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rowland al

Charging of domestic batteries

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I have 2 x 6v newish Trojans (T105) in series for domestic and one 12v starter battery on a separate circuit. 

I've found that after I start the engine , the amp meter reads 20A plus charging for a minute or so then creeps back to 1-2 amps within a couple of minutes. This I expect as the the alternator is working hard to replace the energy used for starting.

What I don't understand is that even when the 2 x Trojan domestic batteries are down to about 12.1 volts, the amp meter only shows about 1 to 2A charging current after a few minutes from starting. I would have thought it would be much higher until they are also charged up like the stater battery. 

The alternator seems fine as shown by the high initial charging current when trying to replenish the stater battery.

I'm pretty sure this has been the same over the last 5 years with 2 other sets of  batteries. They do charge up but I'm wondering if they could be charging up more efficiently given the low charging current. 

Confused!? :-(

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What do you have linking the banks together?    It’s better to have the alternator going to the main batteries rather than the starter.

also where is the amp meter measuring from?

Edited by Robbo

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What is the alternator voltsge when delivering 20 amps and again when it has dropped to 2-3 amps? It may be that the regulator is set too low.

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Not enough info but if what you say is true then I suspect:-

1. Its a twin alternator boat with the ammeter on the engine alternator.

2. If a single alternator boat then as Robbo says either the ammeter is in the wrong part of the wiring OR your charge splitting device has failed but in the latter case the batteries should have been flat long ago.

3. Unlikely today but its just possible your electrical needs are so low they can be satisfied by exceptionally heavily sulphated Trojans so they are fully charged in such a short time but this is very unlikely.

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37 minutes ago, cuthound said:

What is the alternator voltsge when delivering 20 amps and again when it has dropped to 2-3 amps? It may be that the regulator is set too low.

It reads 14.1 volts when the engine has just been started and 14.4 volts after the starter battery has been replenished (2-3 mins) 

42 minutes ago, Robbo said:

What do you have linking the banks together?    It’s better to have the alternator going to the main batteries rather than the starter.

also where is the amp meter measuring from?

The big thick charging wire goes to the domestics. 

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I suspect twin alternators but only the ammeter in the engine panel which monitors the starter alternator.  The second alternator should go direct to the domestic bank and doesn't normally get fitted with an ammeter although in my opinion it is vital to look after the batteries life.  The voltmeter on the engine control panel will also be connected to the starter battery.

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4 minutes ago, rowland al said:

It reads 14.1 volts when the engine has just been started and 14.4 volts after the starter battery has been replenished (2-3 mins) 

The big thick charging wire goes to the domestics. 

And where does the amp meter get its measurement from?   If it’s from the starter battery negative then the figures you quoting sound right.

Can you check with a clamp multi meter on what the alternator is actually giving out?

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20 minutes ago, Tony Brooks said:

Not enough info but if what you say is true then I suspect:-

1. Its a twin alternator boat with the ammeter on the engine alternator.

2. If a single alternator boat then as Robbo says either the ammeter is in the wrong part of the wiring OR your charge splitting device has failed but in the latter case the batteries should have been flat long ago.

3. Unlikely today but its just possible your electrical needs are so low they can be satisfied by exceptionally heavily sulphated Trojans so they are fully charged in such a short time but this is very unlikely.

1) It's single alternator 

2) Domestic batteries do get charged but takes about 6 hours engine time to get them from 12.1v to 12.6v (standing).  This surprises me given I'm only using 2 x T105's. Ampmeter could be in wrong place but I haven't had a chance to reverse engineer the circuit into a diagram yet.

3) The Trojans are being used and drop to 12.1v ish after an evenings use as expected. 

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3 minutes ago, rowland al said:

1) It's single alternator 

2) Domestic batteries do get charged but takes about 6 hours engine time to get them from 12.1v to 12.6v (standing).  This surprises me given I'm only using 2 x T105's. Ampmeter could be in wrong place but I haven't had a chance to reverse engineer the circuit into a diagram yet.

3) The Trojans are being used and drop to 12.1v ish after an evenings use as expected. 

That is 450 Ah when new and 12.1 rested is under half charged so without considering sulphation that'd about 225 Ah plus say 20 or 30% for charging efficiency to put back in so say 270Ah of charge required. As a single alternator is probably in the range of 50 to 70 amps output, average over 3 to 4 hours of 25 to 35 amp, then I am not surprised its taking you 6 hours to get to around 80% fully charged. I also strongly suspect the figures are wrong because of sulphation.

