How long will it take to charge my batteries?

[Chuck Hawley]

At the risk of being labeled a nitpicker, can we agree to not use the term "amps per hour" which is nonsensical? I know that most people will understand what is meant by amps per hour, but I think it hurts our collective understanding of what goes on in an electrical system when we mangle the units of measure.

Chuck

[muttskie]

[QUOTE i have met many males who cannot understand this concept.
good luck.[/QUOTE]

Ha ha ha, good one...

[RainDog]

Originally Posted by AFKASAP

Thank you for your reply. That makes sense. It seems quite a long time to charge the batteries. Is my charger particularly small?

Your Honda will run a much larger charger, and that will shorten your time to go from 50% to 80%, but once you get above 80% or so, your charger is not putting out full power anyway, so it will not make a difference on the tail end. If you will be charging with your generator on a regular basis, it is probably worth up-sizing your charger. If only occasionally, it is probably not worth it.

[hellosailor]

"both the service and starter battery are on around 13.7v."
That is called a "surface charge" and represents the unmixed electrolyte after the alternator or charger has just been shut. Put a spotlight or other load on for 5 minutes and look again, you'll see 12.7-12.8 volts for new batteries, less for older ones. The exact numbers vary for the exact make of battery, but somewhere around there is the best you'll ever get. And that's assuming you have a calibrated voltmeter.
After that, each loss of 0.1 volt represents a loss of about 1/10th of the useful voltage, so if you have a nice new battery that shows 12.7 volts fully charged? Then about 12.2 would be half charged, and time to charge 'em back up again.

" How low can I discharge my batteries before I risk damaging them? "
SLI (starting, lights, ignition) can be killed in as few as 4-6 full discharges. Deep cycle batteries vary, but generally you can get more life out of them by only discharging them 30%. Not too bad at 50%, although you won't get the same number of cycles out of them. Each manufacturer claims a different number, but you might find one saying 1000 cycles at 30% and only 100 cycles at 90%. Whoever made your batteries can give you their promises.

[Cheechako]

Originally Posted by AFKASAP

My control panel has an lcd display that shows the voltage of the batteries. I normally see both the service and starter battery are on around 13.7v. How do I know when my batteries are at 60% or 50% or 40% etc?

How low can I discharge my batteries before I risk damaging them?

As mentioned there is no good formula for charge time as it depends on variables. Battery condition, charger curve etc. Because of this the table below is as good as anything. Normally a new rested battery will be about 12.45 volts fully charged.
The good news is you will learn fast how your battery bank/charger work out.

[a64pilot]

I am going to assume you have flooded batteries, if so this is a good site to "root" around and learn on.
For example all the voltage / depth of discharge charts are I believe at 0 load, any load at all will lower the voltage, but you will be conservative, meaning your erring on the safe side.

Battery Maintenance | Trojan Battery Company

[jwcolby54]

Originally Posted by Chuck Hawley

At the risk of being labeled a nitpicker, can we agree to not use the term "amps per hour" which is nonsensical? I know that most people will understand what is meant by amps per hour, but I think it hurts our collective understanding of what goes on in an electrical system when we mangle the units of measure.

Chuck

Chuck, there is nothing nonsensical about it. It is a convenient shortcut for the more complex reality. And as background I fixed entire computer systems for the USN.

I have an led light. At some instant in time my battery is putting out a specific voltage but an instant later the voltage is different. So the led pulls some specific current, but only for that instant. Damned inconvenient!

So let's agree to assume that my battery puts out 12v and be done with it. Now I look at my led light which pulls 1 amp at 12v and multiply by the time I have the light on and voila I have amp hours used. I can add my little ice box (6 amps) and that light (1 amp) and say that I am using 7 amps per hour.

I actually care about that because my battery appears to say that it will provide x amps for y hours. If I can get close to the number of amps I am pulling I can approximate how long I can use my light.

Is that EXACT? no because the entire Damned time the voltage was changing (dropping most likely). Is it close enough to be useful?

It is for me. I now have a ballpark figure for my current usage.

Now if you want to have a scientific discussion OK we can move away from that. But the op specified that he was ignorant of the subject. So let's cut him some slack.

[Paul Elliott]

Originally Posted by jwcolby54

Chuck, there is nothing nonsensical about it.

Chuck is completely right.

