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Battery Charging

Ammonite

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New sense wire installed. I'm now getting 14.4v at the house bank which is good and 14.7v at the starter battery which I understand is the very top end for a SLA. I'm still get the 0.8v voltage drop between the input and outputs on the splitter.
 

PaulRainbow

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New sense wire installed. I'm now getting 14.4v at the house bank which is good and 14.7v at the starter battery which I understand is the very top end for a SLA. I'm still get the 0.8v voltage drop between the input and outputs on the splitter.
The volt drop across the splitter isn't great, but the battery sensing is allowing for it. It's a little odd your are seeing 14.7 at the starter battery.
 

Ammonite

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The volt drop across the splitter isn't great, but the battery sensing is allowing for it. It's a little odd your are seeing 14.7 at the starter battery.
Any idea why I'm seeing 14.7v at the starter battery? I deliberatelyset the 1-2-Both switch to 2 when testing this (and I would expect the same result with separate isolators) and as expected I'm seeing 14.4v across both banks when I set the switch to both so it seems to happen when there is no load on the starter bank. The only odd thing I've noticed about the current starter battery is that it will sit for several weeks at 12.9v whereas all the others settle around 12.7/8v. I've verified this with both the BM1 where measures both banks and a decent multimeter.

I could try switching the outputs of the splitter? If the problem is specific to the engine output it should be resolved as the Cyrix parallels the house and thruster batteries so in effect they are both sensed?
 
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PaulRainbow

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With the switch on "both", i assume you meant both, not "2", the batteries are in parallel and will read the same voltage.

I would take any battery voltage measurements at the batteries, with the multimeter.

When you are seeing 14.7V and 14.4V at the batteries, what do you see at the alternator ? Are there any loads on the domestic bank ? What SOC are the domestic batteries ?
 

Alex_Blackwood

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With the switch on "both", i assume you meant both, not "2", the batteries are in parallel and will read the same voltage.

I would take any battery voltage measurements at the batteries, with the multimeter.

When you are seeing 14.7V and 14.4V at the batteries, what do you see at the alternator ? Are there any loads on the domestic bank ? What SOC are the domestic batteries ?
I am not being funny but seriously suggest that the OP needs a professional to look at this system!
 

Ammonite

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With the switch on "both", i assume you meant both, not "2", the batteries are in parallel and will read the same voltage.

I would take any battery voltage measurements at the batteries, with the multimeter.

When you are seeing 14.7V and 14.4V at the batteries, what do you see at the alternator ? Are there any loads on the domestic bank ? What SOC are the domestic batteries ?
I could have worded it better but we're saying the same thing. 14.4v all round when on Both. 14.7v at the starter battery and 14.4v at the house bank when on 2. Voltages measured at the batteries. 15.4v at the alternator while testing this and 1.8amp load on the house bank. All batteries fully charged although as highlighted above the starter battery starts off at 12.9v and the house at 12.8v.

It seems to me that my options are to:-

Live with it or just try switching the splitter outputs although I'm not overly happy about the 0.8v splitter voltage drop which is supposed to be max 0.25v according to the manual

Fit an Argofet for circa £100, particularly if switching the existing outputs resolves the starter and house bank 0.3v difference.

Remove the splitter. Move the Cyrix so it's between starter and house banks. Fit a B2B charger between house and thruster batteries for circa £200.
 
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Ammonite

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I am not being funny but seriously suggest that the OP needs a professional to look at this system!
A professional is looking at the system - albeit virtually and I'm confident in my abilities to work out what is connected to what. I also really appreciate Paul's advice and it will hopefully benefit many others.

This is PBO and I'm really keen to learn. I'm going through all the TB training guides while posting on here.

A "professional" fitted the current setup with battery sense wire running via the 1-2-Both switch to the starter solenoid and the professional I used to check out a previous electrical problem was useless and I had to sort it myself - successfully.

If Paul was local or I knew someone I trust locally I would consider it, subject to the comments above!
 
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Alex_Blackwood

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A professional is looking at the system - albeit virtually and I'm confident in my abilities to work out what is connected to what. I also really appreciate Paul's advice and it will hopefully benefit many others.

This is PBO and I'm really keen to learn. I'm going through all the TB training guides while posting on here.

A "professional" fitted the current setup and the professional I used to check out a previous electrical problem was useless and I had to sort it my self - successfully.

If Paul was local or I knew someone I trust locally I would consider it, subject to the comments above!
Don't get me wrong, I wasn't knocking you, or what you are trying to achieve. In fact I applaud your efforts and fully appreciate Paul's input and expertise. It just seemed to me from reading through the threads that you have maybe more than one problem and an "On site" aspect may be beneficial. That is by the way my professional opinion:)
 
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PaulRainbow

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I could have worded it better but we're saying the same thing. 14.4v all round when on Both. 14.7v at the starter battery and 14.4v at the house bank when on 2. Voltages measured at the batteries. 15.4v at the alternator while testing this and 1.8amp load on the house bank. All batteries fully charged although as highlighted above the starter battery starts off at 12.9v and the house at 12.8v.

