Keeping batteries fully charged

[Kalapattar]

Hi! I have four 110a batteries and a 75amp alternator! Assuming I’m not using any power, how many hours does alternator need to keep them fully charged? Ta!

[Alan de Enfield]

To a certain degree the size of the alternator (after the 1st half an hour) is irellevant, the batteries control the charge rate, not the alternator.

 

It depends on how discharged they are.

 

Charging from 98% charged, probably a couple of hours to get to 100%

Charging from 50% charged, probably 8-10 hours to get to 100%

Charging from 25% charged, probably 12+ hours to get to 100%

 

The batteries are 100% charged when the tail charging current is 5 amps or less and the voltage has been at 14.6v for at least 1 hour.

Edited November 14, 2020 by Alan de Enfield

[Kalapattar]

Ok thanks! Gives me a guide!

[Chewbacka]

1 hour ago, Kalapattar said:

Hi! I have four 110a batteries and a 75amp alternator! Assuming I’m not using any power, how many hours does alternator need to keep them fully charged? Ta!

If you are leaving the boat unattended and there is no load on the batteries they will  self discharge, but at winter temps the rate from memory is a couple of percent per month.  So even in winter a solar panel will keep them full.

[Kalapattar]

Ok thanks! I do have a solar panel 120w but it’s not enough. A wind generator maybe?

[Tony Brooks]

Just now, Kalapattar said:

Ok thanks! I do have a solar panel 120w but it’s not enough. A wind generator maybe?

120w is more than enough when you are away from the boat so I assume you are a liveaboard. Wind generators tend to only produce a low percentage of their advertised output in inland locations. This is caused by low wind speeds and a lot of flukes in the wind caused by trees, the topography and buildings. My view is spend the money on more solar or a generator. Also do a power audit and match your use plus about 30% to what you can generate. For instance a metal type meat safe in the well deck will be almost as good as a fridge during the winter months.

[Sea Dog]

2 hours ago, Kalapattar said:

Hi! I have four 110a batteries and a 75amp alternator! Assuming I’m not using any power, how many hours does alternator need to keep them fully charged? Ta!

Even if you did know what percentage discharge you're starting at, it would be difficult to give a "when they're full by" time.

 

Do you have any way of monitoring the charging current that is flowing into your batteries? I have a similar sized battery bank and consider it full when I get a (tail current) reading dipping below 2 amps (others might quote something between 2-4% of capacity which is too high in my view, but essentially it's about when the steadily reducing charging current bottoms out). This is the most reliable guide for when to stop charging.

 

If you can't do that, you can use a voltmeter, fitted or a multimeter, to estimate state of charge but only after you've stopped charging.  Allow the batteries to rest after charging to let the surface charge dissipate and you'd expect to see at least 12.6v or a bit more for standard lead acid when fully charged. If you Google for a 12v battery state of charge chart (or some variation of that!) you'll be able to get an approximate % charge from that "resting voltage" reading.

 

Not really for working out when to stop charging, but it will at least give you an idea of where you are afterwards.  If you have a fitted voltmeter (or if you fit one - they're cheap) you can read this at a glance after they've sat overnight and use the chart to estimate where they as you start your day, which is perhaps a more useful way of using this info.

 

Try never to leave the boat with batteries in a less than fully charged state.  With everything switched off, they'd be fine left for a couple of months, but your solar will keep them there indeterminately even in winter.

[Kalapattar]

Ok thanks! I don’t understand why my solar isn’t enough. Someone once spoke about different  controllers. I’m using one supplied and is not faulty

[Alan de Enfield]

43 minutes ago, Sea Dog said:

If you Google for a 12v battery state of charge chart (or some variation of that!) you'll be able to get an approximate % charge from that "resting voltage" reading.

 

8 minutes ago, Kalapattar said:

Ok thanks! I don’t understand why my solar isn’t enough. Someone once spoke about different  controllers. I’m using one supplied and is not faulty

Solar doesn't work End October to March

 

Not enough Sun for enough hours per day.

If you have 1Kw+ of solar you may just get some useful charge in the Winter but it is not reliable.

 

What sort of controller do you have PWM or MPPT.

An MPPT is far more efficient and will give some 30% more charge than a PWM.

