Battery Management

[Richard10002]

3 hours ago, Gareth E said:

I'm not sure about that but regular looks at the meter suggests voltage stays at 14.6 until amps drop to around 0.8. It then goes into float at 13.4v, amps then drop slowly over an hour or two until they settle at 0.4. This suggests to me that the tail current is the tail current, the voltage is irrelevant, other than perhaps it taking longer to get to the tail current at 13.4v than it does at 14.6.

See my #20

 

You say that it stays at 14.6V until the amps drop to 0.8, when it goes into float at 13.4V.

 

I think it's the other way round... when it goes into float at 13.4V, the Amps drop to 0.8.

 

Tail current of 1% to 2% suggests that batteries are fully charged at a voltage of around 14.4V and above. Measuring tail current at a voltage of 13.4V, or anything much less than 14.4V gives you no information, and relying on it will destroy your batteries, (possibly not in summer).

[Dr Bob]

I smile at all this talk of tail current. I find it very difficult to actually measure a tail current.

I have 5 sources of charging. All switch into float ahead of 1% charge current (7A for my 660Ahr bank). I have a Victron Combi, a victron IP22, a Sterling AtoB and two separate MPPT controllers for the solar. Each drops to float at the slightest excuse. Only the AtoB is controllable enough to force another round of 14.4V by turning the engine off and then starting again.... then you get another hour of 14.4V and you can see a 'tail' current...I think. The mains chargers dont stay in absorption long and if reset just go into float again.

Has anyone actually got a form of charging that holds a tail current at 1% constant for 15 mins without going to float without resetting?  I know Richard also complains about his Sterling mains charger switching to float too soon.

[Tony Brooks]

13 minutes ago, Dr Bob said:

I smile at all this talk of tail current. I find it very difficult to actually measure a tail current.

I have 5 sources of charging. All switch into float ahead of 1% charge current (7A for my 660Ahr bank). I have a Victron Combi, a victron IP22, a Sterling AtoB and two separate MPPT controllers for the solar. Each drops to float at the slightest excuse. Only the AtoB is controllable enough to force another round of 14.4V by turning the engine off and then starting again.... then you get another hour of 14.4V and you can see a 'tail' current...I think. The mains chargers dont stay in absorption long and if reset just go into float again.

Has anyone actually got a form of charging that holds a tail current at 1% constant for 15 mins without going to float without resetting?  I know Richard also complains about his Sterling mains charger switching to float too soon.

 

Ordinary basic alternator.

 

You are correct though that all the modern charging gizmos make measuring tail current difficult. I don't see why both solar and mains charger manufacturers can't have a button that puts the charger at above 14 volts for an hour before reverting to float.

 

[Robbo]

15 minutes ago, Dr Bob said:

I smile at all this talk of tail current. I find it very difficult to actually measure a tail current.

I have 5 sources of charging. All switch into float ahead of 1% charge current (7A for my 660Ahr bank). I have a Victron Combi, a victron IP22, a Sterling AtoB and two separate MPPT controllers for the solar. Each drops to float at the slightest excuse. Only the AtoB is controllable enough to force another round of 14.4V by turning the engine off and then starting again.... then you get another hour of 14.4V and you can see a 'tail' current...I think. The mains chargers dont stay in absorption long and if reset just go into float again.

Has anyone actually got a form of charging that holds a tail current at 1% constant for 15 mins without going to float without resetting?  I know Richard also complains about his Sterling mains charger switching to float too soon.

You may find the Combi has a max absorption time that you change as it may be hitting that limit.  

[Dr Bob]

5 minutes ago, Tony Brooks said:

 

Ordinary basic alternator.

 

 

Yes, of course. I do have one of them now on my engine start battery and it is always at 14.3 ish.....so that is 6 ways of charging.

5 minutes ago, Robbo said:

You may find the Combi has a max absorption time that you change as it may be hitting that limit.  

Maybe? I'm not using the combi to charge any more as Ive changed to use the IP22 but I seem to remember that when the combi went to float, if I switched it off and on again, it still dropped out of absorption very soon after. We wont be back on shore power for months so I cant check. You also assume I am clever enough to work out how to change the dip switches in the Combi. I am not even sure I want to take the front panel off! Good input though.

