diy solar

diy solar

Looking at Crown sealed lead acid. Any input?

R

Roswell Bob

Solar Enthusiast
Joined
Dec 5, 2020
Messages
759
Location
Warner, NH
I ordered 16 of the Lishen LIFePO4 272/280 Ah cells to replace my Sears Die Hard units that I have 5 years on. Seems there is some kind of cluster-F**K going on behind the scene delaying shipments. If I don't get good news on LiFePO4 units I will go another round with the lead acid units.

I was interested in the Trojan T105 units, but thought the Crown AGM 6CRV220 might be a better choice.

I keep them in my basement so no gassing and no maintenence are very appealing. I have a bunker in my basement with 12" thick walls and a 300 pound steel door. Temperature wanders from 65F to 75F so good there.

I use about 6kWh/day, and that is mostly when sun is shining so cycles will not be very deep.

Am I on right track with the Crown AGM? Must I limit charging current to 13% of 20 hour rate?

Thank you.
 
If those cells are coming from China I would expect 70 to 90 days. The SNAFU has been on for at least a year now. No end in sight for 2021.
I would try to wait for the LFP rather than going AGM.

I can't speak for Crown but my experience is AGM prefers to charge fast and hard. I would only limit the voltage not the amps.
 
I've found that the Crown CR-220 seems to be a good amount of KWH for the money. I've got a small test setup in my camper (4 of them), and can go 4 days off grid without solar, with an energy hungry electric fridge. I could go longer, but the fridge cuts out at 11.7 volts. They have taken a fair amount of abuse( sub freezing conditions, 100% discharge when I forgot to disconnect them when I dropped it off for service), and seem to be holding up well.

Obviously that isn't a good fit if you don't want off gassing, but just throw them in a cabinet and vent it. Over all I've been impressed.

If you find a local golf cart shop you should be able to pick them up for 100-125 each, which is decent per kwh.
 
Thanks for comments. I thought the sealed units didn't outgas. Batteries and inverter would be together in a 6'x12' concrete bunker with little/no ventilation. I would be concerned that the acrid atmosphere created by a gassing call array might not play well with the inverter. PCBs tend to like plenty of clean fresh air.

Prices I have seen are about $270 sans shipping for the AGM 6CRV220. Are we talking the same units? I don't think so at your 100-125 each.

thanks
Bob
 
AGM SLA does not gas unless there is a problem with the battery or there is an overcharge situation. Probably never happen but it can and you will probably be aware of the situation soon.
 
Correct, I'm using the CR-220, which is a traditional lead acid. It's significantly cheaper, but you need to vent it, and check the fluid in the cells every couple months.

The benefit is simply the price due to the production volume.
 
time2roll said:
AGM SLA does not gas unless there is a problem with the battery or there is an overcharge situation. Probably never happen but it can and you will probably be aware of the situation soon.
Click to expand...
Do these AGM ever need desulphate mode? I would be a little concerned with 'baking' these sealed units.
 
AGM's are sealed (with pressure relief vent). AGM's are also electrolyte starved design meaning they only have a limited amount of electrolyte soaked in glass mat.

You do not want to overcharge them as this excessively splits water in electrolyte to oxygen and hydrogen gas. For normal charging there is a small amount of gassing that is confined and reabsorbed but if too great due to overcharging the pressure relief port will vent and you lose non-replaceable water from electrolyte.

Do not run a 15v+ equalize charge cycle on a 12v AGM battery. It will cause them to vent gas.

AGM have pure lead plates vs normal flooded lead acid that have an alloyed support grid embedded in plates. AGM's are structually held together by pressuring the soft, flimsy, pure lead plates between the glass mat layers. Because they are pure lead plates and their electrolyte is typically mixed at a slightly higher acid concentration, their float and absorb voltage is typically a few tenths of a volt higher then regular flooded lead acid batteries. They have lower self discharge rate.

Because of being packed together with glass mat their electrolyte ion migration path distance is less then regular flooded lead acid batteries. This gives them their main advantage of lower impedance which gives them greater peak current capability and faster recharge rate. This gives them better round trip discharge-charge energy efficiency compared to regular flooded lead acid.

At 0.15 CA charge and discharge rate:

Regular flooded lead acid round trip -> 80% efficient
AGM -> 90%
LFP -> 99%

AGM's are more delicate and less forgiving of abuse that a flooded lead acid can take.
 
Last edited:
RCinFLA said:
AGM's are sealed (with pressure relief vent). AGM's are also electrolyte starved design meaning they only have a limited amount of electrolyte soaked in glass mat.

You do not want to overcharge them as this excessively splits water in electrolyte to oxygen and hydrogen gas. For normal charging there is a small amount of gassing that is confined and reabsorbed but if too great due to overcharging the pressure relief port will vent and you lose non-replaceable water from electrolyte.

Do not run a 15v+ equalize charge cycle on a 12v AGM battery. It will cause them to vent gas.

AGM have pure lead plates vs normal flooded lead acid that have an alloyed support grid embedded in plates. AGM's are structually held together by pressuring the soft, flimsy, pure lead plates between the glass mat layers. Because they are pure lead plates and their electrolyte is typically mixed at a slightly higher acid concentration, their float and absorb voltage is typically a few tenths of a volt higher then regular flooded lead acid batteries. They have lower self discharge rate.

Because of being packed together with glass mat their electrolyte ion migration path distance is less then regular flooded lead acid batteries. This gives them their main advantage of lower impedance which gives them greater peak current capability and faster recharge rate. This gives them better round trip discharge-charge energy efficiency compared to regular flooded lead acid.

At 0.15 CA charge and discharge rate:

Regular flooded lead acid round trip -> 80% efficient
AGM -> 90%
LFP -> 99%

AGM's are more delicate and less forgiving of abuse that a flooded lead acid can take.
Click to expand...
Thank you. You've made up my mind with that last sentence. I don't deal well with delicate and less forgiving. I'm hard on women, shoes and batteries. I'll continue with plan to switch to the LiFePO4.
 
RCinFLA is mostly right but be Careful - MOST agm's are made out of recycled-lead like all the rest. You have to identify, specify, and pay more for pure-lead agm's like Enersys and some other makes.

Commonly found agm's made out of recycled-lead are known as "conventional agm's". Pure-lead is different for the reasons he gave above.

Conventional agm's are restricted to about no more than 0.25c inrush current to charge properly, whereas *with care* about your CV voltage, pure-leads can handle 0.5 to 1C. This was my gateway chemistry to LFP. :)

The proviso is that since pure-lead agm's can easily be found in the consumer market, there is a temptation to use somebody else's (prior owner) trash, and not achieve the results hoped for. Ie, buy from a reputable source as an original owner.

This is where the reputation of agm's being "delicate" come from. Those that don't buy from reputable sources, or those that apply shade-tree slap-together engineering along with arc-welders as charge sources.
 
Roswell Bob said:
Do these AGM ever need desulphate mode? I would be a little concerned with 'baking' these sealed units.
Click to expand...
My only knowledge on this relates to what Lifeline brand says to equalize/desulphate only if there seems to be a premature loss of capacity. Also time to review your charging systems if this seems necessary. Undercharging is frequently a worse problem than overcharging.
 
You must log in or register to reply here.
Back
Top