 

PWM are "£10's of pounds"

MPPT are in the £100's (depending on size - a 15 amp quality one is about £90)

https://www.photonicuniverse.com/en/catalog/full/369-Victron-BlueSolar-MPPT-7515-15A-solar-charge-controller-for-solar-panels-up-to-220W-12V--440W-24V-up-to-75V-.html?gclid=Cj0KCQiAnb79BRDgARIsAOVbhRqD3DtqILCT2_Dy84g3RthUoPFQEuaPzmR7Z7Qag5Od-icqcqMdeWYaAtBwEALw_wcB

 

A 50 amp quality MPPT is around £290

https://www.photonicuniverse.com/en/catalog/full/386-Victron-BlueSolar-MPPT-10050-50A-solar-charge-controller-for-solar-panels-up-to-700W-12V--1400W-24V-up-to-100V-.html?gclid=Cj0KCQiAnb79BRDgARIsAOVbhRqmF5Q6Ujp6qmQdKDTJMk61xCGHP3JHlFrzUfogj9TMfTNMgDwuSKoaAio0EALw_wcB

 

Like anything you can get a cheap Chinese MPPT off ebay for 'pennies' but it may not actually be an MPPT

You get what you pay for.

Edited November 14, 2020 by Alan de Enfield

[Tony Brooks]

21 minutes ago, Kalapattar said:

Ok thanks! I don’t understand why my solar isn’t enough. Someone once spoke about different  controllers. I’m using one supplied and is not faulty

I don't think that you have confirmed that you are a live aboard because as I said 120 watts of solar should be enough at this time of year. I got by with half that but not as a live aboard and that was with a PWM controller rather than an MPPT.

[Kalapattar]

Ok, I do live aboard and run my engine for at least two hours per day because solar panel doesn’t to the job apart from summer! 

[Kalapattar]

1 hour ago, Alan de Enfield said:

 

Solar doesn't work End October to March

 

Not enough Sun for enough hours per day.

If you have 1Kw+ of solar you may just get some useful charge in the Winter but it is not reliable.

 

What sort of controller do you have PWM or MPPT.

An MPPT is far more efficient and will give some 30% more charge than a PWM.

 

PWM are "£10's of pounds"

MPPT are in the £100's (depending on size - a 15 amp quality one is about £90)

https://www.photonicuniverse.com/en/catalog/full/369-Victron-BlueSolar-MPPT-7515-15A-solar-charge-controller-for-solar-panels-up-to-220W-12V--440W-24V-up-to-75V-.html?gclid=Cj0KCQiAnb79BRDgARIsAOVbhRqD3DtqILCT2_Dy84g3RthUoPFQEuaPzmR7Z7Qag5Od-icqcqMdeWYaAtBwEALw_wcB

 

A 50 amp quality MPPT is around £290

https://www.photonicuniverse.com/en/catalog/full/386-Victron-BlueSolar-MPPT-10050-50A-solar-charge-controller-for-solar-panels-up-to-700W-12V--1400W-24V-up-to-100V-.html?gclid=Cj0KCQiAnb79BRDgARIsAOVbhRqmF5Q6Ujp6qmQdKDTJMk61xCGHP3JHlFrzUfogj9TMfTNMgDwuSKoaAio0EALw_wcB

 

Like anything you can get a cheap Chinese MPPT off ebay for 'pennies' but it may not actually be an MPPT

You get what you pay for.

Thanks for your reply and info! It’s a MPPT controller but unsure what size it is! It was supplied with 120w panel

[Alan de Enfield]

6 minutes ago, Kalapattar said:

Ok, I do live aboard and run my engine for at least two hours per day because solar panel doesn’t to the job apart from summer! 

Thats about as I suggested, it depends how much you are using per day, you coupd be seriously undercharging your batteries and they could easily die within the next few weeks.

 

Have you undertaken a power audit ?

How does you consumption compare with your production ?

[Kalapattar]

I have no idea how to audit power. AVO,  calculations goes over my head

All I need is a cost saving easier way of preserving batteries, keeping them topped up rather than having to change them every couple of years

[Rob-M]

There isn't a short cut way to keep your batteries topped up.  What you use needs to be put back and putting it back takes time, you need to either run your engine for hours, use a generator, have a shore power connection with a mains charger or a roof full of solar panels.

