Batteries and living aboard

[MtB]

Ok, this isn't a question exactly, more like an attempt to clarify my thoughts about batteries and living aboard and how to manage charging them.

 

My rough and ready power audit tells me I use approximately 25Ah a day. My pair of 110Ah leisure batteries which I bought in about September appear totally knackered (assuming the SmartGauge is telling the truth). In the morning the SG will typically say 30% charged. Assuming I have time before buzzing off to work I charge them for a couple of hours and this drags them up to about 70% or so. Then when I get home at say 8pm and turn on the laptop and radio they plummet again. If I'm not near anyone I'll run the engine or the genny again to top up.

 

But the thing is, it is becoming clear to me that even if I got a Big Fat set of batteries that will last me all week and a Big Fat charger to fill them up again at the weekend, the charging properly to 90% might typically take about 10 hours, but to get to the 100% needed might take 20 hours.

 

Yes a 40 Amp 24v charger will stuff 60% of the charge back in over two or three in the bulk charge phase but it seems once the battery voltage rises to 14.8v and absorption charging is reached, charging to the point where the tail current falls to the nominal 1% cannot be hurried. It simply takes a flippin' long time. And I just don't spend enough time on the boat during the hours of 8am to 8pm to get those charging hours in. And nor would want to spend the whole of my weekends on the boat with the genny running if I'm not cruising.

 

So, it seems to me I either have some good batteries and spend every daytime hour I'm present on the boat with either the engine or a genny running, OR I just buy cheapo batteries and bulk charge them a few dozen times until they expire then buy more.

 

Or is there a better way?

 

(Ok so there was a question in the end )

[by'eck]

Between two and max four hours cruising (or equivalent from equal size charger) always has mine fully charged as long as only overnight use. Its a matter of large enough charge current being available. Try as much as one third (C/3) of batteries amp hour rating - even Gibbo admitted to using such high rates as a trade off between minimal charge times and battery longevity.

 

Would suggest at least a 50 amp multi-stage charger with your 2 x 110 ah batteries if running from genny. Its your present charge regime that has ruined the present ones through a downward spiral. They must be charged to within spitting distance of 100% SOC regularly - at least once/twice a week.

 

ETA: This suggestion will promote horror in the minds of some. However the regime has worked well for me over nearly 20 years including nearly a month at sea relying on generator alone. Remember that whatever max charge current is available the chargers voltage control and batteries themselves will limit the charge current they take, and that once fully charged (or very nearly so) will drop back to a safe float voltage.

Edited January 14, 2016 by by'eck

[nicknorman]

Firstly, bearing in mind Tommy's thread, I'd check the voltage reading on the Smartgauge against a DVM on the terminals. If the voltage is reading within 0.05v the SoC will be accurate. If not...

 

 

You have 110AH and a 40A charger, ie 36% of capacity

 

We have 450AH and a 175A charger (engine alternator), ie 39% of capacity.

 

So very similar.

 

Our batteries may be down at 60% of a morning due to heavy use but, on the rare days we remain static out on the cut, I find a couple of hours per day (hour in the morning, hour in the evening) belts a lot of charge back in and whilst it won't get to 100% it will get to high 80s or low 90s for the start of the evening. We tend to do that for no more than a couple of days before cruising again but I suppose we seem to be able to bulk charge quicker than you.

 

Connections between charger and batteries? (Ie what voltage drop in + and - connections between charger and batteries?

 

Solar? (Ok maybe not right now)

 

The other thing to consider might be the regulation of the charger, ie at what voltage does the current start to decrease? Obviously it doesn't maintain 40A to 14.8v, but with "soft" (ie low gain) regulation it will reduce earlier, perhaps still in the 13.x range. With "harder" (higher gain) regulation it might get to mid -14s before the current reduces. Perhaps the regulation is unduly soft?

Between two and max four hours cruising (or equivalent from equal size charger) always has mine fully charged as long as only overnight use. Its a matter of large enough charge current being available. Try as much as one third (C/3) of bateries amp hour rating - even Gibbo admitted to using such high rates as a trade off between minimal charge times and battery longevity.

 

Would suggest at least a 50 amp multi-stage charger with your 2 x 110 ah batteries if running from genny. Its your present charge regime that has ruined the present ones through a downward spiral. They must be charged to within spitting distance of 100% SOC regularly - at least once/twice a week.

