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Old 02-23-2016, 09:39 AM   #1
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charge time using generator

have (4) 6v 420 amph batteries, wondering how long it would take to fully charge them with a small honda generator.
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Old 02-23-2016, 10:21 AM   #2
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i don't know.


but i have the same problem, running the gen to charge the batteries. i have a battery monitor, but with the generator and charger i have, its easy to get the batteries back 80%, that takes about an hour.
the 80-100% charge takes much longer and i dont worry about it with the generator.

part of my problem is a "smart charger". it reads the charge and slows down charging when you get to 80%. its not worth the diesel to try to get it more charged than that

if anyone knows of a "dumb charger" i'd be interested.

plugging in at home the smart charger is great, on the fly, to charge the batteries, its not so great.

good luck
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Old 02-23-2016, 10:23 AM   #3
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I would estimate that it would take between 5 hours to 5000 hours to charge.

Just joshin'. What do you have for a battery charger? How many amps does it put out during bulk charge? How many watts is the generator? There's not enough information here to take a solid guess.
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Old 02-23-2016, 10:38 AM   #4
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Quote:
Originally Posted by turf View Post
the 80-100% charge takes much longer and i dont worry about it with the generator.

part of my problem is a "smart charger". it reads the charge and slows down charging when you get to 80%. its not worth the diesel to try to get it more charged than that

if anyone knows of a "dumb charger" i'd be interested.
There's a good reason for this, Turf. From zero (which a deep-cycle lead acid battery should NEVER be if you plan on using them for more than a year) to about 80% you can charge the batteries at their max charge rate, known as the bulk charge. It is often a percentage of the overall amp hours. I have a couple 155Ah (C/20h) batteries and their max bulk charge is 10% of the amp hours, or 15.5 amps @ 14.7 volts (as found in the batteries datasheet). Any more and you risk damaging the battery.

Once you hit above that 80% mark the amperage needs to be reduced so you don't boil the electrolyte and/or damage the plates. This is called the absorption charge. Looking at the datasheet for my battery shows that the absorption charge can be up to 3% of the amp hours, or 4.65 amps @ 14.7 volts. This is where things slow down, but it's important to do for longevity. Lead acid deep cycles will last longest if they are kept charged between 100% and 80%. In fact, they will last almost twice as long compared to discharging them down to the 50% mark.

After that you can maintain the batteries by applying a lower voltage float charge. 13.02 volts for my batteries.

Again, looking at my datasheet I can see that the best possible scenario for charging the batteries from dead is 9-12 hours. But I have 3 batteries. I would need a 46.5 amp charger to meet that best case scenario. I have a 40 amp charger, so I'm not too far off from the max. It's better to be a bit under than to be over, anyhow.

Cheers
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Old 02-23-2016, 12:55 PM   #5
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when you are plugged in those slow charge rates are fine. but on day #2 of boondocking and you need to recharge the batteries with the generator, that slow charge after 80% seems like a waste of fuel.

my battery monitor show the charge rate, and if it drops below down too low, i just dont see the point.

on the road, i manage my batteries between 50 and 80%. come home and plug in to top it off.

my battery bank is 4 X 110AH deep cycle. and have a 40amp smart charger.

also have a pair of battery monitors one for the house, one for the bus.

this is the house monitor:

showing it at its floating charged (plugged in to the house)



and this screen shows that the battery is 95%, charging at .1 amp and will take at least 199 hours of that to bring it up to 100%





199 hours of gen time is not acceptable

i want a dumb charger


i charge about 1-2 hours a day, and that keeps me around 80%. as the charging amps drop, the hours required go up and the smart charger cant recharge to 100% in a day
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Old 02-23-2016, 01:33 PM   #6
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I tried using a dumb charger on a deep cycle battery once and pulled it off once I started seeing smoke, or steam, or whatever it was coming out the top of the battery. The charger was an analog car battery charger. All anecdotal, but I personally won't be trying that again.