[Dr Bob]

28 minutes ago, Kalapattar said:

I have no idea how to audit power. AVO,  calculations goes over my head

All I need is a cost saving easier way of preserving batteries, keeping them topped up rather than having to change them every couple of years

Buy yourself a battery monitor and learn how to use it. Siiiiimple.

[Alan de Enfield]

27 minutes ago, Kalapattar said:

I have no idea how to audit power. AVO,  calculations goes over my head

All I need is a cost saving easier way of preserving batteries, keeping them topped up rather than having to change them every couple of years

Unfortunately, living on a boat is unlike a house, you don't have un,limited services 'on tap' you have to actually 'work' at getting water, toilet emptied and power. You cannot keep taking power out without putting as much back in again, every time you do that you party sulphate the batteries and their capacity is lowered, the next time you don't fully recahrge, you get more sulpahation ad infiniyum until the battery becomes unusable.

 

If you are getting two years out of them and treating them badly then you are not doing badly.

What you need to remember is that batteries are disposable items and need replacing every couple of years (unless you learn how to look after them)

 

400Ah is only 4 batteries at £60 each.

£240 for 2 years life, or 33p a day. have one cup of coffee less per day and you get your batteries 'for free'.

3 minutes ago, Dr Bob said:

Buy yourself a battery monitor and learn how to use it. Siiiiimple.

But all that will do is tell him to charge them, he is loking for a cheaper way of keeping them partly charged and not having to replace them.

 

Recharging properly (when and by how much the monitor tells him) will cost more per week than his current system costs.

[LadyG]

10 hours ago, Kalapattar said:

Ok, I do live aboard and run my engine for at least two hours per day because solar panel doesn’t to the job apart from summer! 

Nor would it ever do so, I am liveaboard with a few hours of LED lighting and laptop ten hours, plus a phone, minimal usage.

I bought two panels of 275 watts each with an epever (chinese) controller and a Victron invertor 375watts from Bimble Solar, with cables etc. about £600, I paid labour , two days, using the previous solar rack, untilted.

 (sold the old 200 w with controller), so no extra holes in roof.

You can get second hand panels, cheaper, obviously, but the controller needs to be MPPT.

I look at the only LED voltage display I have (an imperfect system), check weather forecast and run engine accordingly, sun is due about ten thirty a.m., and will be energising for about five hours, so the engine is on now, it will run for one or two hours then off provided it is drawing less than 5 amps by then, yes it's not a perfect system, but it's the best I can do with my rather imperfect battery layout. I have nominal (guesstimate) 600ah battery capacity.

My winter battery management plan was to move boat once or twice per week to keep things on track , in theory I would have autonomy and well charged batteries. I would like a better monitoring of charge system, but it is what it is, if the three new  leisure batteries die after two years, it will be another £450, and a major kick in the goolies. This battery bank runs the water pumps and the Webasto and some lighting.

I replaced the starter battery this year with a 80ah, so only two more domestics to change, they are the hardest working batteries as they feed the invertor, all a bit higgeldy piggedy, but it seems to work. I live in hope,

Edited November 15, 2020 by LadyG

[RufusR]

Solar can be enough in winter if you have enough , but you need lots , we can charge to 100 percent most days but have 1630 watts , you have to think big if you want it to work , I am with Tony a back up generator is also a good idea for those odd ultra low light days but we only run it on average once every 2-3 weeks  dec jan and never other times , Wind seems fun and attracts me as s project one day but just for a hobbie rather than any expectation of it have a worth the money effect . 

 

Running engine Ines with alternator rarely gets batteries to a proper full state unless you are running it for ever , so alternate methods are preferable if living aboard . IMO most people don’t think big enough regard solar arrays on narrow boats hence disappointment when it does deliver in winter months . Solar panels are pretty cheap these days .  Roof space is an issue but can be overcome if creative thinking on a lot of boats 

[Tony Brooks]

17 minutes ago, RufusR said:

 IMO most people don’t think big enough regard solar arrays on narrow boats hence disappointment when it does deliver in winter months . Solar panels are pretty cheap these days .  Roof space is an issue but can be overcome if creative thinking on a lot of boats 

 

In my opinion also but doubt you could get enough on a narrrowboat for periods of winter if you still have a land based mind set and expect a floating cottage. This is why a power audit is vital so you know how to reduce your demand when you need to. Simply turning the fridge off during winter will save between 30 adn50 Ah per day, that is roughly equivalent to one typical battery. If you don't want to keep fresh food outside in winter cut a hole in the floor under a cupboard and keep the milk sitting on the base plate.

