Counting down amps

[Duchess Omnium]

On another thread Firesprite wrote:

 

 

What you take out of the batteries you have to put back 120%. ( If use 50 amps overnight you need to replace with 60amps)

 

Firesprite

 

In the office

 

Okay, I am still struggling with this 5 years on. I have a Link 10 battery monitor and a Sterling Alternator to Battery Charger, but I am still not sure I know how many amps I have used overnight...

 

The Link 10 tells me current volts (obviously different depending on whether engine on or off; it's usually down around 12.4 in the morning; when I charge in the evening it is usually around 12.10, never lower than 11.95 -- does this sound reasonable?). When I first turn the engine off it is around 12.8, but drops fairly rapidly. I know I don't ever get a stable reading because I keep the fridge on.

 

When I am running the engine the Amps reading on the Sterling and the Link 10 counts down. It is usually at around 1 or 2 on the Link and 7 or 8 on the Stering when I turn the engine off.

 

The SterlIng doesn't tell me what I have used, but the Link 10 does, so my theory was that I should replace the amp hours I have used, but as the number approaches zero it takes longer and longer to replace, so I am not sure that is the right measure. Every day I am a little below the minus amp hours that I was the day before until I have a cruise day or run the engine for four or five hours.

 

Meanwhile the Sterling thingy counts down amps usually starting around 50ish, sometimes up to about 70. The man at SterlIng told me that I would be wasting my money if I kept running the engine below about 20 amps, but I worry about the info t he Link 10 is giving me so I usually compromise on turning off at around 8 amps.

 

I end up running the engine for 2- 3 hours per day. Am I running it too much, or not enough? I think I am a pretty low power user, but it is hard to know.

 

Any advice?

[Neil TNC]

On another thread Firesprite wrote:

 

 

 

Okay, I am still struggling with this 5 years on. I have a Link 10 battery monitor and a Sterling Alternator to Battery Charger, but I am still not sure I know how many amps I have used overnight...

 

The Link 10 tells me current volts (obviously different depending on whether engine on or off; it's usually down around 12.4 in the morning; when I charge in the evening it is usually around 12.10, never lower than 11.95 -- does this sound reasonable?). When I first turn the engine off it is around 12.8, but drops fairly rapidly. I know I don't ever get a stable reading because I keep the fridge on.

 

When I am running the engine the Amps reading on the Sterling and the Link 10 counts down. It is usually at around 1 or 2 on the Link and 7 or 8 on the Stering when I turn the engine off.

 

The SterlIng doesn't tell me what I have used, but the Link 10 does, so my theory was that I should replace the amp hours I have used, but as the number approaches zero it takes longer and longer to replace, so I am not sure that is the right measure. Every day I am a little below the minus amp hours that I was the day before until I have a cruise day or run the engine for four or five hours.

 

Meanwhile the Sterling thingy counts down amps usually starting around 50ish, sometimes up to about 70. The man at SterlIng told me that I would be wasting my money if I kept running the engine below about 20 amps, but I worry about the info t he Link 10 is giving me so I usually compromise on turning off at around 8 amps.

 

I end up running the engine for 2- 3 hours per day. Am I running it too much, or not enough? I think I am a pretty low power user, but it is hard to know.

 

Any advice?

 

Just get a Smartgauge...you know it makes sense!

[Bob18]

Batteries are far from 100% efficient, and need to be returned to their full state of charge as soon as possible after discharge, so if you draw 50AHr from the battery at night you need to replace that 20Ahr, plus an amount that is determined by the battery type, and this could be as much as another 20Ahr.

 

You are UNDER charging your batteries.

 

By repeated UNDER charging a battery, as you are doing by only charging until the charge system is reading 20A you will shorten the battery life. You are heading in the right direction by going to 8amps, but even then you are not reaching full charge. You need to get to the point where the charge current has stabilised at near zero, and the voltage is at the float voltage for the battery type in use. You need to be getting the battery voltage up to between 13.2 and 13.8, and holding it there for some time to get the battery fully charged. Your 4-5 hour cruise is possibly making up for some of the under charging, but even that is a bit of a debate.