[Robbo]

9 minutes ago, Dr Bob said:

Yes, of course. I do have one of them now on my engine start battery and it is always at 14.3 ish.....so that is 6 ways of charging.

Maybe? I'm not using the combi to charge any more as Ive changed to use the IP22 but I seem to remember that when the combi went to float, if I switched it off and on again, it still dropped out of absorption very soon after. We wont be back on shore power for months so I cant check. You also assume I am clever enough to work out how to change the dip switches in the Combi. I am not even sure I want to take the front panel off! Good input though.

It may need the voltage settings changing as well if you’ve never configured it for your batteries.   The Victron (depending on age) can also be set for a fixed absorption time rather than adaptive.   This may be preferable if you were charging via generator.

[cuthound]

2 hours ago, Dr Bob said:

Has anyone actually got a form of charging that holds a tail current at 1% constant for 15 mins without going to float without resetting?  I know Richard also complains about his Sterling mains charger switching to float too soon.

 

Back in the 70's when charging telephone exchange batteries, the rectifiers (chargers) had manually adjustable output, adjusted every 15 minutes. We used to charge at a constant rate  (C10 IIRC) until the cells began to gas freely, then at 2.67 volts per cell until the tail current was constantly for 3 x 30 minute measurements.

[George and Dragon]

On 23/06/2018 at 08:21, Gareth E said:

Perhaps it varies with different batteries but the tail current with my single 105ah Trojan is 0.38%. I know this because the amp reader on the Tracer meter settles at 0.4 amps after many hours of hot sunshine, with everything turned off.

Oh dear - someone has introduced tail current into my idiot's guide thread. 

I was saving that for when I had more than a very basic understanding

[George and Dragon]

On 21/06/2018 at 09:26, Lily Rose said:

This was exactly my situation, and with exactly the same concern, when I bought my boat in August 2015. The following June I had 2 * 100W of solar fitted, although I now regret not having larger panels.

  

 These have pretty much removed the concern about mooring up for a few days, at least in late spring, summer and early autumn. At least if the weather is reasonable. If we moor up for a day or more due to continuous dark clouds and rain then, depending on voltage readings, I may have to bite the bullet and run the engine but our reasons for not moving are usually more to do with good weather and a good location and less to do with a full day of bad weather. Even in bad weather we normally try to move for a couple of hours if possible in preference to running the engine without moving.

Thank you. That's very reassuring. 

I guess my next step should be to try to find some way of capturing how much energy we're using. Then I'd have a chance of predicting how long I needed to run the engine to recover that charge.

The boat is now back on the marina and connected to the shoreline. Batt 1 was showing 13.8 V, batt 2 12.7 V which suggests to me that batt 2 wasn't drawing any current from the charger.

On 22/06/2018 at 17:01, PeterF said:

The biggest power draw on the washing machine is heating up cold water, not the motor turning the drum. I installed a washing machine on our boat over the winter and put a thermostatic mixer valve on the water supply, taking from both hot and cold feeds. I set this up for just over 30degC by filling some saucepans from the hose with a thermometer in and run 30degC washes. The heater is never called upon so we only ever see the inverter pulling 30 to 40 Amps for the motor.

That's a good idea. I wonder if I can retrofit one of those

[Tony Brooks]

I bet battery 1 is the start battery and will be fully charged within perhaps half an hour of starting. Battery 2 is probably the domestic battery and is drawing a lot of current. Its the current flow through the charger that is pulling the voltage down to 12.7V.

 

To me its battery 1 that is drawing the least current and may well be in float mode.

[George and Dragon]

10 minutes ago, Tony Brooks said:

I bet battery 1 is the start battery and will be fully charged within perhaps half an hour of starting. Battery 2 is probably the domestic battery and is drawing a lot of current. Its the current flow through the charger that is pulling the voltage down to 12.7V.

 

To me its battery 1 that is drawing the least current and may well be in float mode.