With a single 70 amp alternator charging 330Ah of domestic battery and 100 Ah of engine battery I usually get to about 12.7 volts (rested) by the end of a day's cruise (say 6 hours or so) and its often around 12.3 to 12.5 the following morning.

I suspect not enough charging time and ammeter in the wrong place.

If you have a means of equalising those Trojans please   do  so ASAP, it might recover so of the suspectd sulphation.

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12 minutes ago, Tony Brooks said:

That is 450 Ah when new and 12.1 rested is under half charged so without considering sulphation that'd about 225 Ah plus say 20 or 30% for charging efficiency to put back in so say 270Ah of charge required. As a single alternator is probably in the range of 50 to 70 amps output, average over 3 to 4 hours of 25 to 35 amp, then I am not surprised its taking you 6 hours to get to around 80% fully charged. I also strongly suspect the figures are wrong because of sulphation.

With a single 70 amp alternator charging 330Ah of domestic battery and 100 Ah of engine battery I usually get to about 12.7 volts (rested) by the end of a day's cruise (say 6 hours or so) and its often around 12.3 to 12.5 the following morning.

I suspect not enough charging time and ammeter in the wrong place.

If you have a means of equalising those Trojans please   do  so ASAP, it might recover so of the suspectd sulphation.

Sorry Tony for being a bit thick this end but I don't understand a lot of your reply.

I think you are suggesting that it is reasonable for a 70a alternator to take 6 hours to get the domestics back up to 12.6v from 12.1v even though I am just using 2 x T105's!

Where should the ampmeter be? What is sulphination and it's effects? Also what is equalisation? 

Even more confused here now but much appreciate you all getting back to me. Plain English please for those who are hard of thinking like me. :)

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9 minutes ago, Mike the Boilerman said:

 

Surely a mistake here. Trojans T105s are 225 AH at 6v each, and the OP has two in series. That makes 225AH at 12v as I understand it.

I think you are right. It would be 450Ah capacity at 6v. 225Ah at 12v. 

Maybe Tony assumed I was running 4 x T105's. 

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Again, I do appreciate everyone's replies here. 

So, two basic questions I can't get my head around. 

1) Why does the ampmeter show 20a charging a minute or so after starting from the starter battery, but only shows 1 to 2 amps charging when the domestic batteries are only 50%. Ampmeter in wrong place then? I should point out we are talking old fashioned analog ampmeter here, not digital. 

It makes no sense to me. The starter battery must be near 100% all of the time so would need less charge. Surely a higher charge current would be shown for the more depleted domestic batteries. 

2) Would it be better for me to charge my domestics using my 240v generator (run via belt off engine) and a battery charger than just my alternator? If so, I suppose that means a battery charger run off 240v is  more efficient than just using my 70a alternator? 

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Yes Mike - Tony the pratt. Brain fart, forgot they would be in series so all my calculations need halving.

Rowland, I agree now the batteries should be well charge in 6 hours but 12.6V says they are not or if they are you have  a fair load on them so they it is not a rested voltage. The 12.1 volts  suggest that you may be over discharging them if you go that low regularly. That in turn suggest an undersized battery bank. This all assumes a charging voltage in excess of about 14,2 volts or more towards the end of the day.

Sulphation - when a lead acid battery is discharged the lead oxide on one set of the plates turns to lead sulphate, when you charge it it turns back to lead oxide.  However the longer the battery is left in any state of discharge the physically harder the sulphate becomes and the higher the voltage required to fully reconvert it to lead oxide. At any sensible battery charging voltage you reach a stage where some can not be reconverted. The lead sulphate can then no longer "store" electricity so the battery capacity is reduced. This   is known as sulphation. A higher voltage as when you equalise the batteries (say 15 + volts will reconvert at least some of the lead sulphate so you regain a little capacity.

Many ammeters on boats are not really suitable and contribute to under battery charging. They should really be those that use a  remote shunt and the measure the volt drop across the shunt that will be proportional to the current flowing through the shunt. The meter is calibrated in amps.

A ammeter measuring the domestic batteries charge/discharge will normally be fitted in the negative lead to the domestic back but some may use a different technology and/or demand fitting in the positive side. This is not good because it demands fuses in both thin wires that connect the shunt to the meter or you risk burning the boat out if either wire developed a short circuit. The fuses MIGHT the because the meter to under read by an unknown degree.

A single tick wire should run from the domestic battery negative that is fitted on the shunt. Every other negative wire should be fitted to the other end of the shunt.

