Charging SLA at 0.35C?

[Goombah111]

Can I charge a 20ah SLA at 7a?

 

[snoobler]

Depends

 

[Goombah111]

Depends

Gonna take that as a yes. YOLO

 

[snoobler]

Brave.

 

[time2roll]

afaik SLA can mean a few different things

 

[Substrate]

Exactly - kind of a trick question, but I'm going to assume a conventional agm.

They are not designed to be charged faster than about 0.2 to 0.25C. Depending on age, quality etc you can, but you'd be stressing the very thin plates. In addition, there is no benefit due to efficiency. In other words, you can charge them fast in bulk (provided you aren't damaging the plates), but you will pay for it on the back end with a longer absorb period.

So nothing truly gained. If you do a capacity test, you'll see why there is no benefit.

As for the tricky part mentioned about an sla or "sealed lead acid" there are 3 major types:

1) MF (maintenance free) flooded lead acid. To emulate 4 years of owner neglect, these were developed primarily for the automotive industry where extra electrolyte was added to the cells, and then permanently capped off. Sealed.

2) Gel. Instead of electrolyte sloshing around the plates, the electrolyte is a viscous liquid, much like jello. Sealed up.

3) AGM. Instead of sloshing elecrolyte, the plates are pressed together with a very thin matt as a separator, in which the electrolyte is absorbed into the matt and sealed.

4) Pure-Lead AGM. These are made of highly pure (99% typical) lead, and are capable of 0.5 to even 1C charge rates, but that should not be taken lightly or casually. Also sealed.

Common forms of abuse with gel and agm: users pop open the caps, and upon not seeing sloshing liquids, they pour water into it. Unfortunately, they have now changed their SLA, into a poorly-performing flooded lead acid battery, but continue to charge and treat it like an agm! Overflowing acidic electrolyte pours all over your desk and pants.

Older forms of abuse consisted of the ever popular plate-eating epsom-salts, and if your grandparents are still around, putting an aspirin in each cell. Not recommended.

 

[Goombah111]

afaik SLA can mean a few different things

I think it can mean gel, flooded, and AGM. Mine is AGM I think, it doesnt say. Heres the box. I managed to get 4 of these for 40$ so I'm using it with 1 panel as a secondary 24v side-system.

 

[Goombah111]

you will pay for it on the back end with a longer absorb period.

Okay I'll let these batteries become test subjects to this fast-charging until I take the plunge on these LiFePo4's.

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[time2roll]

"MAX 3.0 A" looks pretty clear to me. At least try to stay at the low end on voltage (14.5) if pressing the amps.

 

[Goombah111]

"MAX 3.0 A" looks pretty clear to me. At least try to stay at the low end on voltage (14.5) if pressing the amps.

Im just gonna let my MPPT do it's thing and hope it doesn't explode. In full sun its gonna be 7a 24v with 2 sets of 2 batteries in parallel so will be exceeding the "initial current" rating by 1a.

 

[snoobler]

Im just gonna let my MPPT do it's thing and hope it doesn't explode.

If you care about preserving it, set bulk/boost/absorption/float to 13.8V. At the lower voltages they can often take more than rated, but it will take a longer time to eventually fill. You might not get to true 100% charge in a solar day.

 

[Goombah111]

If you care about preserving it, set bulk/boost/absorption/float to 13.8V. At the lower voltages they can often take more than rated, but it will take a longer time to eventually fill. You might not get to true 100% charge in a solar day.

I will keep that in mind, thanks for the tip.

 

[Substrate]

Yes, those are agm. Ok, looks they snuck the spec up to 0.3C ok.

But you didn't mention more than one. So the same rules apply about balance. I would have personally charged each one up individually before assembling into a bank, but you'll find out soon enough if one blows it's top!

Fortunately, this appears to be a fun learning experience kind of thing, so cool - still, keep your ears open for rice-crispies that first time out, and don't put your face close to the bank if you are taking measurements or trying to listen for the crispies.

 

[Goombah111]

you didn't mention more than one

"I managed to get 4 of these for 40$ so I'm using it with 1 panel as a secondary 24v side-system."

I would have personally charged each one up individually before assembling into a bank

They all had the same voltage so i went with it. Heard bottom balancing is better.

keep your ears open for rice-crispies that first time out,

Ive had em out there for only 4 days now, will continue to keep a close eye on them. Im obsessed with checking everything constantly when I get a new system, i get a weird enjoyment out of it. These are like my toys and I love playing with them.

appears to be a fun learning experience kind of thing,

Definitely. Trying to learn and upgrade as I go slowly incorporating more expensive and dangerous setups when I feel comfortable. One day i hope this hobby turns into a practical financial endeavor.

Thanks for the help.

 

[snoobler]

"I managed to get 4 of these for 40$ so I'm using it with 1 panel as a secondary 24v side-system."


They all had the same voltage so i went with it. Heard bottom balancing is better.

You heard horrifyingly wrong. There's never a reason you actually want to take a lead-acid battery to empty. Ever.

When you hit peak voltage, you need to check the 12V in each string. You may find they are way out of whack. I second @Substrate 's recommendation to top charge all 4 individually or at least in parallel to peak voltage.

 

[Goombah111]

You heard horrifyingly wrong. There's never a reason you actually want to take a lead-acid battery to empty. Ever.

Never said empty. Heard bottom balancing, especially LiFePo, is better but that doesnt mean empty, it means 3.2v per cell. In this case it'd be 2v per cell as SLA shouldnt be drained past 50%.

I second @Substrate 's recommendation to top charge all 4 individually or at least in parallel to peak voltage.

Im constantly checking the voltages etc, will make sure it's good don't worry thanks for the concern.

 

[Substrate]

Whew - it's just that sometimes in this text-based world, we don't know the whole context of the situation.

Because there ARE some people out there who have been told by salesman that one should totally drain their lead-acid batteries before charging - which is wrong.

Anyway, you spent only $40 on the batts, but do yourself a favor and grab one of the small $20 2A "trickle chargers" and charge each one up. Then go to town.

 

[Goombah111]

Anyway, you spent only $40 on the batts, but do yourself a favor and grab one of the small $20 2A "trickle chargers" and charge each one up. Then go to town.

I got one of those iMax B6 chargers, I may do that at some point.

 

[Substrate]

Well there you go!

Just in case - like A123 and Headways cells, there are a lot of counterfeit iMax chargers. If so, you may be able to calibrate it:

Of course, your reference voltmeter should be good.

 

[Goombah111]

there are a lot of counterfeit iMax chargers. If so, you may be able to calibrate it:

Mine is undoubtedly one of the fake ones but has served me well over the years. It is a little off on the voltage though, I'll give calibrating it a try.