DC Chargers?

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rancherlee
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Re: DC Chargers?

#16 Post by rancherlee » Sat Aug 11, 2018 1:29 pm

Also be mindful, due to the way they are built, deep cycle batteries won’t take more than a 10amp charge while being charged with a 14.4v alternator source. Trying to charge them faster with a higher voltage source really shortens the life cycle. Just some testing with the 30 amp mode on my big garage charger only shows ~15amp charge while charger is pushing 15.5v+ at that setting on a fairly new battery that was depleted to 25%. It would take a good 6+ hours of running the outboard recharge a rundown deep cycle.
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Marc K
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Re: DC Chargers?

#17 Post by Marc K » Sat Aug 11, 2018 6:29 pm

rancherlee wrote:
Sat Aug 11, 2018 1:29 pm
Also be mindful, due to the way they are built, deep cycle batteries won’t take more than a 10amp charge while being charged with a 14.4v alternator source. Trying to charge them faster with a higher voltage source really shortens the life cycle. Just some testing with the 30 amp mode on my big garage charger only shows ~15amp charge while charger is pushing 15.5v+ at that setting on a fairly new battery that was depleted to 25%. It would take a good 6+ hours of running the outboard recharge a rundown deep cycle.
I will respectfully disagree because there are true deep cycle batteries that will be damaged by such slow charging. A good rule of thumb for many Walmart grade "marine" wet cell batteries is to charge them at around 13% of their C/20 nameplate rating. So, a basic 100 ah Group 27 might like being charged at about 13 amps.

But that number is around half of the minimum charge rate specified for some true deep cycle batteries. Charging them slowly will dramatically shorten their life.

Remember that battery impedance changes with state of charge, so the current draw reduces as the battery fills up. So, yes - bumping the voltage to 15+v will push more amps at a given impedance, but it also boils the electrolyte. The acceptance rate will vary with type, style, age and manufacturer. There is no single best number.

For example a high quality 100 ah AGM will happily accept a 200 amp charge rate at 14.4v when depleted. Then, when it reaches full charge, it will only accept 1/2 of an amp at 14.4v.

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Henpecked
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Re: DC Chargers?

#18 Post by Henpecked » Sat Aug 11, 2018 9:02 pm

I work on UPS systems for a living. We use banks of deep cycle batteries. A depleted battery will charge as quickly or slowly as you want. I've seen 100A or more pumped into a battery string during a recharge after a power outage, but that's not typical. Most of the equipment I work on uses current limiting to keep the charge between 10-15A. As the bus nears float voltage level, the current tapers off to 0A. I can't tell you how a boat motor charges a battery. I'm still a newb looking for my first used boat/project.

A solar panel can cut into your discharge depth and keep your batteries topped off when the boat is in storage.

boocat
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Re: DC Chargers?

#19 Post by boocat » Sun Aug 12, 2018 5:28 am

Marc K wrote:
Sat Aug 11, 2018 6:29 pm
rancherlee wrote:
Sat Aug 11, 2018 1:29 pm
Also be mindful, due to the way they are built, deep cycle batteries won’t take more than a 10amp charge while being charged with a 14.4v alternator source. Trying to charge them faster with a higher voltage source really shortens the life cycle. Just some testing with the 30 amp mode on my big garage charger only shows ~15amp charge while charger is pushing 15.5v+ at that setting on a fairly new battery that was depleted to 25%. It would take a good 6+ hours of running the outboard recharge a rundown deep cycle.
I will respectfully disagree because there are true deep cycle batteries that will be damaged by such slow charging. A good rule of thumb for many Walmart grade "marine" wet cell batteries is to charge them at around 13% of their C/20 nameplate rating. So, a basic 100 ah Group 27 might like being charged at about 13 amps.

But that number is around half of the minimum charge rate specified for some true deep cycle batteries. Charging them slowly will dramatically shorten their life.

Remember that battery impedance changes with state of charge, so the current draw reduces as the battery fills up. So, yes - bumping the voltage to 15+v will push more amps at a given impedance, but it also boils the electrolyte. The acceptance rate will vary with type, style, age and manufacturer. There is no single best number.