 

I find it rather disppoinmting that the OP says "I have no idea how to audit power. AVO,  calculations goes over my head. All I need is a cost saving easier way of preserving batteries, keeping them topped up rather than having to change them every couple of years". It is tantamount to saying "I can't be bothered to do any research so expect you lot to do it all for me even when I don't give you the information you would need to do so". Its not as if there are no examples of power/energy audits on the internet.

 

Basically the answer can only ever be:

 

A. reduce your consumption to the level at which you can fully recharge by whatever method.

B. increase your ability to recharge by some way that is practical and likely to work.

C. a combination of these.

 

Learning to use a simple ammeter and an accurate digital voltmeter to infer state of charge is probably the cheapest way of battery monitoring but that involves effort on the part of the user. Even with the majority of  all singing and dancing battery monitors will involve the user in a  good deal of study and learning if they want the best out of them.

 

For a start Mr @Kalapattar go onto my website and study the electrical course notes and also the   power/energy audit part of the maintenance notes. They will explain Amps, Volts and Ohms in terms you may better understand and also explain why you need so much apparent excess battery capacity and charging.

 

[LadyG]

Yes, I'm afraid being a liveaboard can be a bit of a struggle, I spent most of one day this week getting ten x25kg bags of coal on board, best part of one day last week shopping and buying diesel. Three times a week I have to top up with water, all due to current location which is ideal for isolation, but not for everything.  Shopping at Morissons was best part of a day, this week, though we have now agreed on 'special delivery for those needing a helping hand'.

PS sun has broken through cloud cover, engine drawing under 5 amps, turning it off in a few minutes. Peace, perfect peace.

I notice there is a fairly regular change in tone of the engine, I kinda assume this reflcts load, but I don't have anything which would cause that, not that I am aware.

PS it's now raining, quite hard, will leave engine running for another half hour, must try to get batteries ip to full charge at leat once a week.

Edited November 15, 2020 by LadyG

[Tony Brooks]

8 minutes ago, LadyG said:

I notice there is a fairly regular change in tone of the engine, I kinda assume this reflcts load, but I don't have anything which would cause that, not that I am aware.

 

Advercs will cause that as they cycle between low and high acceptance voltage - roughly every 15 to 20 minute cycles. The higher voltage causes more current flow so it loads the engine more. I don't know if other advanced alternator controllers do the same. I suppose under conditions where cloud cover varies solar output MIGHT cause the alternator to reduce its output and the increase it again as the clouds clear but that is just theorising and may be totally incorrect.

[blackrose]

11 hours ago, Dr Bob said:

Buy yourself a battery monitor and learn how to use it. Siiiiimple.

Yes, without being able to see and monitor what's going on you have no chance of managing it.

[blackrose]

11 hours ago, Kalapattar said:

I have no idea how to audit power. AVO,  calculations goes over my head

 

Then learn how do do it. It's really not that difficult. You're either interested in learning about this stuff or you're not.

 

https://notefromaboat.com/2018/12/15/how-to-do-a-power-audit/

[LadyG]

I don't think it is related to solar, it's doing it when it is raining and in 6/8 cloud, 

I'll have a look at the alternator and check it's data sheet, keeps me busy, or motivated, or something, anyway if it is an intentional function, it has to be a positive, my alternator is quite small, I think 70amps,  but 'if it ain't broke' .        

27 minutes ago, blackrose said:

Yes, without being able to see and monitor what's going on you have no chance of managing it.

Do these battery monitors need to be on each domestic battery bank, do they need me to do 'wiring'?

I am planning to replace my two (unknown type) bow batteries next year, easiest to replace similar footprint and orientation than with one monster, they are fairly difficult to access.

I think my ameter which is analogue, ie a dial gauge type is telling me what all the batteries are drawing, when I have all three isolator 'ON' Not sure what the analogue voltmeter is telling me,  but as long as it is over 13 and a bit once I turn the engine off, I think we are good to go, it doesn't seem to go any higher unless I have it connected to shorepower via the undersized and non regulated 20 amp charger, in which case it once went to 16, and the old Flooded lead acid batteries were bubbling!

Edited November 15, 2020 by LadyG