Don't forget he has a 24v system so it's only 110AH

[by'eck]

Thanks Nick - missed that.

 

Would suggest running charger until it drops to float, that its set to one of the higher absorb voltages - say 29.6v as long as lead/acid, even if sealed. Might be worth increasing battery capacity even though it would probably mean doubling it with your installation. Your calculated usage will likely be more and the lesser DoD will aid battery longevity, i.e. spend money to save in the long run.

Edited January 14, 2016 by by'eck

[MtB]

Firstly, bearing in mind Tommy's thread, I'd check the voltage reading on the Smartgauge against a DVM on the terminals. If the voltage is reading within 0.05v the SoC will be accurate. If not...

 

 

You have 110AH and a 40A charger, ie 36% of capacity

 

 

No,I have a 15Amp 24v charger now. I was confusing perhaps when I said perhaps I should get a 40a charger.

 

With batteries AND alternator installed under the floor, nothing is easy where diagosis is concerned. I/m considering moving the batts to say the back cabin, in an easily accessisble position.

 

This is only a problem this time of year. Once the solar gets some traction, it keeps up happily with my power consumption for nine months of the year.

 

In addition, I need to work during the day as I have queues of punters with busted boilers, so lifting floors when I get home tired and in the dark just doesn't happen!

 

I guess I'm trying to design in my head a system that will work for me, rather than diagnose faults in what I have. Once I know what I want/need, I can set about installing it. But I'm far from convinced it exists...

[OldGoat]

deleted

 

Edited January 14, 2016 by OldGoat

[nicknorman]

No,I have a 15Amp 24v charger now. I was confusing perhaps when I said perhaps I should get a 40a charger.

Ah right, missed that. And then I went on to waffle on about a 12v system! Doh!

 

Anyway, get a bigger charger! But make sure the genny can power it.

Edited January 14, 2016 by nicknorman

[MtB]

Ah right, missed that. And then I went on to waffle on about a 12v system! Doh!

 

Anyway, get a bigger charger!

 

 

But sir, SIR, doesn't that 'only' speed up the bulk charging phase? Absorption to 1% will still best be measured with a calendar rather than a clock?

 

Just checked the Smartgauge voltage reading with a UNI-T UT203.

 

Smartgauge reads 25.60v right now. UT203 claims 25.41v (on the Smartgauge terminals). Tracer display reads 25.4v

 

Looks like we have another dodgy Smartgauge....

Edited January 14, 2016 by Mike the Boilerman

[WotEver]

 

Or is there a better way?

Mike, with you being away from the boat all day I'd say you're the perfect candidate for some solar. Okay, it won't do much at this time of the year but in a month or two it would be quietly pumping amps into your battery all day long.

 

In the mean time, optimise what you have. Ensure that your charger cables are big enough (measure the volt drop). Thin cables won't prevent the battery from charging fully but they will increase the charging time.

 

110Ah for 25Ah daily usage is a good balance imho so you just need to sort out how to get more back into them as quickly as possible.

 

Lastly, you were going to check the accuracy of your SmartGauge which seems like a good thing to do of late.

 

Edit to say ignore all of the above because by the time I posted it (got interrupted with a phone call) it was redundant.

Edited January 14, 2016 by WotEver

[MtB]

And even more interestingly, now I've screwed it back on the wall and I'm watching it carefully, the SG reading changes every few seconds, randomly displaying 25.60v, 25,70v, and 25.80v.

 

The Tracer display is oscillating between at 25.4v and 25.5v. Solar is charging at between 0.5a and 0.7a.

The sun is out with clouds scudding across it. So the solar could account for the varying values...

 

 

(Edit to add some missing zeros.)

 

 

P.S. WotEver, I have 360W of solar already which performs admirably nine months of the year...

Edited January 14, 2016 by Mike the Boilerman

[nicknorman]

But sir, SIR, doesn't that 'only' speed up the bulk charging phase? Absorption to 1% will still best be measured with a calendar rather than a clock?

 

Just checked the Smartgauge voltage reading with a UNI-T UT203.

 

Smartgauge reads 25.60v right now. UT203 claims 25.41v (on the Smartgauge terminals). Tracer display reads 25.4v

 

Looks like we have another dodgy Smartgauge....