[ditchcrawler]

On another thread Firesprite wrote:

 

 

 

Okay, I am still struggling with this 5 years on. I have a Link 10 battery monitor and a Sterling Alternator to Battery Charger, but I am still not sure I know how many amps I have used overnight...

 

The Link 10 tells me current volts (obviously different depending on whether engine on or off; it's usually down around 12.4 in the morning; when I charge in the evening it is usually around 12.10, never lower than 11.95 -- does this sound reasonable?). When I first turn the engine off it is around 12.8, but drops fairly rapidly. I know I don't ever get a stable reading because I keep the fridge on.

 

When I am running the engine the Amps reading on the Sterling and the Link 10 counts down. It is usually at around 1 or 2 on the Link and 7 or 8 on the Stering when I turn the engine off.

 

The SterlIng doesn't tell me what I have used, but the Link 10 does, so my theory was that I should replace the amp hours I have used, but as the number approaches zero it takes longer and longer to replace, so I am not sure that is the right measure. Every day I am a little below the minus amp hours that I was the day before until I have a cruise day or run the engine for four or five hours.

 

Meanwhile the Sterling thingy counts down amps usually starting around 50ish, sometimes up to about 70. The man at SterlIng told me that I would be wasting my money if I kept running the engine below about 20 amps, but I worry about the info t he Link 10 is giving me so I usually compromise on turning off at around 8 amps.

 

I end up running the engine for 2- 3 hours per day. Am I running it too much, or not enough? I think I am a pretty low power user, but it is hard to know.

 

Any advice?

What Neil said plus if you are going down to below 12 volts off load you are going to low and if you then recharge for 3 hours you all most certainly are not fully recharging your batteries.

[Duchess Omnium]

i don't go below 12 off load... but I was worried I might be under charging. How many hours do most people charge?

 

Batteries are far from 100% efficient, and need to be returned to their full state of charge as soon as possible after discharge, so if you draw 50AHr from the battery at night you need to replace that 20Ahr, plus an amount that is determined by the battery type, and this could be as much as another 20Ahr.

 

You are UNDER charging your batteries.

 

By repeated UNDER charging a battery, as you are doing by only charging until the charge system is reading 20A you will shorten the battery life. You are heading in the right direction by going to 8amps, but even then you are not reaching full charge. You need to get to the point where the charge current has stabilised at near zero, and the voltage is at the float voltage for the battery type in use. You need to be getting the battery voltage up to between 13.2 and 13.8, and holding it there for some time to get the battery fully charged. Your 4-5 hour cruise is possibly making up for some of the under charging, but even that is a bit of a debate.

[blackrose]

i don't go below 12 off load... but I was worried I might be under charging. How many hours do most people charge?

 

That depends on what size domestic battery bank they have, how many amp hours they have used, and the output of their alternator or battery charger.

 

When Im away from my mooring I use a gas fridge, led lights and a small flat screen TV that only draws 1 amp. So if I want I can moor somewhere for 4 or 5 days before I need to recharge the batteries - but I always try to recharge them fully.

 

From say 60% charge left in the batteries I'd probably be looking at about 5 hours of recharging.

Edited October 29, 2011 by blackrose

[mrsmelly]

Just get a Smartgauge...you know it makes sense!

 

The only trouble with a SG is it tells you state of charge and nowt else. Its great to know that but my victron thingy as with others tells you what charge is coming in/out at any time what bit of kit uses what and you can watch the charging ampage drop as the charging goes on and see when it drops down to say throwing 4/5 amps into a 400/500 amp battery bank that the batterys are charged and that can be checked by the charging boosting system being on float. As a liveaboard of many years I have never needed a SG and my batteries last as long as anyone elses. So YES a SG is a good bit of kit but NO its is a very far cry from the only bit of kit on the market. I think even GIBBO would agree with that as I believe the new version of the SG is to have other such features.