It seems to me that my options are to:-

Live with it or just try switching the splitter outputs although I'm not overly happy about the 0.8v splitter voltage drop which is supposed to be max 0.25v according to the manual

Fit an Argofet for circa £100, particularly if switching the existing outputs resolves the starter and house bank 0.3v difference.

Remove the splitter. Move the Cyrix so it's between starter and house banks. Fit a B2B charger between house and thruster batteries for circa £200.
What are the exact makes/models of domestic and starter battery ?

It might be interesting to swap the engine and domestic connections on the splitter.
 

halcyon

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What are the exact makes/models of domestic and starter battery ?

It might be interesting to swap the engine and domestic connections on the splitter.
If domestic is bank 2, assume engine bank 1 ?, how is he getting 14.7 on a isolated battery, back feed somewhere ?

Brian

PS He has a splitter does he not, engine has a very low current so diode volt drop smaller, voltage higher, asnwered my own point.
 
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PaulRainbow

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If domestic is bank 2, assume engine bank 1 ?, how is he getting 14.7 on a isolated battery, back feed somewhere ?

Brian

PS He has a splitter does he not, engine has a very low current so diode volt drop smaller, voltage higher, asnwered my own point.
He's getting 15.4V at the alternator and is sensing the domestic bank, so the 14.7V at the domestic bank is a result of voltage drop across the diode. With no sensing possible at the engine battery it will get the 15.4V alternator voltage, minus any voltage drop between the splitter and the engine battery. You're right that with very little current going to the engine battery the drop would be smaller, although he says the domestics are fully charged too, so not much current there. I'd suspect enough of a current difference to have an effect though and the small load on the domestics would also have an effect. I suspect there may be some differences in the battery chemistry too, which could also have an effect.

I'll be interested to hear what the makes/models of batteries are.
 

Ammonite

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Don't get me wrong, I wasn't knocking you, or what you are trying to achieve. In fact I applaud your efforts and fully appreciate Paul's input and expertise. It just seemed to me from reading through the threads that you have maybe more than one problem and an "On site" aspect may be beneficial. That is by the way my professional opinion:)
Thanks Alex. Sounds to me like you are trying to drum up business 🤔
Joking aside, you're right there have been a number of problems and although it may not sound like it I like to understand each problem and solve them in turn, with the assistance of the forum of course as well as reading around the subject. In fact I like getting my head around what's going and enjoy this almost as much as the sailing which is why the forum is such a valuable resource. I also couldn't afford to sail the boat I do without doing most of the work myself although if I'm truly stumped or likely to injure myself I will call in a pro. Unfortunately I've also had several bad experiences in recent years with the electrician I mentioned and more recently a fridge engineer.

Anyway by way of an update...
The alternator was the first problem. It had been uprated to produce 14.8v. I have now replaced this with a 70amp Prestolite.
The second problem was the battery sensing wire which had been connected to the starter solenoid so that it sensed via the 1-2-Both switch. I have now moved this to the domestic battery and its reading correctly.
The third problem...and the prize goes to Paul again, albeit indirectly, is that despite having identical batteries for the starter and house banks (Numax XV31MF 105Ah all of the same age -apologies I said 110Ah before) the starter battery was still reading 14.7v, against the house 14.4v when the battery switch was on 2. However having just replaced the starter battery with another 110amp SLA (I recently removed this to fit an AGM for the Thruster) it is working perfectly and I have 14.4v on both banks with the switch still on 2! I'm guessing here but could the fact that the previous starter battery has been charged at over 15v for the last year have turned it into some form of mutant super battery, or a dud 😀

So the only problem I seem to have left is the voltage drop across the splitter which is still 0.8v against a quoted max 0.25v drop and rather than replace it with an Argofet I'm leaning towards spending a bit more to get the battery to battery charger so that I have the correct charging regime for the AGM in the bow, which will removing the splitter and putting the Cyrix betweenthe starter and house....or I could just leave it with the voltage drop for now?
 