For example a high quality 100 ah AGM will happily accept a 200 amp charge rate at 14.4v when depleted. Then, when it reaches full charge, it will only accept 1/2 of an amp at 14.4v.

Marc
Hmm, so all those 3 bank 20 amp name brand chargers out there will kill batteries in what ,,6 months? a year, I'm just wondering.

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Re: DC Chargers?

#20 Post by Marc K » Sun Aug 12, 2018 7:43 am

Heck no - not sure how you got that from my post. I certainly did not mean that! Let me put it differently.

With a typical 100 ah battery used with 12v and 24v trolling, a 20 amp charge rate is 20% of the battery capacity - right on target - per my previous comments. In other words, your example is not slow charging because it is nicely above the 13% charge rate for Marine batteries, and that's healthy.

The result in lifespan reduction that I was referring to would be dependent on the average depth discharge. If you are draining the battery to 10% to 20% remaining capacity, the effect is amplified. If you are only using the top 20% to 30% of the battery capacity, the impact of slow charging is almost nil. But then, that is not a deep cycle application.

Yes, using a 20 amp charge rate on a 200 ah deeply cycled true deep cycle AGM battery will shorten the lifespan, because they are specifically designed to charge quickly when deeply cycled. The impact of slow charging will depend upon how deep the discharge was. Many deep cycle applications regularly discharge down by 80% to 90% depth of discharge. That's when it makes the most difference. Remember that true deep cycle batteries are rated to discharge down to 20% remaining, around 500 times. Kill a battery is six months or a year? Certainly not. But it can reduce a 9 year lifespan to 4 years, and true deep cycle batteries are not cheap. Remember that we are also discussing two types of batteries: True deep cycle and Marine batteries. They are different.

My comment was to explain why 10 amps is not a maximum charge rate for all deep cycle batteries

Marc
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boocat
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Re: DC Chargers?

#21 Post by boocat » Sun Aug 12, 2018 8:05 am

From what I understand, a 3 bank 20 amp is 6.6 amp per bank or about that. I could be wrong

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Re: DC Chargers?

#22 Post by boocat » Sun Aug 12, 2018 8:10 am

I"m talking plain old flooded lead acid deep cycle marine, like an interstate srm27 or equivalent. But anyway, I think we are getting a little off from the o.p. My apologies, but do love the conversation. I'm currently in the middle of an install.

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Re: DC Chargers?

#23 Post by rancherlee » Sun Aug 12, 2018 12:53 pm

I thought we were referring to “marine” deep cycle also, hence my comments on them not taking a high rate of charge. To most of the people on this forum a “deep cycle” is an average lead acid battery you use for a trolling motor or camper. I’ve worked with HD deep cycles on forklifts and heavy equipment. Those will take a pretty fast charge but they are not cheap.
1988' Kennedy 20' "Haley's Comet"
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Marc K
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Re: DC Chargers?

#24 Post by Marc K » Sun Aug 12, 2018 1:15 pm

Sorry, I thought that I was being clear in addressing both types of lead acid batteries- AGM and flooded.
Certainly didn't mean to confuse people, that was not my intent.

Again, my whole point was that deep cycle batteries typically used in trolling applications are not limited to a 10 amp charge rate because of their design
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boocat
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Re: DC Chargers?

#25 Post by boocat » Sun Aug 12, 2018 1:29 pm

I stay confused.

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Henpecked
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Re: DC Chargers?

#26 Post by Henpecked » Tue Sep 11, 2018 12:53 pm

So what is the difference between a marine battery and a UPS battery? I get lots of free used UPS batteries.

Uninterruptible Power Supply. They carry critical electrical loads during power outages and use deep cycle batteries.

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Re: DC Chargers?

#27 Post by Marc K » Wed Sep 12, 2018 6:35 am

I want to avoid diluting this thread about chargers any further than I already have, so I am posting a reply in a new thread.
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