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Old 29-03-2015, 02:38   #1
tat
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Using a 40amp charger for an hour. Ok?

The idea is for me to buy a silent Honda 900watt gen, and use a 40amp charger to boost the batteries for no more than an hour to keep them topped up when they have got a bit down.

But there is a lot written about smart chargers, and how you can overcharge.

From my reading, I gather that the first bit of charge goes in easy, so you can get easily to 90%. The last 10% is harder to reach because of internal resistance to being charged. But I don't need that last 10%. 90% will do me fine, as I can easily charge the batteries back to 90% with just a quick 40amp one hour boost, so I will always have reasonably-charged batteries whenever I want, ie I will always have the electricity I need, and only need to run a generator for an hour at a time because I only need to get them to 90%.

That is the idea. But my question is will I over do them? I'm thinking of buying a Sealey 40amp charger/starter, the Boost 180. I assume this is not a smart charger. But I should be ok if I only do them for an hour? I'm a bit new to all this, and the charger i have used for my bike and car has been a 4amp, so jumping up to 40amp seems a bit daunting, so I just want to check with you whether I am doing something daft with my idea. A one hour 40amp boost with a basic unsmart charger. Can't do any harm? I'll be using sealed batteries, so can't be checking acid level.

PS... I've just checked the spec of the 900watt gen and it says output at 12v is 8amps.......surely that means a 40 amp charger would be pointless, and that I would just only be able to use an 8amp charger. I was under the impression that the gen would do a 40amp. What am I getting wrong? I will only be getting a 900watt gen, so what is max charger I can use, please?
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Old 29-03-2015, 03:34   #2
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Re: Using a 40amp charger for an hour. Ok?

I think I get it now, that it would run a 40 amp charger, that the charger can output 40 amps at 12v, although the generator will only do 8 amps by itself, at 12v.

But would the one hour boost do any damage?
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Old 29-03-2015, 03:34   #3
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Re: Using a 40amp charger for an hour. Ok?

Two quick points, other will expand on this for sure .

1. The battery bank will only accept the charge it wants to, i.e. if the battery will only accept say 7.5 amps at its particular state of charge (SOG), then that is all that the charger will deliver whether it's a 10 amp or 20 amp or 40 amp or whatever amp charger. The 40 amp figure you quoted is the maximum the charger will deliver but only if the battery will accept that figure at the SOC in question.

2. The big charger will be plugged into the mains side of the genet set (i.e. the 900W). The charger will need something like 600W at it's rated 40 amp output so yes, the 900W is going to be sufficient. The 12 volt outlet of the genset is only 8 amps and that would normally be used to charge it's own starting battery or whatever.
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Old 29-03-2015, 03:41   #4
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Re: Using a 40amp charger for an hour. Ok?

Hi tat
I have a Honda eu10i great generator but only rated 800watts
continuos. I also run a 40amp charger works well.
Not all chargers are equal some are more efficient than others,
Meaning some may not run on this generator.
You need to find out the power usage of the charger you intend to use ?
Amps are a function of volts divided into watts
eg 1amp at 240volts = 240 watts - at 12 v 240w = 20amps
A watt is always a watt
an amp changes according to the voltage
1a at 240= 240w
1a at 12v=12w
1a at 110v=110w

I hope the above is clear it can be confusing especially at the start.

The Honda puts out 240v x 800w continuos
It will do this on the Eco throttle setting (quieter)
The 12v output is un regulated & needs to run at full
throttle to achieve this (noisy & inefficient)
The best way is to use a battery charger on 240v
The sterling pro charge ultra 12v 40a charger
has a power input requirement of 650w
This is the charger I use.
I am not saying it is the best merely that it will
run on the Honda
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Old 29-03-2015, 05:46   #5
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Re: Using a 40amp charger for an hour. Ok?

The continuous rating of the eu10 is 900 watts. You need to ensure the charger you buy is efficient enough to not overload this rating. Some chargers are inefficient and you can only use around 30 amps mayx output models whereas others like a Sterling ultra pro will are very efficient and have a 60 amp model that can be powered by an eu10.

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Old 29-03-2015, 06:07   #6
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Re: Using a 40amp charger for an hour. Ok?

You don't say how much battery capacity you are trying to charge, but 1 hour at 40 amps is 40 AH.

If your batteries are at 50%, that will bring 1, 100 AH battery up to about 90%.

More capacity then that and you are not reaching you goal.

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Old 29-03-2015, 07:41   #7
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Re: Using a 40amp charger for an hour. Ok?

We also have a 40A charger(ProNautic same as Sterling) run off a Honda 1000 using 110V. It works great. Our battery bank is 450A at 12V.

Just a note: Many of the better battery chargers allow you to dial back the output as a custom setting. So if your small generator is unable to start the battery charger cutting back on the max output should help it to run. The max output will be slightly reduced and that will mean a longer run time in the full output mode.

