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Battery charging with solar/engine


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I wonder if anyone wouldn't mind helping me try and work out how much of a charge my solar panels can give in theory / what they did today. I'm very much a novice!  

I did a power audit that gives a fairly generous estimate of 95.5 AH a day. We have 500W solar panels and a beta marine 43 engine with (i think) a 45 A alternator. We 4 Trojan 6v T105s wired up to give two 12v batteries each 225A. On this cloudy day my Tracer MT50 unit tells me we got 0.18kwh charge energy.  

Is there a way I can tell how much charge my solar panels gave the batteries today with these numbers? I've been scratching my head and can't work it out... 

How can I estimate how much charge the solar panels would give on a sunny day? And on cloudy days can I estimate how long I would need to run the engine for? 

 

Sorry for all the questions! I'm not even sure if it's possible to work it out with the numbers I have given but thanks in advance if you read this far :)

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100 AH at 12 volts is 1200 Wh or 1.2 kWh per day.

A 500 W solar panel would generate 0.5kWh in an hour on a really sunny day, so in summer you should have no problem keeping the batteries charged.

Your 0.18 kWh on a cloudy day sounds very low.  Either it was a VERY cloudy day, or your batteries were aleady fully charged, and so the available solar energy had nowhere to go. 

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There is a big difference between full sun, cloudy bright, cloudy dark and shade charging performance. The difference can easily be a factor of 10, in full sun you should get 25+ amps in the middle of the day, but cloudy and in shade you may only get 2.5 amps. The amount of charge also depends on the state of the battery bank, if below 70% then the above 25 amps should occur if the battery is over 90% full then it will limit the current to maybe 5 or 6 amps even though your panels are in full sun. This is just the same as the alternator the last 20% of charge takes a long time.

2 minutes ago, David Mack said:

Your 0.18 kWh on a cloudy day sounds very low.  Either it was a VERY cloudy day, or your batteries were aleady fully charged, and so the available solar energy had nowhere to go. 

Wot he said

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How old is your Beta 43 engine? I'd be very surprised if the alternator was only 45A and unless it's really old, it will have 2 alternators with perhaps 45A for the engine battery and 100A to 175A for the domestics.

The thing with solar is that it's great for perhaps 9 months of the year, for the other 3 months you get virtually nothing, so you need to have a strategy for the depths of winter.

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Thanks for all your replies! The MT50 meter tells us the voltage in the batteries as well. This week by the time I get home at 7pm it's usually between 12.6-12.5, down to about 12.3 before bed and when I wake up at 7am it's down to about 11.9/12. But gradually over the week it's been getting lower, so when I get home it was 12.7 on Monday, 12.6 Tuesday, 12.5 today 

It has been quite cloudy but we are also moored next to a tree so are quite a bit shaded, would this explain why only 0.18kw? I think our batteries are getting discharged enough to need a decent charge. 

Our engine is 2001 I believe, and your right, from the manual I think it has a 175A for domestics but I haven't checked for sure. 

Sorry for my ignorance! I'm slowly learning, started off not knowing anything at all i.e I had no idea how a battery works

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9 minutes ago, hopefulboaterlndn said:

Thanks for all your replies! The MT50 meter tells us the voltage in the batteries as well. This week by the time I get home at 7pm it's usually between 12.6-12.5, down to about 12.3 before bed and when I wake up at 7am it's down to about 11.9/12. But gradually over the week it's been getting lower, so when I get home it was 12.7 on Monday, 12.6 Tuesday, 12.5 today 

It has been quite cloudy but we are also moored next to a tree so are quite a bit shaded, would this explain why only 0.18kw? I think our batteries are getting discharged enough to need a decent charge. 

Our engine is 2001 I believe, and your right, from the manual I think it has a 175A for domestics but I haven't checked for sure. 

Sorry for my ignorance! I'm slowly learning, started off not knowing anything at all i.e I had no idea how a battery works

Sounds like you need to supplement the solar with a bit of engine charging (or other) on the cloudier days(or use less electricity). Definitely plan for winter if you have no mains hookup. 

 

Either that or pray for some sun:)

 

The other option would be to chop down the tree, move the panels or move the boat. 

Edited by rusty69
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11 minutes ago, hopefulboaterlndn said:

Thanks for all your replies! The MT50 meter tells us the voltage in the batteries as well. This week by the time I get home at 7pm it's usually between 12.6-12.5, down to about 12.3 before bed and when I wake up at 7am it's down to about 11.9/12. But gradually over the week it's been getting lower, so when I get home it was 12.7 on Monday, 12.6 Tuesday, 12.5 today 

It has been quite cloudy but we are also moored next to a tree so are quite a bit shaded, would this explain why only 0.18kw? I think our batteries are getting discharged enough to need a decent charge. 

Our engine is 2001 I believe, and your right, from the manual I think it has a 175A for domestics but I haven't checked for sure. 

Sorry for my ignorance! I'm slowly learning, started off not knowing anything at all i.e I had no idea how a battery works

At 7pm in the summer (which, it seems, is not now!) there will still be some solar charge available, which will push the voltage up a bit. Therefore the voltages you are mentioning represent batteries not fully charged by the end of the day, and nearly flat in the morning. As a guide, you don't want to go below about 12v under light loads, and more importantly, if you persistently fail to fully charge the batteries you will rapidly kill them from sulphation. I note you have Trojan T105s which are good batteries, but do require charging at highish voltage towards the end of the charge, ie 14.8v or more. If you carry on with this charging regime, the batteries will become badly sulphated and lose most of their capacity in a few weeks.

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Yes sorry I do realise the solar isn't doing enough I was trying to work out if by how much. Maybe that's not really important, just need to figure out how I'm going to get more juice in the batteries. getting home at 7 only leaves me an hour to run the engine... looks like we'll be moving! 