I think batt 1 is the starter. Those measurements were taken after we'd been on the shoreline overnight. You may remember I have previously mentioned that Batt 1 is at 12.5 V in the morning while we're cruising and I suspect it is on it's way out.

 

Is there a link to the the idiots' guide so I can understand float mode?

Edited June 24, 2018 by George and Dragon
missing

[Tony Brooks]

14 hours ago, George and Dragon said:

I think batt 1 is the starter. Those measurements were taken after we'd been on the shoreline overnight. You may remember I have previously mentioned that Batt 1 is at 12.5 V in the morning while we're cruising and I suspect it is on it's way out.

 

Is there a link to the the idiots' guide so I can understand float mode?

 

Here

 

The charging voltage from any source is set to provide the optimum recharge time. This typically requires a charging voltage with modern batteries of between 14.2 and 14.6 so the alternator's regulator is st to this sort of value. A higher voltage is likely to cause the batteries to gas, dry out and if prolonged suffer plate damage. That is fine for the alternator that rarely gets the batteries fully charged and even when it does soon get shut down.

 

You still want the optimum recharge time from solar or a battery charger so initially they are set to TRY (they wont succeed) to charge at a similar voltage. At first the batteries demand so much charging current it causes the charge source to operate at a reduced voltage that gradually rises as the batteries charge and the current they demand falls.

 

This is known as the BULK phase. That is the charge source delivering a high current at a reduced voltage.  Alternators also act like this.

 

 

As the current drops further the voltage continues to rise until it reaches a set voltage as described in the first paragraph. The voltage would continue to rise unless the charge source took steps to prevent battery damage so it does. It starts to regulate the charging voltage holding it at around the 14.4 volts. This varies from source to source and some may be adjustable.

 

This is known as the ABSORPTION phase.

 

 

Now if the charge source is left on for long periods so we are talking battery charger or solar that 14.4 volts (or whatever) would fully charge the batteries and then be too high and cause damage so to prevent this the charger or solar controller automatically drops its voltage to around the 13.5 volts that is just enough to keep up with the batteries self discharge but not enough to cause damage.

 

This is known as the FLOAT phase and unless some other form of damage is in the battery can be left at this perfectly safely.

 

 

However although its easy to give a human the rule to keep charging until the current is 1% of battery capacity at 14.4 volts it is expensive/difficult for a charger or solar controller to act like this so they tend to try to use "cleaver" algorithms involving time and voltage rise to decide when to go into float. Unfortunately they all too often get it wrong and reduce the voltage too soon.

 

 

 

So if you had a charger on overnight both banks should be be fully charged and bank 1 seems to be (in float voltage). bank 2 either has a heavy load connected when you took the reading or is still drawing a lot of current because 12.7 is a bit low for float I would have thought (but read the charger manual) and is too low for absorption. I think at least one cell in bank 2 has internal shorts.

[MtB]

15 hours ago, George and Dragon said:

Is there a link to the the idiots' guide so I can understand float mode?

 

 

The trouble is, although batteries initially appear simple this is actually a complex subject which cannot be simplified without leaving out large chunks of important information. A good proportion of boaters never grasp all the fundamentals. 

 

In addition to Tony's summary above, there is also a very well written explanation by WotEver here:

https://www.canalworld.net/forums/index.php?/topic/95003-battery-charging-primer/

 

For boaters who find it all to difficult to grasp, or who want to spend their time boating rather than poring over the details of how properly to look after batteries, the alternative is to just accept that batteries are a consumable item which need replacing every year or two when they get knackered.

 

Most of us here have knackered a set of batteries or two (or four) when learning how to look after them, even those who now understand the subject well.

 

[George and Dragon]

4 hours ago, Tony Brooks said:

 

Here

 

The charging voltage from any source is set to provide the optimum recharge time. This typically requires a charging voltage with modern batteries of between 14.2 and 14.6 so the alternator's regulator is st to this sort of value. A higher voltage is likely to cause the batteries to gas, dry out and if prolonged suffer plate damage. That is fine for the alternator that rarely gets the batteries fully charged and even when it does soon get shut down.