Possibly, but the SG is over-reading by 0.19v if we take the DVM value as spot on. 0.19/25 is 0.76%, stated accuracy is 0.5% so if the DVM is accurate it is out of spec but not by much. I think you would need to corroborate it with something else. Also you need to watch the display for a bit since it only indicates to 0.1v and the display might be dithering between two values, the ratio of which allows you to interpolate. I'm discounting the tracer. It's in a different league to Tommy's which if extrapolated to 24v system would be 0.5v out

 

Anyway, it's over-reading unlike Tommy's, so it will tend to over-estimate the SoC, but not by much. So when it's saying 30% SoC the batteries really are pretty flat.

[WotEver]

P.S. WotEver, I have 360W of solar already which performs admirably nine months of the year...

Yeah, I edited my post to say ignore me ?

[ditchcrawler]

Ok, this isn't a question exactly, more like an attempt to clarify my thoughts about batteries and living aboard and how to manage charging them.

 

My rough and ready power audit tells me I use approximately 25Ah a day. My pair of 110Ah leisure batteries which I bought in about September appear totally knackered (assuming the SmartGauge is telling the truth). In the morning the SG will typically say 30% charged. Assuming I have time before buzzing off to work I charge them for a couple of hours and this drags them up to about 70% or so. Then when I get home at say 8pm and turn on the laptop and radio they plummet again. If I'm not near anyone I'll run the engine or the genny again to top up.

 

But the thing is, it is becoming clear to me that even if I got a Big Fat set of batteries that will last me all week and a Big Fat charger to fill them up again at the weekend, the charging properly to 90% might typically take about 10 hours, but to get to the 100% needed might take 20 hours.

 

Yes a 40 Amp 24v charger will stuff 60% of the charge back in over two or three in the bulk charge phase but it seems once the battery voltage rises to 14.8v and absorption charging is reached, charging to the point where the tail current falls to the nominal 1% cannot be hurried. It simply takes a flippin' long time. And I just don't spend enough time on the boat during the hours of 8am to 8pm to get those charging hours in. And nor would want to spend the whole of my weekends on the boat with the genny running if I'm not cruising.

 

I use a bit more than you, about 35ah at 24 volts. I need to run the engine between 3 and 4 hrs a day to see a charge current of 2 amps or just below at 29. something volts. I have 4 X 105 Tojans in series.

[MtB]

I use a bit more than you, about 35ah at 24 volts. I need to run the engine between 3 and 4 hrs a day to see a charge current of 2 amps or just below at 29. something volts. I have 4 X 105 Tojans in series.

 

Hmmm that would be completely untenable for me, being out and about for 10 hours of the day...

 

I'd like to charge for about an hour each weekend. That would be ideal.

But even so, thanks for the close comparison!

[Dalslandia]

When I had the boat on the ship yeard last winter, the staff there managed to left the light in the genset room on, and had disconnected the 24v battery charger that was on, I only have 2+2 starter batteries for main and genset, and have an interconnection between them as emergency jump cables. that interconnection was live, so i could charge all four batteries with one charger at low setting. gave the result that all four was flat, I thought I had to buy new, but had just bought a 12v CTEK 8 stage, up to 160 AH I think it said. for my car and other batteries, but decided to see if it was possible to get life in this on the boat, so I disconnected them and charged one and one, it have one recovery mode, so used that, and they took charge and worked just fine all summer, and even now in the cold they start up the engines with no problem.

CTEK also have 24V chargers they are a bit more pricy, the 12 V was som £50 i think.

Edited January 14, 2016 by Dalslandia

[MtB]

Oh but hang on, I'm using 25Ah at 12v. I have a 24v starter and alternator so have to have my domestic batteries at 24v too. But my power audit was for 12v appliances. I have a 24v to 12v dc step-down box of tricks.

[Dalslandia]

Oh but hang on, I'm using 25Ah at 12v. I have a 24v starter and alternator so have to have my domestic batteries at 24v too. But my power audit was for 12v appliances. I have a 24v to 12v dc step-down box of tricks.

 

25 Ah at 12v is some 300 Wh

300 Wh and an efficiency of 50% you need some 600 Wh to charge 20-25Ah at 24-29V

 

Q, is the 24/12 converter stealing your amp hours when you don't see?