Originally Posted by jwcolby54

[...]
So let's agree to assume that my battery puts out 12v and be done with it. Now I look at my led light which pulls 1 amp at 12v and multiply by the time I have the light on and voila I have amp hours used. I can add my little ice box (6 amps) and that light (1 amp) and say that I am using 7 amps per hour. [...]

No, you can say you are drawing 7 Amps when these devices are turned on. If you leave them on for one hour they have drawn 7 Ah. Leave them on for 2 hours, it's 14Ah.

We had a multi-page, multi-week argument / discussion about this some time ago: http://www.cruisersforum.com/forums/...hr-154363.html
I don't know that it changed anyone's mind, but "Amps per hour" is not a term that we should be using when talking about battery loads. It *does* mean *something*, but probably not what you think.

[dlymn]

Your generator is a 2kilowatt unit (?). Your current charger provides 300 watts/hour. This suggests that you are underutilising the charging potential of the generator. If you drew only 1000 w/h, you would not be overworking your generator. This might mean that you could run an 80 amp charger without stressing the gennie. I don't know whether your batteries an cope with that sort of load, but if they can, having an 80 amp charger would significantly reduce charging time. The Honda GX100 80 will do this but might need some fairly heavy cables. 110/240 volt battery chargers at this rate are pricey.

[StuM]

Originally Posted by jwcolby54

Chuck, there is nothing nonsensical about it. It is a convenient shortcut for the more complex reality. And as background I fixed entire computer systems for the USN.

I have an led light. At some instant in time my battery is putting out a specific voltage but an instant later the voltage is different. So the led pulls some specific current, but only for that instant. Damned inconvenient!

So let's agree to assume that my battery puts out 12v and be done with it. Now I look at my led light which pulls 1 amp at 12v and multiply by the time I have the light on and voila I have amp hours used. I can add my little ice box (6 amps) and that light (1 amp) and say that I am using 7 amps per hour.

I actually care about that because my battery appears to say that it will provide x amps for y hours. If I can get close to the number of amps I am pulling I can approximate how long I can use my light.

Is that EXACT? no because the entire Damned time the voltage was changing (dropping most likely). Is it close enough to be useful?

It is for me. I now have a ballpark figure for my current usage.

Now if you want to have a scientific discussion OK we can move away from that. But the op specified that he was ignorant of the subject. So let's cut him some slack.

JC You are wrong
Please search the forums for the thread "Amps v Amp hrs v Amps per hr" (or somehthing like that Im on a mobile and cant search for the link easily)
It is when people like you incorrectly refer to 7 Amps per hr that people like the OP get confused. Your ice box and lamp draw 7 Amps. They consume 7 Amp hrs per hour.

Sent from my SM-G900I using Cruisers Sailing Forum mobile app

[monte]

Regarding the SOC, it's a good idea to check the manufacturers data for the specific battery. My flooded cell batteries have quite different SOC voltages to the 'normal' voltages posted above.

[StuM]

Originally Posted by dlymn

Your generator is a 2kilowatt unit (?). Your current charger provides 300 watts/hour. This suggests that you are underutilising the charging potential of the generator. If you drew only 1000 w/h, you would not be overworking your generator. This might mean that you could run an 80 amp charger without stressing the gennie. I don't know whether your batteries an cope with that sort of load, but if they can, having an 80 amp charger would significantly reduce charging time. The Honda GX100 80 will do this but might need some fairly heavy cables. 110/240 volt battery chargers at this rate are pricey.

No. It provides 300W regardless of time. Please refer to the thread linked above

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[dlymn]

Quite right StuM. 300 watts become 25 amphours at 12 volts on the battery side.
However, this site might muddy the water a little http://www.energylens.com/articles/kw-and-kwh

[smac999]

keep in mind your 25a charger is putting 25a into the boat, not into the batteries. a few lights on or nav gear and it's not hard to have 10-20a used on the boat. now you are only putting 5a into the batteries. and it'll take all day.


if you are running a gen to charge batteries. get the biggest charger it'll run to reduce the gen run time. you'll never fully charge a battery with a gen. instead of going from 50%-100% once a day. go from 50%-75% twice a day. (same battery useage, 1/3 the total gen run time.

[smac999]

Originally Posted by AFKASAP

My control panel has an lcd display that shows the voltage of the batteries. I normally see both the service and starter battery are on around 13.7v. How do I know when my batteries are at 60% or 50% or 40% etc?

How low can I discharge my batteries before I risk damaging them?

battery monitor like a victron 700