If you look behind your present ammeter it will either have two thin wires connected to it (good) or two much thicker  wires, say pencil size or above (bad). There is one make of ammeter that has the shunt across the back of it so it will have thick wires but it is far from ideal voltdrop on wiring wise. If the ammeter has thick wires then the charging circuit will need rewiring  to allow a shunted ammeter to be fitted. Such meters are usually round with a 50-050 scale on them and they are not any better than a very rough indication of charging current.They are not suitable for any serious monitoring. If you have one of these come back and I will try to explain how to rewire so it shows the domestic battery charging current.

My (and others) guess is that your ammeter is between the  charge splitter (lapse tell us what type this is) and the engine battery so it never sees the domestic charge. It needs to go between the alternator and domestic battery assuming the alternator output runs direct to the domestic battery or  in the   domestic battery negative before the start battery negative joins it. If its the type I suspect it is then it is likely to be on the positive side unless the alternator is a fully insulated return unit which is not so likely.         

 

Edited by Tony Brooks

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16 minutes ago, Tony Brooks said:Yes Mike - Tony the pratt. Brain fart, forgot they would be in series so all my calculations need halving.

Rowland, I agree now the batteries should be well charge in 6 hours but 12.6V says they are not or if they are you have  a fair load on them so they it is not a rested voltage. The 12.1 volts  suggest that you may be over discharging them if you go that low regularly. That in turn suggest an undersized battery bank. This all assumes a charging voltage in excess of about 14,2 volts or more towards the end of the day.

Sulphation - when a lead acid battery is discharged the lead oxide on one set of the plates turns to lead sulphate, when you charge it it turns back to lead oxide.  However the longer the battery is left in any state of discharge the physically harder the sulphate becomes and the higher the voltage required to fully reconvert it to lead oxide. At any sensible battery charging voltage you reach a stage where some can not be reconverted. The lead sulphate can then no longer "store" electricity so the battery capacity is reduced. This   is known as sulphation. A higher voltage as when you equalise the batteries (say 15 + volts will reconvert at least some of the lead sulphate so you regain a little capacity.

Many ammeters on boats are not really suitable and contribute to under battery charging. They should really be those that use a  remote shunt and the measure the volt drop across the shunt that will be proportional to the current flowing through the shunt. The meter is calibrated in amps.

A ammeter measuring the domestic batteries charge/discharge will normally be fitted in the negative lead to the domestic back but some may use a different technology and/or demand fitting in the positive side. This is not good because it demands fuses in both thin wires that connect the shunt to the meter or you risk burning the boat out if either wire developed a short circuit. The fuses MIGHT the because the meter to under read by an unknown degree.

A single tick wire should run from the domestic battery negative that is fitted on the shunt. Every other negative wire should be fitted to the other end of the shunt.

If you look behind your present ammeter it will either have two thin wires connected to it (good) or two much thicker  wires, say pencil size or above (bad). There is one make of ammeter that has the shunt across the back of it so it will have thick wires but it is far from ideal voltdrop on wiring wise. If the ammeter has thick wires then the charging circuit will need rewiring  to allow a shunted ammeter to be fitted. Such meters are usually round with a 50-050 scale on them and they are not any better than a very rough indication of charging current.They are not suitable for any serious monitoring. If you have one of these come back and I will try to explain how to rewire so it shows the domestic battery charging current.

 

 

 

Oh gawd, I'm really struggling now.

To take your points in turn Tony.

I was lead to believe (no pun intended) that lead acid batteries like to run between 50% and 100%. Being a 'real' CC'er (no controversy intended), we do charge them up for around 5-6 hours a day. I understood this was a good thing. 

The measurements I gave you are indeed at resting (standing).I never go below 12.0v. So I don't think they are being discharged too much, I don't think the battery bank is too small for purpose (no electric fridge, washing machine or dishwasher. who I pay anyway) and the normal charging voltage is 14.4V.

Thanks for your explaination of sulphation, that makes a lot of sense but we don't leave the batteries for more than a few days.

All understood on my old ampmeter arrangement. That might be misleading me. What's a remote shunt and 'tick' wire?

Still confused but now learning something. :)

 

 

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Tick wire = thick wire (typo).

You have decent batteries which were quite expensive, and a lot more expensive now with the £$ exchange rate. But what you lack is adequate means of monitoring what they’re doing, how they are being charged etc. You (and we) are clutching in the dark because you have no means of knowing what current is flowing in or out of the domestic batteries. I would therefore recommend that you buy and install a battery monitor such as a NASA BM1 of Victron BMV700 series. Then we will no longer have to guess!