It seems to me that the smart charger is way under the amps that it could be charging at. As mentioned previously, my battery bank can be charged at 13.95 amps max for the absorption charge. Your bank is probably similar. Can you change the absorption charge rate in the charge controller's settings? 0.1 amps is almost meaningless.


I know this becomes a contentious issue with a lot of folk, but this would be a situation where a couple solar panels would come in handy - even small ones - to pick up where the generator leaves off. It's worth weighing the cost, anyhow.

For example:
$??? for solar panels to bring the batteries from 80% to 100% so they last 5 years, or
$??? for new batteries in 2-3 years...
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Old 02-23-2016, 01:48 PM   #7
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I kind of doubt whether a dumb charger will do much better for you. It'll still work on principles similar to what jazty wrote. Chargers are limited in both voltage and current. The bulk charge often happens in a "constant current" mode in which the charger puts out its 40 amps or whatever is its maximum, and the battery's voltage rises as it charges. At some point the battery voltage rises to a point where the charger switches from constant current to constant voltage mode. That's probably around 13.8-14.5 volts for a 12-volt lead battery. From this point on the charging current tapers down, whether it's a smart or dumb charger. As I understand it, the difference in smart and dumb chargers is that the dumb has a single switch-over point from constant current to constant voltage whereas the smart charger has the three modes (bulk, absorption, float) with different current and voltage limits for each. It wouldn't surprise me for the smart charger to actually do the job faster because it can be more aggressive during the bulk phase and then back off for absorption.

When is most of your battery power used? If it's overnight, then maybe you could run the generator first thing in the morning to get the bulk charge taken care of, then leave a solar panel on it the rest of the day to do the absorption part. Because the current needed for absorption is inherently so much lower, the solar array that provides only absorption and float could be much smaller than an array that also has to do bulk charging.
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Old 02-23-2016, 01:54 PM   #8
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Well said, Family Wagon!

As I was reading the US Battery 12v XC2 datasheet I was also learning about constant current in bulk charge and constant voltage in absorption charge, but didn't feel confident in explaining it
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Old 02-23-2016, 02:55 PM   #9
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The BM-1 manual does mention "If the BM-1 is left for long periods registering little or no charge or discharge current, the estimate of capacity may become unreliable. It is important to switch some load onto the battery for a few minutes so a reliable estimate can be calculated, and its value settles, before starting charging." Could that be at play here? It's a possible explanation for why the charger believes the battery is full (as evidenced by the 0.1 A charge rate) but the monitor shows only 95% state of charge.

Maybe verify that the connections to the battery, shunt, and charger are all clean. A dirty connection creating extra voltage drop could result in the battery being under-charged or at least charging more slowly than necessary.

Quote:
Originally Posted by jester View Post
have (4) 6v 420 amph batteries, wondering how long it would take to fully charge them with a small honda generator.
jazty is right, more numbers are needed. As a weak comparison point, I ran an EU2000i powering a Black & Decker 40 amp charger into a pair of Trojan J305-AC (I think) with 305 AH rating, but these were previously used and certainly reduced capacity. I don't know what state of charge I even began charging at, but I'm guessing 60%.. anyway, it was "mostly" charged in 2-4 hours.

If you were thinking of charging those batteries directly with the "12 volt battery charging" output from any generator, Honda or otherwise... don't. That output is completely unregulated and will either never finish the charge or will over-charge. It's also really slow. From an EU2000i you can pull 1600 watts on the AC output, but only ~100 watts (I think it's labelled 8 amps?) on the 12-volt output.

Charge time on a generator is the same as charge time with the same charger plugged into the wall at home.
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Old 02-23-2016, 03:27 PM   #10
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ive had lights on and off in there recently so i don't think its idling and not registering. I've seen it happen, after sitting, and putting a load on the batteries, a new reading will occur. thats not the case here.

my charger is a progressive dynamics, and it has a hand held pendant that cycles through the charge modes if you want to change what it is doing.

you can override the automatic charging mode for a bit, but the battery monitor lets you know when its gone back to its float charge.

rarely do i get the batteries up to 100%. the truck battery is more likely to be there than the coach.
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