I think you can save your batteries with a good charger,

Living in Sweden it is hard to believe there isn't a electric socket close to everywhere on land.

 

this is what i have (somewhere?)

http://www.ctek.com/se/sv/chargers/CT5%20TIME%20TO%20GO

 

24v chargers

http://www.ctek.com/se/sv/chargers/24v

​

Ps, a friend connected the battery charger to the 230 inverter in his boat, the inverter was fed by the batteries he was charging with the battery charger, well ... ds

Edited January 14, 2016 by Dalslandia

[cuthound]

Sounds like you need a winter mooring with a landline :)

[WotEver]

Hmmm that would be completely untenable for me, being out and about for 10 hours of the day...!

Each day, remove the batteries, place them in the back of your van, wire them in parallel to the vehicle battery. Leave the van ticking over for most of the day...

 

You might wish to continue ignoring me ?

[WotEver]

 

25 Ah at 12v is some 300 Wh

300 Wh and an efficiency of 50% you need some 600 Wh to charge 20-25Ah at 24-29V

Hmmm... another way to look at it is 25Ah @ 12V is 12.5Ah @ 24V. Assuming 80% efficiency of the 24-12 converter that increases the consumption to 15.6Ah = 28% DoD on as-new capacity. 15.8Ah isn't a lot but it requires more time than Mike has.

[Dalslandia]

Hmmm... another way to look at it is 25Ah @ 12V is 12.5Ah @ 24V. Assuming 80% efficiency of the 24-12 converter that increases the consumption to 15.6Ah = 28% DoD on as-new capacity. 15.8Ah isn't a lot but it requires more time than Mike has.

 

right, then the charging efficiency is some 50% I wrote a paper on that, have to check.

brb.

 

at SOC 70% efficiency should be 73%

and SOC 50% efficiency 67%

and SOC 20% Efficiency 50%

 

So it should Boil down to 73% efficiency

This is in-out efficiency, but I don't remember the discharge rate

 

= need some 22Ah input if his batteries was up to the job

​

Edited January 14, 2016 by Dalslandia

[nicknorman]

 

right, then the charging efficiency is some 50% I wrote a paper on that, have to check.

brb.

Charge efficiency of lead acid batteries is in the low to mid 90s%. Ours are currently on 94%

[WotEver]

Charge efficiency of lead acid batteries is in the low to mid 90s%. Ours are currently on 94%

Well, it's inversely proportional to SoC and might well drop to close to 50% at say 5%DoD but yes, as an average figure 90% is much closer than 50%.

 

right, then the charging efficiency is some 50% I wrote a paper on that, have to check.

brb.

 

at SOC 70% efficiency should be 73%

and SOC 50% efficiency 67%

and SOC 20% Efficiency 50%

 

So it should Boil down to 73% efficiency

​

Nope, should be a lot better than that. Trojan spec the T105 CE as 94%.

By way of example.

[Dalslandia]

Well, it's inversely proportional to SoC and might well drop to close to 50% at say 5%DoD but yes, as an average figure 90% is much closer than 50%.

 

Nope, should be a lot better than that. Trojan spec the T105 CE as 94%.

By way of example.

 

I think it was for a high discharge rate for a electric drive, make sense with higher eff. with lower discharge rate.

The Odessey batt 1800. have a 214ah 20h rating, and 190ah on 5 h rating

[nicknorman]

Well, it's inversely proportional to SoC and might well drop to close to 50% at say 5%DoD but yes, as an average figure 90% is much closer than 50%.

 

Nope, should be a lot better than that. Trojan spec the T105 CE as 94%. By way of example.

Yes fair enough. The electrons are only lost due to gassing and that occurs mostly near the end of the charge. Overall our Trojans are giving 93 to 94% on the Mastershunt with typical charges from 60-something % SoC

I think it was for a high discharge rate for a electric drive, make sense with higher eff. with lower discharge rate.

The Odessey batt 1800. have a 214ah 20h rating, and 190ah on 5 h rating

Don't forget there's a big difference between charge efficiency (amp hours out and in) vs power efficiency (watt hours out and in). The latter is always a lot worse due to high charge voltage and low discharge voltage.