Edited by nicknorman
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6 minutes ago, rowland al said:

Oh gawd, I'm really struggling now.

To take your points in turn Tony.

I was lead to believe (no pun intended) that lead acid batteries like to run between 50% and 100%. Being a 'real' CC'er (no controversy intended), we do charge them up for around 5-6 hours a day. I understood this was a good thing. 

The measurements I gave you are indeed at resting (standing).I never go below 12.0v. So I don't think they are being discharged too much, I don't think the battery bank is too small for purpose (no electric fridge, washing machine or dishwasher. who I pay anyway) and the normal charging voltage is 14.4V.

Thanks for your explaination of sulphation, that makes a lot of sense but we don't leave the batteries for more than a few days.

All understood on my old ampmeter arrangement. That might be misleading me. What's a remote shunt and 'tick' wire?

Still confused but now learning something. :)

 

 

12.0 volts rested voltage equates to 25% state of charge, so you have been discharging your batteries more than you thought. If left at this SoC for long it will lead to sulphation.

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11 minutes ago, cuthound said:

12.0 volts rested voltage equates to 25% state of charge, so you have been discharging your batteries more than you thought. If left at this SoC for long it will lead to sulphation.

From what I understand you are incorrect, maybe 40% but not 25%. Anyway 12.1v is my trigger to charge up, 

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19 minutes ago, nicknorman said:

Tick wire = thick wire (typo).

You have decent batteries which were quite expensive, and a lot more expensive now with the £$ exchange rate. But what you lack is adequate means of monitoring what they’re doing, how they are being charged etc. You (and we) are clutching in the dark because you have no means of knowing what current is flowing in or out of the domestic batteries. I would therefore recommend that you buy and install a battery monitor such as a NASA BM1 of Victron BMV700 series. Then we will no longer have to guess!

I get what you are saying, but my main questions are in my post 13. I.e

Again, I do appreciate everyone's replies here. 

So, two basic questions I can't get my head around. 

1) Why does the ampmeter show 20a charging a minute or so after starting from the starter battery, but only shows 1 to 2 amps charging when the domestic batteries are only 50%. Ampmeter in wrong place then? I should point out we are talking old fashioned analog ampmeter here, not digital. 

It makes no sense to me. The starter battery must be near 100% all of the time so would need less charge. Surely a higher charge current would be shown for the more depleted domestic batteries. 

2) Would it be better for me to charge my domestics using my 240v generator (run via belt off engine) and a battery charger than just my alternator? If so, I suppose that means a battery charger run off 240v is  more efficient than just using my 70a alternator? 

 

 

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5 minutes ago, rowland al said:

From what I understand you are incorrect, maybe 40% but not 25%. Anyway 12.1v is my trigger to charge up, 

Trojan would agree with you :)

T105_Trojan_Data_Sheets.pdf

2 minutes ago, rowland al said:

Ampmeter in wrong place then?

Sounds like it. 

3 minutes ago, rowland al said:

Would it be better for me to charge my domestics using my 240v generator (run via belt off engine) and a battery charger than just my alternator?

Shouldn’t be, not with 6 hours charging every day. 

What you do need though is a decent way of monitoring the batteries. 

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Is it just possible there an issue with so called 'domestic' batteries?

Has anyone actually tried using starter batteries as domestic? 

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5 minutes ago, rowland al said:

Has anyone actually tried using starter batteries as domestic? 

That’s all a cheap domestic is. Just with a different badge. 

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33 minutes ago, rowland al said:

From what I understand you are incorrect, maybe 40% but not 25%. Anyway 12.1v is my trigger to charge up, 

Having checked with the Trojan T105 data sheet you are correct. The figure I gave is a generic one for wet lead acid batteries, but specific manufacturers recommendations can differ.

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3 minutes ago, WotEver said:

That’s all a cheap domestic is. Just with a different badge. 

Well for one, I was told a domestic battery could get ruined if you use it to start an engine. For another, I'm pretty sure the last domestic battery I bought cost more than my starter. 

So confusing! 

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2 minutes ago, rowland al said:

Well for one, I was told a domestic battery could get ruined if you use it to start an engine. For another, I'm pretty sure the last domestic battery I bought cost more than my starter. 

So confusing! 

There are domestics, and there are domestics. Did you see that caravanner article that Pete posted a week or so back?

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