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PaulRainbow

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So the only problem I seem to have left is the voltage drop across the splitter which is still 0.8v against a quoted max 0.25v drop and rather than replace it with an Argofet I'm leaning towards spending a bit more to get the battery to battery charger so that I have the correct charging regime for the AGM in the bow, which will removing the splitter and putting the Cyrix betweenthe starter and house....or I could just leave it with the voltage drop for now?
Don't forget that you'll be getting a voltage drop on the 4m cable run, so the splitter isn't as bad as 0.8V. Fact is, having the sense wire correctly connected is giving you the correct voltages at the batteries, so i'd leave it as it is. I also wouldn't worry about the AGM battery, the vast majority of boats out there that are fitted with AGM batteries are charging them at SLA voltages. Technically, it's a touch low, but i doubt if you could calculate the effect that will have on the batteries overall life expectancy. I'd say, job done
(y)
 

Ammonite

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He's getting 15.4V at the alternator and is sensing the domestic bank, so the 14.7V at the domestic bank is a result of voltage drop across the diode. With no sensing possible at the engine battery it will get the 15.4V alternator voltage, minus any voltage drop between the splitter and the engine battery. You're right that with very little current going to the engine battery the drop would be smaller, although he says the domestics are fully charged too, so not much current there. I'd suspect enough of a current difference to have an effect though and the small load on the domestics would also have an effect. I suspect there may be some differences in the battery chemistry too, which could also have an effect.

I'll be interested to hear what the makes/models of batteries are.
Hi Paul
That's not quite right. I "was" ( see update above) seeing 15.4v at the alternator, 14.4v at the (sensed) house bank and 14.7v at the (unsensed) starter battery. Now that I have replaced the starter battery today both banks are at 14.4v (with the 1-2-Both) switch on 2 (house). I still have a 0.8v drop across the splitter but the alternator is now outputting 15.2v. These readings are all at 1500rpm with circa 1.8amp load on the house bank and none on the starter battery.
 

Ammonite

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Don't forget that you'll be getting a voltage drop on the 4m cable run, so the splitter isn't as bad as 0.8V. Fact is, having the sense wire correctly connected is giving you the correct voltages at the batteries, so i'd leave it as it is. I also wouldn't worry about the AGM battery, the vast majority of boats out there that are fitted with AGM batteries are charging them at SLA voltages. Technically, it's a touch low, but i doubt if you could calculate the effect that will have on the batteries overall life expectancy. I'd say, job done
(y)
Thanks for bearing with me! I really appreciate the help :)
 

PaulRainbow

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Hi Paul
That's not quite right. I "was" ( see update above) seeing 15.4v at the alternator, 14.4v at the (sensed) house bank and 14.7v at the (unsensed) starter battery. Now that I have replaced the starter battery today both banks are at 14.4v (with the 1-2-Both) switch on 2 (house). I still have a 0.8v drop across the splitter but the alternator is now outputting 15.2v. These readings are all at 1500rpm with circa 1.8amp load on the house bank and none on the starter battery.
OK, i still wouldn't worry, the batteries are getting the voltage they need, maybe the splitter people fibbed, it happens.
 

Ammonite

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Do you know what your 1-2-Both switch actually does? What's it for?
Is that a trick question? 🤔
The BOTH and OFF functions are excellent 😀. The 1 and 2 positions are a PITA which is why I shall be replacing it with separate isolators and a means of linking the two if needed. I currently leave it on 2 mostly as the starter battery is charged via the splitter and the shunt on the house bank doesn't object to starting the engine as long as it starts readily although I'd prefer not to subject the electronics to this. If I was turning over the engine for longer I'd select 1. I think there are enough threads on the subject(!) without creating another one and I've no idea why someone appears to have retrofitted a 1-2-Both switch. I think the boat originally had separate isolators and a heavy duty relay to charge both banks.
 

pvb

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Is that a trick question? 🤔
The BOTH and OFF functions are excellent 😀. The 1 and 2 positions are a PITA which is why I shall be replacing it with separate isolators and a means of linking the two if needed. I currently leave it on 2 mostly as the starter battery is charged via the splitter and the shunt on the house bank doesn't object to starting the engine as long as it starts readily although I'd prefer not to subject the electronics to this. If I was turning over the engine for longer I'd select 1. I think there are enough threads on the subject(!) without creating another one and I've no idea why someone appears to have retrofitted a 1-2-Both switch. I think the boat originally had separate isolators and a heavy duty relay to charge both banks.
Not a trick question at all. But your reply suggests that you think it directs the alternator charging to one or both of the batteries. Yet you have a splitter which does this automatically. As others have suggested, I think you'd benefit from asking a professional to check the system over.
 

Ammonite

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Not a trick question at all. But your reply suggests that you think it directs the alternator charging to one or both of the batteries. Yet you have a splitter which does this automatically. As others have suggested, I think you'd benefit from asking a professional to check the system over.
No I don't :) and as Paul has indicated the problem is now solved. The sense wire on the regulator had been removed from the B+ output on the alternator and wired directly to the starter motor solenoid rather than directly to the house bank (the B+ on the alternator goes directly to the splitter). It was therefore "sensing" whatever battery was selected on the 1-2-Both switch while charging both through the splitter. Throw in a 0.2v voltage drop through the battery switch and its not surprising it wasn't sensing the voltage correctly. It was further confounded by an alternator that had been modified to produce 14.8v
 
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