Charging of domestic batteries

[Alan de Enfield]

Interesting article (American, but a battery is a battery)

http://popupbackpacker.com/state-of-charge-your-camperrv-may-be-killing-your-battery-bank/

[Dr Bob]

22 minutes ago, cereal tiller said:

Not sure re the A to B Charger ,the Stirling Alternator Regulators Charge at full whack until 14 Volts then continue at 14.8 for one hour after the Timer is activated. restarting Engine will give the one hour  at 14.8 Volts again.

I'm not really sure how the AtoB works it out, but like you it seems to involve a timer. What is sure is that it goes to float too early and similar to the way the Victon multi goes to float (although I have not had much experience of that as we have not connected to shore power many times when down on SoC). An example of the AtoB is that if we are full after a days crusie, the following morning we will down by 80Ahr (ish). In the first hour of charging (when motoring) the voltage is over 14V (up to 14.5V) and the amps start at 70A and drop to 30A after the first hour. The amp hour counter shows typically 40Ahrs put back in and integrating a graph of amps v time in that first hour agrees. So we are now 40Ahrs off full charge. In the next hour the amps drop to 12A (2% of original capacity -660Ahrs) so integrating the Amps v time graph it looks like I have put in say another 15A hrs. At this point the BMV guage shows battery full, which is a lie - but that is down to my settings on the unit - still using the default values. We have therefore put in  55Ahrs of which maybe only 40Ahrs have been used to recharge the capacity - so we are 40Ahrs off full - but typically the AtoB has already switched to float mode and no more charging really takes place. Turn the engine off and on again and we get another hour of reasonable charge. Two hours running is just not good enough and 4-5 is really needed without solar (and a lot more if I was down to 50-60% SoC). I think the Sterling AtoB is switching to float as I am approaching a tail current of 2% (13A) but I just havent put enough current back in at that point to make up for what I used the night before. Not sure though if it is a timer or a reaction to a tail current. It seems to happen at the same time after starting the engine - but our current useage is pretty consistent.

I would like to understand a bit more about how these chargers (sterling, victron etc) decide when to go into float and if they can be optimised. Roll on March when the sun will work again!

[Tony Brooks]

1 hour ago, rowland al said:

Ran engine this morning after batteries down to about 12.1v from 12.45v. My old analogue ammeter showed (for the first time I can remember after tightening earth cable above) showed about 15a charging for the first 30 mins (after starter battery replenished). Seems to settle at about 10 amps instead of 1-2amps now. 

Obviously when I get my new digital meter I will be able to get more accurate measurements. 

Another question - is there an optimum charging plan when only using an engine and alternator to charge up the batteries (no shore line)? As it seems you could run the engine for hours just to get the batteries from 90% to near 100% capacity, is it more efficient on diesel just to stop at 90% (12.5v)?

15 amps is very low for those conditions. Are you sure you do not have a diode failure in the the alternator taking a phase or tow out?

In the conditioned described (as long as the ammeter is correctly connected) I would expect the alternator to deliver maximum output for a while. Even with an old alternator that would be 35 amps minimum.

If a diode or two have gone no enhanced battery charger can do anything to boost the charge.

[Dr Bob]

1 hour ago, rowland al said:

Although we do run the engine at times when moored just to charge the batteries (and get hot water), much of the time we are cruising when we are on the boat. So the batteries do get up to 12.6v on a regular basis.

 

As Alan says above, 12.6v is not enough but I am not sure if you are thinking 12.6v is fully charged. I use 12.72V as my 'full' voltage but you have to really be careful as it is useless to look at this if any solar is coming in. Also on our boat, we have an inverter running 24/7 so our 'at rest' voltage is really at -1.7A which depresses the voltage (and even more so in cold weather) so for you just aiming for 12.6V without understanding the other things going on is always going to end badly. For me 12.6V is 90% ish and too low.

[rowland al]

24 minutes ago, Dr Bob said:

As Alan says above, 12.6v is not enough but I am not sure if you are thinking 12.6v is fully charged. I use 12.72V as my 'full' voltage but you have to really be careful as it is useless to look at this if any solar is coming in. Also on our boat, we have an inverter running 24/7 so our 'at rest' voltage is really at -1.7A which depresses the voltage (and even more so in cold weather) so for you just aiming for 12.6V without understanding the other things going on is always going to end badly. For me 12.6V is 90% ish and too low.

I've never seen the Trojans more than 12.6v after they have settled down, even after 10 hours cruising. 

