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How long to charge batteries?


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There are far too many unknowns to give a proper answer, but assuming you have an alternator with a good output (actually able to produce lots of amps and set to a suitable voltage) typical charge times are:

 

2 to 3 hours to get a reasonable charge into the batteries that will keep you going till the next recharge.

7 to 8 hours to get the batteries right up to 100%, and this must be done every week or two if you want a good battery life.

 

.............Dave

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its a 175 amp alternator.

What do you mean by "charge"? Because at face value the answer is 0.0001 nanoseconds - as soon as you run the alternator the battery will charge. If you meant to say "fully charge" then you will have to define what you mean by that since the answer will vary dramatically according to that definition.

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To 80% will be quite quick though - it's the very important last bit that takes the time. I'd recommend you avoid going as low as 50% if you can too if you want to eek out the maximum life from your batteries.

Out of interest how long if Glynn substituted his 175 alternator for two 100w solar panels sitting on the roof on a decent sunny day not costing a penny in diesel.

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Out of interest how long if Glynn substituted his 175 alternator for two 100w solar panels sitting on the roof on a decent sunny day not costing a penny in diesel.

 

 

Pretty much the optimal solution might be a (relatively) early morning cruise (accompanied initially by the smell of impending bacon sandwich perhaps), before mooring up with a full tank of hot water and batteries back up to 80% or so, followed by a relaxing afternoon whilst the solar generates the lesser current over the longer period to top the batteries off. icecream.gif

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What do you mean by "charge"? Because at face value the answer is 0.0001 nanoseconds - as soon as you run the alternator the battery will charge. If you meant to say "fully charge" then you will have to define what you mean by that since the answer will vary dramatically according to that definition.

 

OK "Fully Charge"

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OK "Fully Charge"

Yeabut I did mention that you'll have to define what you mean by "fully charged" since practically speaking, there's no such thing.

 

Fully charged according to an out-of-the-box Victron monitor (4% tail current) is a very different proposition to fully charged according to me (about 0.5% tail current). The difference is many hours.

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Yeabut I did mention that you'll have to define what you mean by "fully charged" since practically speaking, there's no such thing.

 

Fully charged according to an out-of-the-box Victron monitor (4% tail current) is a very different proposition to fully charged according to me (about 0.5% tail current). The difference is many hours.

This is what I aim for. Edit its a 24 volt system

post-261-0-77262900-1469738096_thumb.jpg

Edited by ditchcrawler
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Ok well anyway, while you're at it please could you tell me how long a piece of string is?

 

But if you ask me which piece of string, I might sulk.

depends whether the knots on the string are proper knots or ....knot.

  • Greenie 1
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With my 80A inverter charger, I tend to find if I have used say, 240Ah over 2 or 3 days, it runs at 80A for a couple of hours, then the amps drawn tend to half every hour, such that the third hour would average 60A, the fourth hour 30A, and so on. I also find it takes more than 240Ah to reach a tail current of about 4A, (in a 400Ah bank Trojan T105s).

 

I've not analysed how much more than my useage has to be put back in to reach fully charged... If on board from say Wednesday evening to Sunday afternoon, (4 nights), my ideal charging regime is a couple of hours Saturday evening, then 5 or 6 hours on a Sunday.

 

I'm pretty sure my alternator is about 55A, but I rarely see more than about 35A on the NASA BM2 monitor.... I've thought about a different pulley ratio, but cant be bothered.

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It doesnt matter.

 

 

It does really, because 'fully charged' is a state no battery ever achieves. The closer it gets to 'fully charged', the slower the charging gets so at some point you have the take a view and call it 'fully charged' even though it isn't.

 

So what Nick is really asking is 'how close to ''fully charged' do you want to get?'.

 

It's quite a challenging question because it forces you to think about the technical issues properly.

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OK, after a days sailing today running time 8 1/2 hours.

The batteries were reading 12.9 volts 45 minutes after switching off the engine, the only electric used since that has been 15 minutes TV and charging a mobile phone and the voltage is now reading 12.3 volts and thats after only 2 1/2 hours from switching off the engine.

 

Thoughts ?.

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OK, after a days sailing today running time 8 1/2 hours.

The batteries were reading 12.9 volts 45 minutes after switching off the engine, the only electric used since that has been 15 minutes TV and charging a mobile phone and the voltage is now reading 12.3 volts and thats after only 2 1/2 hours from switching off the engine.

 

Thoughts ?.

Sounds like new batteries time, I fear.

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OK, after a days sailing today running time 8 1/2 hours.

The batteries were reading 12.9 volts 45 minutes after switching off the engine, the only electric used since that has been 15 minutes TV and charging a mobile phone and the voltage is now reading 12.3 volts and thats after only 2 1/2 hours from switching off the engine.

 

Thoughts ?.

I'm sure you think me pedantic and awkward but you haven't given us enough info to be conclusive.

 

You ran the engine for 8 1\2 hours but what was the charging voltage? Perhaps the charging was good, in which case the batteries are majorly goosed. Or perhaps the charging was marginal, eg a blown alternator diode that brought the charging voltage barely past 13v. The 12.9 sounds good but after 45 mins of no load I think I'd expect more.

 

You'll need to run the engine and report the charging voltage after several hours before we can know whether to address a charging issue or a battery issue (or both).

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I regularly see lots of electricity being made by my solar panels but batteries full so nowt going in!! then fridge kicks in, and batteries not needed as solar does it instead bliss sheer bliss

Edited by peterboat
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