[Keeping Up]

It's generally reckoned that the battery is reasonably well charged when the charge current in amps, at an applied voltage of typically 14.2v to 14.4v, has reduced to no more than 2% of the battery's amp-hour capacity. This means that you should recharge a single good 110 Ah battery until the current has fallen to less than 2.2 amps; if you have a bank of 4 batteries you are OK if you get the total charge current down to 8.8 amps.

 

If the batteries are a bit old, so their capacity is less, it is their reduced capacity that you should use in this calculation. So one old battery that has lost half of its capacity should be charged until the current has dropped to about 1 Amp.

 

Personally I reckon this still represents under-charging if that is all you do. During the summer I reckon to recharge to at least this level every day, and also to continue for no less than a couple of hours extra on at least one day in three - and even on that regime I have had problems this summer which my battery supplier is still actively investigating because my latest set of new batteries are acting as if they have been under-charged.

 

Charging by 2 or 3 hours a day is almost certainly not enough. There's an old saying that "it's time, not amps, that recharges a battery" and you can't get around that.

[Bob18]

You've got some monitoring equipment on board, use it to work out how many hours you need.

 

First, when charging you worry about VOLTAGES more than CURRENT, keep an eye on the current by all means, but look at the voltages. The current will start off high, and drop progressively toward zero, it will normally never quite reach zero as there is a lot of "interesting" stuff going on when you reach this level of charge....

 

 

You need to be bringing the standing voltage up to 13.8V, measured about two minutes after you stop charging and with no load the battery.

After a few hours, again with no loads on the battery, the voltage should drop to no lower than 12.6V, anything below this after the rest period indicates either an inadequately charged battery, or a battery that is on its way out.

 

 

 

Your measured voltages are certainly low, anything below 12.2v on a regular basis is "living on borrowed time" and 11.95 is heading into the danger zone.

 

Your charging voltage should be in the range 14.2-14.5V, be careful as the battery may start to "gas" if the charging voltage is held above 14.4V, how much gassing is very dependant on the exact state of the battery and its construction.

 

 

First give your battery a really good charge, from the sound of it you are looking at 6-8 hours needed.

Do a set of measurements (ever needed an excuse to got to the pub - two hours sounds like a lunchtime/evening visit...)

After a day's normal use and charge repeat the measurements and compare with those from the long charge.

[by'eck]

As well as advice above at least once measure under normal load the voltage at the battery(s) terminals using the best digital voltmeter you can buy/beg/borrow. This will give you an indication of how accurate your built-in voltage measuring equipment is. Inaccuracies will probably vary with load, but at least you can make informed allowances.

Edited October 29, 2011 by richardhula

[Bob18]

Thanks Richard,

I left the door open for you, and you accepted the (unwritten) invitation

[Chalky]

Exactly as Bob says. I usually start a recharge when the meter indicates 12.4v. The alternator supplies about 45A for about 1/2 hour as the voltage starts to creep up towards 14v. It can take an hour or two to reach this (depending how low I've let the batteries get). If I'm doing a quick charge I wait until I'm seeing 14.2v and about 6A ish. This can take 3/4 hours. A full charge can occur after 8 hours cruising. I'd expect to see 14.4V and about 2A.

If I'm standing for a couple of days I'll try to recharge when the batteries reach 12.6V. To reach 14.2V can take about 2 hours.

 

I had a problem with a pump being left on which let the batteries get down to 12.2V. From 12.2V it took 9 hours to get them up to 14.2V.

 

The first part of the charge is usually quite fast and is the bulk charge - this is when the alternator produces high currents and puts about 80% of the charge into the battery. It's about 20% of the charge time (crudely). The remaining 20% of the charge, the adsorption charge takes the remaining 80% of the time - the batteries are just slow in accepting it.