[rowland al]

40 minutes ago, Tony Brooks said:

15 amps is very low for those conditions. Are you sure you do not have a diode failure in the the alternator taking a phase or tow out?

In the conditioned described (as long as the ammeter is correctly connected) I would expect the alternator to deliver maximum output for a while. Even with an old alternator that would be 35 amps minimum.

If a diode or two have gone no enhanced battery charger can do anything to boost the charge.

Well it was reading about 30a for a few minutes longer than it used to before dropping to 15a. It's nearly 3 hours of engine running now an we're still charging at around 10a. So tightening up that earth connection has made a big difference. 

As the starter battery charges up very quickly and my domestics used to get from 12.1v to 12.5v in about 3 hours, I'm guessing the diodes are Ok. They might get charged up quicker now unless the dodgy connection only affected the ammeter reading.

[smileypete]

2 hours ago, rowland al said:

Another question - is there an optimum charging plan when only using an engine and alternator to charge up the batteries (no shore line)? As it seems you could run the engine for hours just to get the batteries from 90% to near 100% capacity, is it more efficient on diesel just to stop at 90% (12.5v)?

Doesn't have to be engine, could be genny & charger or solar.

Some even resort to using another battery! eg. splitting the bank bank so each half of the bank takes turns to get fully charged.

With engine or genny running it's a balancing act between fuel use and wear vs an acceptably small amount of cumulative capacity loss.

Edited November 14, 2017 by smileypete

[rowland al]

I took a few pictures of the rats nest. Not sure what you'll be able to make out though.

Edited November 14, 2017 by rowland al

[Alan de Enfield]

13 minutes ago, rowland al said:

I've never seen the Trojans more than 12.6v after they have settled down, even after 10 hours cruising. 

Maybe you need to have a word with Trojan as your figures are at odds with what they say

Trojan themselves say that your batteries (at 12.6v) are less than 90% SoC

 

Maybe it is time to just accept what you are being told.

[rowland al]

7 minutes ago, smileypete said:

Doesn't have to be engine, could be genny & charger or solar.

Some even resort to using another battery! eg. splitting the bank bank so each half of the bank takes turns to get fully charged.

With engine or genny running it's a balancing act between fuel use and wear vs an acceptably small amount of cumulative capacity loss.

Indeed. I suppose as we do a lot of cruising, we have never really seen a problem with the current regime. I only really kicked this thread off to try to understand what I was seeing with the ammeter. 

The good news is that the curiosity has paid off so far by finding that dodgy connection. It's also encouraged me to get a better meter. 

[Alan de Enfield]

Is that last pic (little black box) a Lucas Split charge relay ?

If so that'll be part of your problem and you will be losing around a volt from you charging system

[Tony Brooks]

The lower photo shows a split charge relay and as it has bolt on "main" connections it is better than it could be.

If the black cylindrical thing in the second from last photo is the ammeter then the wiring iis in my view the wrong colour and far to thin. It is probably causing voltdrop.

21 minutes ago, rowland al said:

Well it was reading about 30a for a few minutes longer than it used to before dropping to 15a. It's nearly 3 hours of engine running now an we're still charging at around 10a. So tightening up that earth connection has made a big difference. 

As the starter battery charges up very quickly and my domestics used to get from 12.1v to 12.5v in about 3 hours, I'm guessing the diodes are Ok. They might get charged up quicker now unless the dodgy connection only affected the ammeter reading.

Oh well, keep guessing, you might be correct but if its a 50 amp alternator or higher you may not be.

Edited November 14, 2017 by Tony Brooks

[rowland al]

2 minutes ago, Alan de Enfield said:

Maybe you need to have a word with Trojan as your figures are at odds with what they say

Trojan themselves say that your batteries (at 12.6v) are less than 90% SoC

 

Maybe it is time to just accept what you are being told.

A bit harsh, I was basing it on the table which seems to be banded around on here, It's also just possible that my Trojans are a bit knackered. 

Thanks for your input though. 

[Tony Brooks]

2 minutes ago, Alan de Enfield said:

Is that last pic (little black box) a Lucas Split charge relay ?

If so that'll be part of your problem and you will be losing around a volt from you charging system

What do you base that upon? Its not the silly one with 9mm blades. I have a similar Lucas split charge relay and it does not drop that much. Now its 10 years old maybe a few mA.

The cables look beefy enough for a modest alternator but as with the ammeter it all depends upon length.

I would be far more concerned about where the alternator B+ cable is connected.

[rowland al]

7 minutes ago, Tony Brooks said:

The lower photo shows a split charge relay and as it has bolt on "main" connections it is better than it could be.

