Battery Not Charging

[tommytelford]

Wondered if anybody can help. I have had trouble with my second battery not charging to it's full extent. I have replaced it with a new one but am having the same problem. Is it possible that the positive lead connecting the 2 batteries could be too small, the earth connection is connected to the 2nd battery which isn't charging fully

[Tony Brooks]

As so often!

 

What tells you it is not charging to its full extent?

 

Single or twin alternators (I think single is implied from the question)?

 

If single what type of charge splitting? If its a slit charge diode then you probably have the answer.

 

If a split charge diode is the alternator battery or machine sensed (I know that seems complicated but it needs considering, most are machine sensed unless a Sterling type gizmo has been added these days).

 

If not a split charge diode then how is the alternator and charge splitting device wired to the banks?

 

How thick are the charging cables? Comparison with pens, fingers etc. will do at this stage.

 

Then we will have a better idea of what to say.

[Tony Brooks]

Or, re-reading the original post as no clarification has been given do you mean that you have a battery bank of two batteries and one of them is not charging properly?

 

Even if this is what you meant we still need clarification.

 

If this is a split charging system with one engine battery and one domestic battery the two battery negatives should be joined by a large battery link cable. If its a single alternator boat the two positives will be joined at some time and in some way that allows them to be "unjoined" whenever the alternator stops charging. This "joining thing" could be a big rotary switch, a split charge diode system of a variety of types, or a split charge relay of some sort. In the case of a big switch the problem is most likely to be operator error, otherwise it is likely to be the "joining thing".

 

If you are just talking about one battery of a bank of two in parallel then I would like to see the evidence of "not charging properly" because in normal use and without testing you would not know. With a bank of two it could be a thin positive or negative interlink, dirty battery clamps/posts/connections, resistive crimps on terminals and so on but the most likely as long as the interlinks are thick enough is that you have the main positive and negative connections both on the same battery. However I doubt you would notice the difference this would make on a bank of just two batteries. All this assumes that you are not feeding anything from just one battery.

 

If you are talking about 2 batteries in series to give 12 or 24 volts in total then an undersized interlink cable should just compromise the charge to both batteries, not just one.

 

Once we can quantify what set-up you have and what the problem is we can give more directed advice. There are other things that might cause you to think that on certain set-ups like a faulty master switch but we need more information.

 

You may notice that none of our other electrical "experts" have replied to you. This is almost certainly because of lack of information.

[tommytelford]

I have 2 battery banks, the starter battery and two domestic batteries in parallel , the control is the big red knob type and the link cable is about the size of a pencil but the earth lead the size of a small finger. I have checked voltages on the changeover switch and they seem to be ok

[ditchcrawler]

I have 2 battery banks, the starter battery and two domestic batteries in parallel , the control is the big red knob type and the link cable is about the size of a pencil but the earth lead the size of a small finger. I have checked voltages on the changeover switch and they seem to be ok

is the big red thing a 1 2 both off switch?

[Tony Brooks]

I have 2 battery banks, the starter battery and two domestic batteries in parallel , the control is the big red knob type and the link cable is about the size of a pencil but the earth lead the size of a small finger. I have checked voltages on the changeover switch and they seem to be ok

 

Are you saying that one of your two domestic batteries stays less well charged than the other? If so first make sure ALL charging and feed to equipment leads have the positives on one battery and the negatives on the other.

 

About as thick as a pencil sounds very much like 120/0/20 cable with a conductor cross sectional area of 8.5mm. As the BSS as I recall requires 25 sq mm CSA which has an OD of about 9.8mm the boat should not have passed its BSS inspection. Yes the cable is too small but then again if you only have a 35 or 40 amp alternator and only lighting loads it should not cause your symptoms.

 

For the sake of the BSS get the cable changed and made up with professional hexagon crimps. Try to keep it the same length as the positive link. However you have still not explained why you think one battery is not charging to its full extent. Please try to be a little more specific in your questions and answers.

Edited October 6, 2015 by Tony Brooks

[tommytelford]

Sorry I have not replied to your comments before Tony but life has been a bit hectic of late.

 

I have not been back to the boat for while but I am pretty sure that the feeds are not as you state, I think that the the positive feeds are from both batteries, I assumed that this was ok as they are linked but next time I am aboard I will transfer them all to the same terminal and see what hapens

[Tony Brooks]

Sorry I have not replied to your comments before Tony but life has been a bit hectic of late.

 

I have not been back to the boat for while but I am pretty sure that the feeds are not as you state, I think that the the positive feeds are from both batteries, I assumed that this was ok as they are linked but next time I am aboard I will transfer them all to the same terminal and see what hapens

 

Of course both batteries or battery banks have a positive feed. On battery or bank from position 1 on the switch and the other battery or bank from position two. Both will be connected together with the switch in the both position. I assume that one "battery" is a bank of two or more and to optimise charging on a multi-battery bank the positive leads go to one battery and the negatives to the other. Both battery or battery banks negatives should be joined.

 

A single battery would normally be classed as the start battery while a bank of two or more or the larger battery would be designated the domestic or house battery (ies).

 

The negative cable joining the two banks should have a conductor cross sectional area of 25 sq mm to comply with the BSS.

 

A domestic or house battery or bank would normally take several hours to recharge. The engine battery less than an hour. Are you sure that you are running for enough time?

[tommytelford]

Sorry Tony I think I may have misunderstood or not made myself clear. I have one starter battery and a bank of 2 which have separate feeds through the changeover switch.