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40 minutes ago, hopefulboaterlndn said:

Yes sorry I do realise the solar isn't doing enough I was trying to work out if by how much. Maybe that's not really important, just need to figure out how I'm going to get more juice in the batteries. getting home at 7 only leaves me an hour to run the engine... looks like we'll be moving! 

Yes. The important bit is to know is when you must run your engine and when you can stop running it, this will clearly increase as the days get shorter (all other things being equal). 

 

Edited by rusty69
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I dont know the answer in watts. It was stupidly cloudy yesterday.

I have 330Ah battery bank, which is good for 12 hours of my normal usage (think TV being on most of the day or night). My fridge freezer seems to use about 5 or 6 amps & is mostly on, I guess its old & tired. My desktop PC with 2 monitors will use about 15A browsing the internet, or if I'm gaming can easily pull 25A.

My 660W of solar at maximum can put out 48A.

December 18th 1 year we had no cloud all day, & whilst I cant remember the numbers, I did work out at the time that the solar put out enough to run my fridge for 8 hours.

Those 3 days of stupidly hot sunny weather, I remember waking up at 9.45 to find my batteries on float.

Yesterday was abysmal, stupidly cloudy. Pretty much all day the solar was only putting out 0.6A (+/- 0.1), the highest it got to was 2.6A briefly. So I was running my engine for electric, some nob commented on how I shouldnt need to because of all the solar panels I've got, apparently he didnt seem to think sun was needed for them to work.

This morning, even though it's cloudy, you cant look at where the sun is supposed to be in the sky because it's too bright, & my solar is putting out about 10A.

Brightest part of the day about 5pm yesterday, FOTRN mooring Doddington, River Nene (lit the fire as well in the morning cuz it was cold!)
b1WJs3B.jpg

Edited by Ssscrudddy
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There are plenty of helpful replies on here so far. My twopenneth as a full time liveaboard of many years experience most of it as now off grid. Solar are a great  help IF and WHEN mr solar is out to play but even then I would be suprised that unless a cave dweller type boater the solar will be enough for your use. I use my engine every day of the year for between 1 and a half and four hours, I only have 200 watts solar tho but the engine alternator is my main source of charge. You will kill your trojans very rapidly if you do not change your charging regime they last no longer than cheapos if not shown love and affection and tucked up in bed every night. Thing is nothing is for nothing so do you wear your expensive engine like me happily as it works the best or do you not charge batteries enough and replace every six months? or change job allowing earlyier home arrival or find a mooring with a plug in or, or. or ,or etc etc etc?

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On 30/06/2017 at 05:24, hopefulboaterlndn said:

Yes sorry I do realise the solar isn't doing enough I was trying to work out if by how much. Maybe that's not really important, just need to figure out how I'm going to get more juice in the batteries. getting home at 7 only leaves me an hour to run the engine... looks like we'll be moving! 

 

I have almost this exact problem too. No problem for nine months of the year but in the three winter months solar output is effectively zero. Mine's worse though as I tend to get home after 8pm so no time at all in the week to charge. There are three answers, 

1) Get a mooring with mains power to run a battery charger
2) Get a truly silent generator installed so you can run it out of hours
3) Pick one of the above 

The solution I settled on which turned out not to work was get a battery bank big enough to last a week between charges. It turns out batteries will knacker themselves if not charged every day. You will probably be ok (just about) with an hour a day (if you do it religously) plus six or eight hours at the weekend. My Trojanoids goosed themselves in about three months of leaving them a week between full charges. 

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3 minutes ago, Mike the Boilerman said:

 

I have almost this exact problem too. No problem for nine months of the year but in the three winter months solar output is effectively zero. Mine's worse though as I tend to get home after 8pm so no time at all in the week to charge. There are three answers, 

1) Get a mooring with mains power to run a battery charger
2) Get a truly silent generator installed so you can run it out of hours
3) Pick one of the above 

The solution I settled on which turned out not to work was get a battery bank big enough to last a week between charges. It turns out batteries will knacker themselves if not charged every day. You will probably be ok (just about) with an hour a day (if you do it religously) plus six or eight hours at the weekend. My Trojanoids goosed themselves in about three months of leaving them a week between full charges. 

Gosh wow three months!! Okay that's not an option. We haven't got a generator yet but I've been looking into it, people seem keen on the Honda's but my guess is they'll still make a fair amount of noise 

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On 30/06/2017 at 10:18, hopefulboaterlndn said:

Gosh wow three months!! Okay that's not an option. We haven't got a generator yet but I've been looking into it, people seem keen on the Honda's but my guess is they'll still make a fair amount of noise 

It can easily turn into a deal breaker for living on a boat off grid. Treat this problem seriously.

Hondas are exactly the sort of genny you CANT run after 8pm. An inboard cocooned diesel genny is what you need. Very expensive but does the trick. Just about. 

Another approach is just buy new batteries regularly. 

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8 minutes ago, Mike the Boilerman said:

It can easily turn into a deal breaker for living on a boat off grid. Treat this problem seriously.

Hondas are exactly the sort of genny you CANT run after 8pm. An inboard cocooned diesel genny is what you need. Very expensive but does the trick. Just about. 

Another approach is just buy new batteries regularly. 

When you say very expensive, how much is that? Just been on the beta website but they don't publish prices. Need a ball park to work out if this is something I could save up for or not 

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1 minute ago, hopefulboaterlndn said:

When you say very expensive, how much is that? Just been on the beta website but they don't publish prices. Need a ball park to work out if this is something I could save up for or not 

£7000-£10000 will get you a reasonable diesel cacooned generator installed.

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