If the black cylindrical thing in the second from last photo is the ammeter then the wiring iis in my view the wrong colour and far to thin. It is probably causing voltdrop.

h well, keep guessing, you might be correct but if its a 50 amp alternator or higher you may not be.

Ok, maybe best stop posting on this one for now until I get the digital ammeter. I'll see if I can borrow a portable scope to see if there is much ripple on the DC when charging. 

[nb Innisfree]

1 hour ago, Alan de Enfield said:

Interesting article (American, but a battery is a battery)

http://popupbackpacker.com/state-of-charge-your-camperrv-may-be-killing-your-battery-bank/

That link is a bit iffy, the author establishes SoC from a 'battery monitor', as we all know if it isn't a Smartgauge then SoC readings could be way out. 

[Dr Bob]

2 hours ago, rowland al said:

Ok, maybe best stop posting on this one for now until I get the digital ammeter. I'll see if I can borrow a portable scope to see if there is much ripple on the DC when charging. 

Your initial question was about charging Amps which seems to be related to a 'poor' meter (old, badly wired, etc, etc). The discussion has identified that you charge between 12.1V and 12.6V which has led a number of responders to say you are under charging/letting voltage go too low. Installing the ammeter will help understand the charging but a few questions on your set up in general so when you come back with ammeter readings, it is easier to diagnose.

- Voltage. How are you measuring it? Whilst ammeters dont have to be accurate, it is useful if a voltmeter can be at least 0.05V of the real value at 12.7V. I note in one post you do give a voltage to 2 decimal places so it sounds like you have a decent one, or is it similar to the ammeter? Its not a smartguage is it?

- Overall battery performance. You say this is your 3rd set in 5 years. I think you said you are CC'ing so perhaps not that bad - but only 225Ahrs? How do you do it? We use 80-85Ahrs each night and we are pretty frugal but more telly in the winter. With your set up at this time of year at that useage your trojans would be down to 50% each night (lower capacity at lower temps) and lower if there is any sulphation. I am sure they will get wrecked in a short period. Your initial question was not asking about battery management - just the charging issue - but the info you have given suggests there could be a better strategy. How many Amphrs do you typically use overnight? Forgot....you need a battery monitor for that.

- I dont think you have solar. If one thing you take away from this thread is that you need solar to make sure your batteries are healthy for 8 months of the year. It makes getting to 100% so much easier when the sun gets higher in the sky.

Edit...added the bit I was going to reply to...

If you can borrow a portable scope, can you not borrow a DC Amps clamp meter. Far more informative.

Edited November 14, 2017 by Dr Bob

[rowland al]

1 hour ago, Dr Bob said:

Your initial question was about charging Amps which seems to be related to a 'poor' meter (old, badly wired, etc, etc). The discussion has identified that you charge between 12.1V and 12.6V which has led a number of responders to say you are under charging/letting voltage go too low. Installing the ammeter will help understand the charging but a few questions on your set up in general so when you come back with ammeter readings, it is easier to diagnose.

- Voltage. How are you measuring it? Whilst ammeters dont have to be accurate, it is useful if a voltmeter can be at least 0.05V of the real value at 12.7V. I note in one post you do give a voltage to 2 decimal places so it sounds like you have a decent one, or is it similar to the ammeter? Its not a smartguage is it?

- Overall battery performance. You say this is your 3rd set in 5 years. I think you said you are CC'ing so perhaps not that bad - but only 225Ahrs? How do you do it? We use 80-85Ahrs each night and we are pretty frugal but more telly in the winter. With your set up at this time of year at that useage your trojans would be down to 50% each night (lower capacity at lower temps) and lower if there is any sulphation. I am sure they will get wrecked in a short period. Your initial question was not asking about battery management - just the charging issue - but the info you have given suggests there could be a better strategy. How many Amphrs do you typically use overnight? Forgot....you need a battery monitor for that.

- I dont think you have solar. If one thing you take away from this thread is that you need solar to make sure your batteries are healthy for 8 months of the year. It makes getting to 100% so much easier when the sun gets higher in the sky.

Edit...added the bit I was going to reply to...

If you can borrow a portable scope, can you not borrow a DC Amps clamp meter. Far more informative.

I can answer these now.

I measure voltage using a DVM at the battery terminals, and I have a LED voltmeter in the circuit not far from the battery which seems to back up what the DVM reads

The first set of 4 batteries came with the boat and I think they were 5-10 years old and were struggling. I suspected the second set  of 4 I bought had been previously used (acid around top of batteries and acid supplied in used containers), but they did the job for about 2 years.  I then decided to step down to a set of just 2 Trojans (which have been in for about 2 years now). 