On the bank of 2 batteries the negatives are linked and grounded and one of the batteries has the positive feed from the alternator (via the changeover switch) and the charger / inverter, the other battery has the positive feed to the domestic fusebox and the 2 battery positives are linked by a heavy cable.

The starter battery has the positive cable from the changeover switch and the feed to the starter solenoid and a negative earth cable as normal.

I have tried it out by fully charging the batteries from the charger but with the TV on for about an hour, the lights on for maybe three hours (mostly leds), and the fridge turned to low the batteries just about last overnight

[Tony Brooks]

Sorry Tony I think I may have misunderstood or not made myself clear. I have one starter battery and a bank of 2 which have separate feeds through the changeover switch.

On the bank of 2 batteries the negatives are linked and grounded and one of the batteries has the positive feed from the alternator (via the changeover switch) and the charger / inverter, the other battery has the positive feed to the domestic fusebox and the 2 battery positives are linked by a heavy cable.

The starter battery has the positive cable from the changeover switch and the feed to the starter solenoid and a negative earth cable as normal.

I have tried it out by fully charging the batteries from the charger but with the TV on for about an hour, the lights on for maybe three hours (mostly leds), and the fridge turned to low the batteries just about last overnight

 

OK, lets hope this is a GRP or wooden boat because it seems that the domestic return current may be passing through the hull to the engine block (possibly via the control cables) and then back to the alternator or in reverse for any loads.

 

Unless you have two alternators (and even then its not best practice on a metal boat) the two bank negatives are normally linked via a heavy battery style cable so there is only one earth point to the hull. Actually with flexible engine mounts you may end up with one earth to the engine and a second to the hull. The cable connection the two bank's (engine and domestic) negatives should have a conductor cross sectional area of at least 25 sq mm to meet BSS requirements.

 

Your domestic bank of two batteries should have all its positive connections on one battery and all its negatives on the other. However with just two batteries this is not so vital as with more but it will to a small degree compromise the charge and discharge of one of the batteries if they are not so connected. The TWO interlinks between the two domestic batteries should be in 25 sq mm CSA or larger cable. If you only have one interlink then either it is not connected positive to positive or all the other positive and negative cables are connected to one battery while the other one is not being charged or discharged. If there is only one interlink it would be connected positive on one battery to negative on the other to give 12V from 2 x 6 volt batteries or 24V from 2 x 12 volt batteries.

 

Whichever connection on your 1, 2, both, off switch (1 or 2) the pair of batteries are connected to is designated the domestic bank and when the engine is not running the switch should connect to that bank. When the engine is running the switch should be in the both position so all three batteries are charged.

 

If you are correct about the two banks not having their negatives linked then you could easily have excessive resistance (voltdrop) on the charging circuit of one bank (probably the domestic one) and that would prevent it being properly charged. This voltdrop would most likely be in the negative side of the circuit.

 

I suggest that you go onto my website, look in the Electrical Notes and study the TWO diagrams of how such systems are normally wired. Then make sure that whichever way your system is using the switch complies with the diagram. Sometimes the switch is used just to switch the charge but then for BSS purposes you should have master switches or it is used to switch the whole electrical loads and charge from one bank, the other, or both banks.

 

If the system has been miswired for more than a few weeks it is very likely that at least one battery has suffered sulphation so now has far less capacity than the label states.

 

If you have problems with the diagram why not draw your system and post it here. At the moment a good start would be a photo of the domestic bank.

Edited November 17, 2015 by Tony Brooks

[tommytelford]

The two domestic batteries are linked with the same size cable for negative and positive and both bank negatives are connected to the earth stud on the starter motor as is the alternator, the same way as is found on many road vehicles. The hull is not used as an earth link at all.

 

If your previous suggestions don't work I will provide a drawing for clarity

[Tony Brooks]

The two domestic batteries are linked with the same size cable for negative and positive and both bank negatives are connected to the earth stud on the starter motor as is the alternator, the same way as is found on many road vehicles. The hull is not used as an earth link at all.

 

If your previous suggestions don't work I will provide a drawing for clarity

 

OK so both banks negatives are joined with heavy cable but for some reason using the starter earth stud as a junction box. That should be fine as long as the stater terminal is clean and tight.

 

You do have two interlinks on the domestic bank of what sounds like adequate size so that should be OK.

 

As the domestic bank is only of two batteries it is less important where the positive and negative charging AND load wires are connected but best practice says they should be on opposite ends of the bank, not both on the same battery.

 

That all seem reasonable and not likely to cause a single battery to charge less than the other two so although charging cable size and length may be involved there is no way to work on that without an indication of cable size, length and maximum alternator output. (I can't go back and look at the first page of responses because it would delete this reply).

 

I do not recall the actual battery being identified. Is it one of the domestic batteries, the start battery or maybe both domestic batteries.

 

We are left with faulty battery, lack of charging, or operator error re the 1, 2, both, off switch. from the comments about the TV only running for a couple of hours it sounds as if its both domestic batteries that are playing up and based on experience that is far more likely to be caused by batteries that are sulphated so they now only have a fraction of their stated capacity. That is caused by leaving them in a less than fully charged state over a longish period. The question is why? Over discharge, insufficient charging time, insufficient alternator output (for the time the engine is run), or incorrect use of the big switch.

 

It is possible that one of the domestic batteries has an internal short circuit, especially if they have been regularly discharged to well below 12.2 volts or are more than three years old (assuming so called leisure batteries).

 

I would suggest that you do a power/energy audit for your use of your boat and then the battery bank size and charging calculations samples and explanations of which you will find in the maintenance notes on my website. Then post the results.