to survive the winter okay on their own, so maybe I'm overthinking it?

@Lumisol - if mine were AGMs I would just leave them disconnected over the winter. If you do end up getting lithium, they apparently don't like charging cold.

Lumisol

Powerwall has a fairly wide operating range. [quote] Operating Temperature-4° to 122°F / -20°C to 50°C [/quote]

Estragon

My understanding is that lithium shouldn't be charged at <0C. Discharge is okay colder, but powerwall heats the battery to charge if <0C. What happens if heater fails, I don't know.

Lumisol

You get your money back. It has a 10 year warranty.

Estragon

It probably records record high/low temp like charge contrllers record high voltage. -20C can be highs for weeks in winter here, so the cynic in me sees the warranty as questionable.

I also don't know what happens if you charge a lithium battery at -30c. Does it just not charge, or hurt the battery, or?

Raj174

Cold temperatures increase resistance in LFP cells. The increased resistance causes the production of heat and subsequent breakdown of the electrolyte which causes plating to occur. This is more prevalent when charging and non recoverable, not so much with discharging. IMO LFP should be used in controlled environments. Mine are in an air conditioned space.

Rick

Estragon

Could the heating get to dangerous levels in "normal" cold conditions (eg -40), or would the heating make the process somewhat self-limiting (as cells warm, resistance drops)?

Raj174

I think the published charge/discharge temps from manufacturers are solid limits since the have to warranty their product. I read of some EV guys trying  to slowly heat up LFP cells using low current at freezing temps and it appeared to work but I think that some plating does occur which decreases both the life and the capacity of the cells. Best not to go near the limits. To me a conservative range would be 35 to 90 degrees F for recommended charging rates.   

Marc Kurth

Raj174 said:

Cold temperatures increase resistance in LFP cells. The increased resistance causes the production of heat and subsequent breakdown of the electrolyte which causes plating to occur. This is more prevalent when charging and non recoverable, not so much with discharging. IMO LFP should be used in controlled environments. Mine are in an air conditioned space.

Rick

Rick,

My initial thought is that with a constant incoming voltage, wouldn't the current draw reduce as battery resistance increased?  Seems like that in turn, would reduce the charge rate which would reduce heating. I could see increased heating with a constant wattage load, but not with batteries.

The opposite is an ever increasing battery temperature with ever decreasing resistance, causing the current draw to increase, generating more heat. Hence, thermal runaway cautions with hot batteries.

It is clearly not my intent to correct you - I am trying to understand what I am missing!

Marc

Raj174

Hi Marc,
I think it has to do with the various types of chemicals in the electrolyte. Check out a couple of paragraphs from an article on this subject and see what you make of it. 

From this article titled "Nonaqueous Liquid Electrolytes for Lithium-Based Rechargeable Batteries" by Kang Xu from the Electrochemistry Branch, Sensor and Electron Devices Directorate, U.S. Army Research Laboratory, Adelphi, Maryland 20783-1197 published in the Chem. Rev. 2004, 104, pp4303-4417.

"Thus, at temperatures lower than the liquidus temperature (usually above -20 °C for most electrolyte compositions),50e,159,160 EC precipitates and drastically reduces the conductivity of lithium ions both in the bulk electrolyte and through the interfacial films in the system. During discharge, this increase of cell impedance at low temperature leads to lower capacity utilization, which is normally recoverable when the temperature rises. However, permanent damage occurs if the cell is being charged at low temperatures because lithium deposition occurs, caused by the high interfacial impedance, and results in irreversible loss of lithium ions. An even worse possibility is the safety hazard if the lithium deposition continues to accumulate on the carbonaceous surface.

"At temperatures higher than 60 °C, various decompositions occur among the electrolyte components, electrode materials, and SEI or surface layers, while LiPF6 acts as a major initiator or catalyst for most of these reactions.152,310,332,333 The damage caused by high-temperature operation is permanent. Because gaseous products accumulate, a safety hazard is also likely. Therefore, the specified temperature range for the normal operation of most commercial lithium ion cells is -20 °C to +50 °C. While sufficient for most consumer purposes, the above range severely restricts the applications of lithium ion technology for special areas such as military, space, and vehicle traction uses."

Here is the author's bio, "Kang Xu was born in Chengdu, China, and received his B.S. degree in Chemistry from Southwest Normal University in Chongqing, China, in 1985 and M.S. in Polymer Chemistry from Lanzhou Institute of Chemical Physics, Academy of Sciences, in 1988. After working on polymer electrolyte materials from 1988 to 1992 at Chengdu Institute of Organic Chemistry, Academy of Sciences, he went to Arizona State University and received a Ph.D. degree in Chemistry in 1996 under the tutelage of C. Austen Angell. From 1997 to 2002, he was awarded the National Research Council Research Associate Fellowship and the American Society for Engineer Education Postdoctoral Fellowship, respectively, and he served during the tenures as a guest researcher at U.S. Army Research Laboratory with T. Richard Jow as academic advisor. He was employed by the U.S. Army Research Laboratory in 2002. His research interests concern materials development for electrochemical energy storage applications, which include lithium or lithium ion batteries and electrochemical capacitors. He won R&D Achievement Awards from the Department of the Army in 1999, 2001, and 2002 for his work on electrolyte materials. He authored over 60 research publications and 11 patents and is a member of the Electrochemical Society."

Marc Kurth

I do see that low temperature charging will cause damage. But I note see that the article is from 2004 discussing the LiPF6 formulation. Lots for me to learn still!

Thank you.

jonr

Winston LYP batteries claim to charge at -45C to 85C.

Raj174

Yep, but I have yet to hear anyone who has them verify that.