Good luck

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Old 29-03-2015, 08:43   #8
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Re: Using a 40amp charger for an hour. Ok?

Have you ever considered just putting together a small dedicated DC charging generator/alternator? Figuring 1hp per 25amps of 12v DC power you could easily use a little 4hp engine driving a 100amp alternator and either shorten your charge time or increase your charging ability.

Just a thought.
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Old 29-03-2015, 08:45   #9
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Re: Using a 40amp charger for an hour. Ok?

Be good to your batteries and they will treat you OK. Batteries live longer when not deeply, beyond 50%, discharged and promptly, as soon as you can, recharged to 100%. Charging to 90% of capacity will shorten the life of you batteries. Smart chargers will charge at the required rate and not damage your batteries when left on for long periods.


Since smart chargers 'sense' how great a charge rate the batteries will accept almost any size charger will do. And since batteries will not accept a high rate of charge for very long, less than an hour, you can use a small charger with good results. There is discussion about what rate is good, some say flash or high rate of initial charge is best others thing a slow recharge is best. No matter, charging to 100% is best and 90% ain't.
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Old 29-03-2015, 09:23   #10
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Re: Using a 40amp charger for an hour. Ok?

Quote:
Originally Posted by AlwaysFORSAIL View Post
Be good to your batteries and they will treat you OK. Batteries live longer when not deeply, beyond 50%, discharged and promptly, as soon as you can, recharged to 100%. Charging to 90% of capacity will shorten the life of you batteries. Smart chargers will charge at the required rate and not damage your batteries when left on for long periods.


Since smart chargers 'sense' how great a charge rate the batteries will accept almost any size charger will do. And since batteries will not accept a high rate of charge for very long, less than an hour, you can use a small charger with good results. There is discussion about what rate is good, some say flash or high rate of initial charge is best others thing a slow recharge is best. No matter, charging to 100% is best and 90% ain't.
+1

100% charge as often as possible will prolong battery life considerably. Think about solar in addition to the EU1000i.
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Old 29-03-2015, 09:23   #11
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Re: Using a 40amp charger for an hour. Ok?

Hi I work as a car mechanic and can advise you to use a smart charger if possible they do more than just charge the battery they renovate them and will get them to 100% I use a Ring 16 amp smart charger and disposed of the boost charger .A lot of info is available on wind turbines and charging batterys if you were thinking of a generator for 12 or 24v .Another idea is to buy a pure sine wave inverter charger this will charge your battery 100% and give you ac power for power tools and appliances like fridge or microwave computers .I use this on my liveabord .
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Old 29-03-2015, 09:26   #12
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Re: Using a 40amp charger for an hour. Ok?

Without knowing the total amp-hours of your battery bank nobody can give you a good answer.
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Old 29-03-2015, 09:29   #13
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Re: Using a 40amp charger for an hour. Ok?

Overcharging with Combiners or ACRs The MYTH:
Overcharging Batteries with a Combiner or ACR
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Old 29-03-2015, 09:53   #14
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Re: Using a 40amp charger for an hour. Ok?

Hi. Short answer...YES, your plan will work, and I think it will work well.

The big reason for smart chargers is that they are often just left on all the time, or for hours on end. Thats when real damage can occur to your batteries. I've seen batteries boiled dry from being left charging on shorepower all the time. BTW, the next thing that happens is an explosion, so smart chargers avoid this.

BUT, you are doing most of the work of the smart charger...I assume you are checking your volts, and being aware of you power use. In your case, a 1 hour charge at 40amps is just what you need. As you said, a trickle for a few hours after this would get you up to 100%, but that is not needed. It would be good to get the batteries up to 100% once in a while to eliminate sulfate buildup on the plates.

The honda genset is excellent and quiet. While I agree with the post suggesting you build a dedicated 12 volt charger with a 4hp engine, who really can do something like this? And no way it will ever be as quiet as the honda. In the end it would likely cost more too.

The only improvement to your plan would be to get AGM batteries. They will charger much quicker than lead acid...but when you consider cost, the old lead acid battery is still all most of us require.

And finally, if you have two banks, or just two batteries, get 2 chargers...one charger on each battery. You'll get a better, faster charge than doing them together, plus you have a reduntant backup.
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Old 29-03-2015, 12:44   #15
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Re: Using a 40amp charger for an hour. Ok?

Harbouring;

What information are you bassing your assumptions on?

How do you know 40 amps is enough?

AGM batteries do not simply charge quicker. They are able to accept more current, then wet cell, but you may need the bigger charger to produce that current.

If the charger is sized properly, for a given wet cell bank, switching to AGM will show little gain.


AGM batteries do accept current to a higher capacity, before tapering off, but they do not tolerate, less then 100% charge cycles very well. (Something the original poster wants to do )

Just wondering



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