 

Open circuit my batteries are usually about 12.8v when fully charged. I have a small 5w solar panel to help overcome self discharge and this usually keeps them at about 13.2v ish.

 

Bob refers to something known as surface charge. This is down to the way battery chemistry works and means that straight after charging the battery voltage will appear higher than it will after a few hours. Think of it like the head on a beer - it'll disappear after a while and show the true battery voltage. You can remove the surface charge by turning a light on for a few minutes - this will have the same effect as leaving it for a while.

Edited October 29, 2011 by Chalky

[Bob18]

I like that beer analogy - very good and very understandable.

(Trouble is I never let my beers go flat...)

[Bimbly1]

You've got some monitoring equipment on board, use it to work out how many hours you need.

 

So where does the specific gravity come in all this? My four x135Ah batts seem to hold their charge but from new, when fully charged the SG has never been better that 1230 when I expected at least 1250.

[Bob18]

That sounds low 1250 is ideal fully charged, but depends to an extent on the particular battery.

[Theo]

Just get a Smartgauge...you know it makes sense!

 

Hear hear!

 

N

[Chalky]

I like that beer analogy - very good and very understandable.

(Trouble is I never let my beers go flat...)

 

I was thinking of the target audience!

Edited October 29, 2011 by Chalky

[tosher]

So where does the specific gravity come in all this? My four x135Ah batts seem to hold their charge but from new, when fully charged the SG has never been better that 1230 when I expected at least 1250.

 

Are your batteries "Elecsol" - these have a lower sg than normal open lead acid types.

[Duchess Omnium]

Hi, Folks, many thanks for these really helpful replies. I'll work through these ideas over a few days and come back with some more numbers, if I can and maybe ask for more help. Sounds like I have been concentrating on the wrong thing -- I watch the amp hours (typically I use 20-30 per day) and I watch the amps counting down. The Sterling guy said no point in carrying on when it gets below 20, but it sounds like you guys don't agree. Anyway, I usually give up when the Sterling monitor says around 8 (at that point the other monitor usually says about 2).

 

I know that as the batteries g et closer and closer to charge, it takes longer and longer, so I usually don't go below 8-10 amps, and I usually don't get the minus amp hours down to zero unless I cruise.

 

I have a domestic bank of 5 (110 amp) batteries, plus a starter battery and a 90 amp alternator + a 70 amp alternator. The Sterling charger links the two alternators and "boosts" them. This evening the volt meter read 12.3 when I turned the engine on (that's typical). Right now at 129 minutes on the Sterling is reading 7 amps and the "float" light is on, meaning, according to the instructions that the batteries are fully charged so the boost has been turned off. The volt meter on the other monitor (Link 10) says 14.5 volts, .1 amps and -12.5 amp hours. Yesterday I charged to -11.5 amp hours, so according to that I have replaced one less amp hour than I have used (?)

 

I live on the boat and run a fridge 24/7 so it is difficult to to get an accurate off load reading. The batteries are nearly new (installed in May). But I am getting so paranoid about this that I live in near darkness... I only watch (12 volt) tele for 1.5 hours on Sat and Sun eves, and then usually with the engine on. Lately I only wash dishes when the engine is on, only run the inverter when the engine is on, and hardly ever shower... (so if I don't stop worrying I will only have internet friends...). Maybe I need to buy a gennie?

[Chalky]

You're focusing on the amp hours when charging. Forget that. Look at the voltage and the current. Your alternator will regulate at something around 14.2 or 14.4v (It says 14.5 in your text). When you get to the regulator voltage (14.4 in my case) and the current drops to a couple of amps then they're fully charged - nothing to do with amp hours.

Edited October 29, 2011 by Chalky

[ditchcrawler]

You're focusing on the amp hours when charging. Forget that. Look at the voltage and the current. Your alternator will regulate at something around 14.2 or 14.4v (It says 14.5 in your text). When you get to the regulator voltage (14.4 in my case) and the current drops to a couple of amps then they're fully charged - nothing to do with amp hours.