We use a small 120w max inverter to drive a TV and Sat Rx (which I think take about 50w in total including the inefficiency of stepping up to 240v and back down again!). No washing machine and a gas fridge. I've just bought a 12v TV with sat built in, I believe this will reduce my TV useage to about 15w. Then just LED lights, water pump and shower evacuation pump.

Basically we can satisfy all our needs now without the small inverter (we have a generator if we ever need 240v).  So a wild calculation I'd say we will be using about 20Ah per night. Probably was double that with the less efficient TV arrangement. I don't believe I have ever run the voltage below 12.0v (looking at my LED voltmeter) on any evening and the 2 Trojans are still meeting our requirements after 2 years. 

Have thought about a solar panel and decided against it purely on the basis that everything seems Ok with our current amount of engine use. If we had a permanent mooring I'd jump at one like a shot. 

As I said, I'm fairly happy with the way forward. My main objective was to understand what I was seeing. It makes a lot of sense now, dodgy earth connection! 

I appreciate I could probably optimise things further but as the worst that can happen is to have to buy another set of 2 batteries  in a year or two, I'n beginning to think I can live with it. Solar panels, regulators, battery managers, premium batteries, all cost a lot of money after all! 

I will take some more accurate measurements later as it is good to know everything is working correctly and from an academic point of view it's interesting. 

Again, thanks to all those like yourself who have given me constructive advice. 

[WotEver]

5 hours ago, Dr Bob said:

... if we are full after a days crusie, the following morning we will down by 80Ahr (ish). In the first hour of charging (when motoring) the voltage is over 14V (up to 14.5V) and the amps start at 70A and drop to 30A after the first hour. The amp hour counter shows typically 40Ahrs put back in and integrating a graph of amps v time in that first hour agrees. So we are now 40Ahrs off full charge.

No you’re not because you haven’t taken into account Charge Efficiency. If you’ve put in 40Ah charge you’ve probably reduced the deficiency by around 33Ah. 

[WotEver]

1 hour ago, Dr Bob said:

How are you measuring it? Whilst ammeters dont have to be accurate, it is useful if a voltmeter can be at least 0.05V of the real value at 12.7V. I note in one post you do give a voltage to 2 decimal places so it sounds like you have a decent one, or is it similar to the ammeter? Its not a smartguage is it?

Other than having a resolution of only 1.5 decimal places why do you think that would be a problem?

[Gareth E]

I have a Trojan battery. At this time of the year I charge it with a genny through my Sterling battery charger, set at 14.8v. I'm now aware that in colder weather I should be charging at a higher voltage. I haven't fitted the temperature sensor supplied, it was too awkward to get it through the bulkhead to where the charger is.

Could someone suggest an ideal voltage for 10 degrees c?

Might an option be to dangle the temperature sensor out of a window whilst charging, let the charger do the calculations?

Also, if the charger does compensate for a lower temperature, am I right in thinking that the setting (14.8v) that shows on the box would change to the compensated figure, or does that go on in the background? 

[Dr Bob]

15 minutes ago, WotEver said:

No you’re not because you haven’t taken into account Charge Efficiency. If you’ve put in 40Ah charge you’ve probably reduced the deficiency by around 33Ah. 

If you read the next sentence of the post, you will see that I take the 40Ahrs plus the next 15Ahrs (=55Ahrs) and then because of charging loss that probably represents 40 Ahr only into the batteries - so covering what you say. You're right it is a very important point and just shows when you estimate what you are putting back in, how difficult it is to get to 100%.

11 minutes ago, WotEver said:

Other than having a resolution of only 1.5 decimal places why do you think that would be a problem?

TIC?

[MtB]

1 hour ago, WotEver said:

Other than having a resolution of only 1.5 decimal places why do you think that would be a problem?

 

That selective amnesia of yours really needs fixing!!

We know for a fact and so do you, that not all Smartgauges out there are correctly calib.... ...oh forget it... 

[rusty69]

15 minutes ago, Mike the Boilerman said:

 

That selective amnesia of yours really needs fixing!!

We know for a fact and so do you, that not all Smartgauges out there are correctly calib.... ...oh forget it... 

If your not happy with your SG x 2 I will give you a tenner for both.

[MtB]

3 minutes ago, rusty69 said:

If your not happy with your SG x 2 I will give you a tenner for both.

 

No thanks, I'm delighted with them both. Between them the tell me the state of charge of my batteries, roughly.

Very, very, verrrrry roughly...!