Battery Charging

kelperis · October 2018

I read somewhere that people use the ‘engine starting’ feature of their automotive battery charger, to charge their battery bank faster (more amps) than regular charging. Is this something that should be done? My batteries are 12v 200ah 30amp gel Renogy brand. Also, someone said I don’t need to worry about the amp limit on the battery bank, because it is per battery, so in my case, I can charge them at 180amps safely, using multiple charge controllers or combined with a bulk charger. Is this something that others do?

mike95490 · October 2018

Gel batteries are only suited for Float Charging, not for solar use. High rate charging destroys them very quickly.

If you have AGM batteries, and are calling them gel, you are wrong. AGM batteries can be charged at higher rates.

Most chargers with a "boost" feature, generally limit that mode to 90 seconds or so, because the charger will overheat

excerpt: https://www.batterystuff.com/kb/articles/battery-articles/gel-vs-agm.html
AGM (absorbed glass mat) is a special design glass mat designed to wick the battery electrolyte between the battery plates. AGM batteries contain only enough liquid to keep the mat wet with the electrolyte and if the battery is broken no free liquid is available to leak out.

Gel Cell batteries contain a silica type gel that the battery electrolyte is suspended in, this thick paste like material allows electrons to flow between plates but will not leak from the battery if the case is broken.

kelperis · October 2018

I must have confused you. The following link references the batteries I have. They are marketed by their vendor for solar power systems. They are included in kits by their vendor, for home solar power systems. Are you saying they won’t work at all for this purpose, or are you saying they perform poorly?
https://www.renogy.com/renogy-deep-cycle-pure-gel-battery-12-volt-200ah/

bill von novak · October 2018

kelperis said:

I must have confused you. The following link references the batteries I have. They are marketed by their vendor for solar power systems. They are included in kits by their vendor, for home solar power systems. Are you saying they won’t work at all for this purpose, or are you saying they perform poorly?

They're just not a great choice. At a 50% DOD those batteries will last less than three years. So they _can_ work as long as you budget for replacements every three years. (Gel batteries are best for UPS applications, where they can last a long time.)

kelperis · October 2018

Hmmm, I sure hope your wrong. They are marketed to last 10 years.

To the question: using the starting function of the charger seemed off to me, because my experience with auto battery chargers work just as you say. My charger is 35am charging with standard types of charging. But what about the multiple charging sources, ie charge controllers and or charging inverters, etc?

cow_rancher · October 2018

kelperis said:

Hmmm, I sure hope your wrong. They are marketed to last 10 years.

The key word here is "marketed".

Rancher

littleharbor2 · October 2018

The specs I see on their data sheet say 3 year warranty. Also 1000 cycles @ 50% DOD. That's 3 years as well although Daily 50% DOD is not a well designed battery bank. That would leave zero days of autonomy

mike95490 · October 2018

kelperis said: ....My batteries are 12v 200ah 30amp gel Renogy brand..

No confusion on my part, GEL seems to be pretty plainly spelled out in the model # you quoted. Peddlers and marketing weenies are to blame for using the wrong terms, and the more folks they can confuse with double speak, the more profit in their pocket

mcgivor · October 2018

Is the Gel versus AGM discussion a matter of lumping all designs into one category, much like Lithium chemistries are all perceived as dangerous? Rationale behind this is some manufacturers actually claim certain Gel batteries, tubular type to be specific, are better than AGM in cyclical applications within their own formats. One must read between the lines (or lies?) specifically with regards to discharge currents, where Gel is unable to compete with AGM, it's important to recognize that the Gel are unable to recharge at the same voltages, which influence currents, as AGM . Please note I'm not provoking an argument in any way shape or form, just reading from the attached Pdf

mike95490 · October 2018

The major difference is that Gel, has immobilized electrolyte, as in jelly. Because there can be no "flow or circulation", recharge rate is quite limited, and too fast of recharge (4 hours of solar) causes irreversible bubbles in the gel/plate interface that never go away.
A week of heavy use & recharge, can destroy a Gel bank. Mostly only good for FLOAT service, like in a UPS or EXIT sign light,

AGM, the fluid is able to move about, bubbles get re-combined at the catalyst caps, and the battery can be quickly recharged, like in a short solar day.

But go ahead and believe the sales droid, it's his job to separate you from as much $ as possible, as often as possible.

mcgivor · October 2018

Totally agree with the above statement, the deep cycle performance of Gel may be better than AGM under controled laboratory conditions, where slow discharge and grid supported charging is available. This would allow long slow charging rates which are impractical in an offgrid application, so one must read between the lies, if there is no mention of offgrid applications in the Datasheet there is probably a good reason.

Marc Kurth · October 2018

It's all about system design. Rules of thumb are just that, and nothing more. I have been at this for a lot of years, and I keep discovering that what I "knew to be true" is true sometimes, but not others.

Gel can provide a very long life if cycled very, very shallowly. I have several off grid systems pushing 14 years old with Gels that are still running. YES, it takes a big investment upfront to buy enough battery, lots of PV - AND setting it up to avoid deep cycles. I think that we all know of many applications that have phenomenal battery life - because of the application.

PV is still comparatively cheap, Enough battery and PV capacity on a cyclic system. begins to approach a standby system.

The analysis of the payback crossover needs to include the future inflated cost of batteries, vs. invested cost today.

Am I making a case for Gel vs. AGM vs. Flooded vs. Lithium? Oh, heck no.

Just trying to remind everyone of the basics.

Some folks always gravitate toward lowest first cost. Others look further out with an eye to long term cost of ownership.

Respectfully,

Marc

kelperis · October 2018

I appreciate everyone’s comments. The strategy behind my approach, is to provide UPS/Battery BKUP functionality, which we need for medical reasons (that my utility can’t provide), as well as use solar to cover as much load as possible. I would have to spend more than half of what I have for that function alone. By combining the requirements, the investment pays for itself pretty quickly. The money invested earns maybe 3-5%, but by providing a portion of my living expenses, I can easily double that return. Economics aside though, if I have to add more charging capacity in order to cover the load, I need to determine that early in testing as soon as the system is all connected up. There is value in using a vendor that provides turnkey systems, as they are increasing their liability with the bundled product. That being said, as many of you caution, ‘let the buyer beware.’

Battery Charging

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