 

You still want the optimum recharge time from solar or a battery charger so initially they are set to TRY (they wont succeed) to charge at a similar voltage. At first the batteries demand so much charging current it causes the charge source to operate at a reduced voltage that gradually rises as the batteries charge and the current they demand falls.

 

This is known as the BULK phase. That is the charge source delivering a high current at a reduced voltage.  Alternators also act like this.

 

 

As the current drops further the voltage continues to rise until it reaches a set voltage as described in the first paragraph. The voltage would continue to rise unless the charge source took steps to prevent battery damage so it does. It starts to regulate the charging voltage holding it at around the 14.4 volts. This varies from source to source and some may be adjustable.

 

This is known as the ABSORPTION phase.

 

 

Now if the charge source is left on for long periods so we are talking battery charger or solar that 14.4 volts (or whatever) would fully charge the batteries and then be too high and cause damage so to prevent this the charger or solar controller automatically drops its voltage to around the 13.5 volts that is just enough to keep up with the batteries self discharge but not enough to cause damage.

 

This is known as the FLOAT phase and unless some other form of damage is in the battery can be left at this perfectly safely.

 

 

However although its easy to give a human the rule to keep charging until the current is 1% of battery capacity at 14.4 volts it is expensive/difficult for a charger or solar controller to act like this so they tend to try to use "cleaver" algorithms involving time and voltage rise to decide when to go into float. Unfortunately they all too often get it wrong and reduce the voltage too soon.

 

 

 

So if you had a charger on overnight both banks should be be fully charged and bank 1 seems to be (in float voltage). bank 2 either has a heavy load connected when you took the reading or is still drawing a lot of current because 12.7 is a bit low for float I would have thought (but read the charger manual) and is too low for absorption. I think at least one cell in bank 2 has internal shorts.

Thank you. Very helpful.

As these batteries were bought with the boat I don't have a full history. For the time being they seem to be adequate and holding sufficient charge for our needs. When that changes I will look again at the whole topic in some depth since there seem to be a number of expensive options and some very expensive. Perhaps there is another thread discussing the merits of Trojans, Rolls etc and the less expensive alternatives.

Also, I may look at LiFePO4s although they currently appear to be exceptionally expensive so unless they can tolerate deeper discharge and/or being left uncharged for extended periods of time I very much doubt they'll be the final choice.

[Tony Brooks]

LiFePO4s are very, very new. Please do not be tempted to be a guinea-pig user.

 

There is absolutely no point in buying expensive batteries until you are sure you can look after them properly e.g. Rolls, Trojan etc. If you do buy before you have a good grasp of batteries you will just be wasting money. Whilst I would not suggest you buy the cheapest I would suggest that you stick to wet open cell batteries for now because despite the theoretical advantages of AGM batteries its far, far easier for an ordinary boater to diagnose  wet open cell batteries with a hydrometer. There are endless threads discussing such batteries but its seems those most in favour are those who have spent money on them. Much depends upon how you use/abuse your batteries.

 

I bought Exide 115 Ah wet open cell batteries six years ago and although I too suspect they are well down on capacity now they still meet our needs so I too am not going to change them yet.  My solar or your mains charger will have a lot to do with maximising battery life.

 

Be very aware that the  number of years a battery is guaranteed for has nothing to do with expected life. It is a guarantee against manufacturing defect and the battery will usually be in the vendors hands when you are told there was no defect.

[George and Dragon]

1 hour ago, Tony Brooks said:

LiFePO4s are very, very new. Please do not be tempted to be a guinea-pig user.

Advice noted. Though, from reading Victron's material, it seems that keeping them below capacity extends their life.

1 hour ago, Tony Brooks said:

There is absolutely no point in buying expensive batteries until you are sure you can look after them properly e.g. Rolls, Trojan etc. If you do buy before you have a good grasp of batteries you will just be wasting money. Whilst I would not suggest you buy the cheapest I would suggest that you stick to wet open cell batteries for now because despite the theoretical advantages of AGM batteries its far, far easier for an ordinary boater to diagnose wet open cell batteries with a hydrometer. There are endless threads discussing such batteries but its seems those most in favour are those who have spent money on them. Much depends upon how you use/abuse your batteries.