No it wont because its going into a Sterling thingy

[Duchess Omnium]

oh dear.

[Bob18]

Ignore the ammeter for now, its not helping you get you batteries properly charged, an accurate volt meter is far more informative.

 

Assuming the engine was still running when you saw the 14.5V on the Link10 that's the output voltage from the alternator controller, and is about right to get a decent charge into the batteries provided you give enough time.

 

If you are constantly running at -11.5Ahr you will kill the batteries much quicker than properly charging them. With your Stirling alternator controller you need to run in float charge for several hours to fully charge the batteries, not just shut off as soon as you get into float - in "proper" float charging I'd only expect to see about 1 or 2 amp on your battery, not the 7 or 8 you are seeing.

 

It will not hurt the contents (provided it is cold to start with and not opened during that time) to stop the fridge for an hour or two so you have a chance to do a controlled charge/stand cycle.

 

There is a less accurate way to give you a rough idea of the state of the batteries:

Charge the batteries for several hours. About an hour before stopping the engine turn the fridge OFF. Stop the engine quickly measure thee battery voltage then turn ONE of the cabin lights(*) on for a two or three minutes, measure the battery voltage. If the battery is in good condition, and fully charged the first voltage should be very close to 14.5V, the second should be about 14V, wait another couple of minutes, and measure the voltage again, it should be about 13.8V. Turn the fridge back on. If the voltages are much lower then you have to continue charging for another couple of hours at least.

 

 

This sort of testing is just what weekends are for...

 

(*) I'm assuming your cabin lights have "ordinary" filament or halogen bulbs rated at about 20W.

[NB Willawaw]

Just out of interest, have you got the Sterling A-B Charger set for the right battery type ?

[mrsmelly]

Hi, Folks, many thanks for these really helpful replies. I'll work through these ideas over a few days and come back with some more numbers, if I can and maybe ask for more help. Sounds like I have been concentrating on the wrong thing -- I watch the amp hours (typically I use 20-30 per day) and I watch the amps counting down. The Sterling guy said no point in carrying on when it gets below 20, but it sounds like you guys don't agree. Anyway, I usually give up when the Sterling monitor says around 8 (at that point the other monitor usually says about 2).

 

I know that as the batteries g et closer and closer to charge, it takes longer and longer, so I usually don't go below 8-10 amps, and I usually don't get the minus amp hours down to zero unless I cruise.

 

I have a domestic bank of 5 (110 amp) batteries, plus a starter battery and a 90 amp alternator + a 70 amp alternator. The Sterling charger links the two alternators and "boosts" them. This evening the volt meter read 12.3 when I turned the engine on (that's typical). Right now at 129 minutes on the Sterling is reading 7 amps and the "float" light is on, meaning, according to the instructions that the batteries are fully charged so the boost has been turned off. The volt meter on the other monitor (Link 10) says 14.5 volts, .1 amps and -12.5 amp hours. Yesterday I charged to -11.5 amp hours, so according to that I have replaced one less amp hour than I have used (?)

 

I live on the boat and run a fridge 24/7 so it is difficult to to get an accurate off load reading. The batteries are nearly new (installed in May). But I am getting so paranoid about this that I live in near darkness... I only watch (12 volt) tele for 1.5 hours on Sat and Sun eves, and then usually with the engine on. Lately I only wash dishes when the engine is on, only run the inverter when the engine is on, and hardly ever shower... (so if I don't stop worrying I will only have internet friends...). Maybe I need to buy a gennie?

 

I think there is one small thing you need in the equasion. I too am liveaboard and decided years ago that life is too short to be spoilt by batteries. Yes indeed do as much as you can but dont let enjoyment of what you do be spoilt by a set of batteries. Hobby boaters do not knock hell out of their batts like we do so can spare the time and be battery anoraks if they want but as a liveaboard I am careful but I factor in a set of new batteries every year to eighteen months tops which is good and works out at not much more than ten bob a day.