Too early to tell. I shall certainly be keeping a bottle of de-ionised water on hand...

I've seen people mention digital hydrometers - is there any significant advantage to these?

 

[Robbo]

8 minutes ago, George and Dragon said:

Advice noted. Though, from reading Victron's material, it seems that keeping them below capacity extends their life.

LiFePO4 are probably the best battery technology out at the moment if your; off-grid all year round and a liveaboard.   As long as the installation is correct (ie, BMS, correct charging voltage), then they are the most cost effective for fit and forget batteries.   Traction batteries probably are more probably more cost effective if you can charge them daily (solar in summer and on shore in winter?) and look after them, but it may cost more than the LiFePO4's in diesel if that is your main charging source.   

[Tony Brooks]

4 minutes ago, George and Dragon said:

Advice noted. Though, from reading Victron's material, it seems that keeping them below capacity extends their life.

Too early to tell. I shall certainly be keeping a bottle of de-ionised water on hand...

I've seen people mention digital hydrometers - is there any significant advantage to these?

 

 

I think a refractometer is probably a better and more accurate instrument as long as you do not get battery acid on your cloths.

 

I have also looked at the price of a digital version and they seem to be made for professional use in places like battery back up power systems. Cost over $1000 to £5000 so I would hope they are good. Not spent much time on it though. As they must suck the acid up and discharge it themselves I would be wary about the life of cheaper models and the accuracy must be related to exactly how they convert the Sp. Gr. to a digital signal. I  can see a  cheap China special could simply use a float and variable resistor or shaft encoder and if so not that much more accurate than a refractometer and possibly less so.

 

Basically with Sp. Gr. you are comparing cells rather than trying to accurately measure the state of charge. I am firmly convinced that a £5.00 glass float type hydrometer is more than adequate for ordinary boaters and when its useful to use a hydrometer to assess the state of charge rather than rested voltage (which you should know form "early this morning" you will be comparing the state of charge from hydrometer against the rested voltage to assess the degree of sulphation present so again it does not have to be particularly accurate.

[Gareth E]

On ‎24‎/‎06‎/‎2018 at 11:33, Richard10002 said:

See my #20

 

You say that it stays at 14.6V until the amps drop to 0.8, when it goes into float at 13.4V.

 

I think it's the other way round... when it goes into float at 13.4V, the Amps drop to 0.8.

 

Tail current of 1% to 2% suggests that batteries are fully charged at a voltage of around 14.4V and above. Measuring tail current at a voltage of 13.4V, or anything much less than 14.4V gives you no information, and relying on it will destroy your batteries, (possibly not in summer).

Just to confirm: I have a Tracer 30a controller with the added meter, running off 3 x 125w panels.

 

My electrical usage is minimal (gas fridge, led lights, little use of telly). I've had this set up for 4 years. At first the readings were a bit baffling, as was everything to do with batteries, resulting in me destroying 2 sets in 2 years. I've a better grasp of it now, went down to a single Trojan battery (power use circa 30ah/ day)

 

Pretty well every day from March to October I wake up, assuming the sun isn't up, with volts showing either 12.6 or 12.7. If there's decent sun the meter will then show 5 or 6 amps going into the battery, with volts rising to around 14.8. Over 2 or 3 hours amps drop to 0.8-1 with volts still being around 14.8. Then, when amps are around .8 to 1 the voltage suddenly drops to 13.4- 13.6 while the amp reading remains the same. Then, over 2 or 3 hours, amps drop to 0.4. If I switch say the telly on amps will rise but volts won't. That's unless I'm using a heavy load e.g. angle grinder off the inverter. In this case, as the current from the panels is insufficient to power the device, power is being drawn from the batteries.

 

My understanding of all this is that the voltage drop to 13.4-13.6 signifies the controller going into float mode. It only goes out of float mode when a demand is made on my battery (angle grinder).

Edited June 25, 2018 by Gareth E