Fusing alternator charging cables

[stranded]

May I begin by repeating publicly my appreciation to Sandy for braving the elements on Sunday and coming over to my boat to help me diagnose a charging issue. It was great to meet such a lovely bloke and his input was invaluable.

The problem is that while the alternator seems to more or less charge the cranking and windlass/thruster batteries, it never really does better than maintain the 400ah house bank (at whatever state of discharge) no matter how long we are motoring for. I think with the info that Sandy gleaned I have identified the issue as general undercharging due to voltage drop across the multi battery diode isolator - we measured 13.8v to all batteries. So my first approach is to replace the diode isolator with a zero drop Sterling Pro Split R, largely because Nigel Calder seems to rate them. This looks simple enough to fit, even for an electrical dunce like me, except for one thing - fuses, which Sterling stipulate.

Currently, only the windlass/thruster alternator feed is fused at the battery. Neither of the others seem to be. All three go through individual battery isolation switches. As usual, my hopes of a simple answer courtesy of Google were dashed as advocates and opponents of fusing the alternator output at the battery seem to be about 50/50. Since the main objection to fusing seems to be the risk of blowing the alternator if the fuse fails, a risk reduced by the Pro Split redirecting the output I believe, I am inclined to fit Cube fuses on the battery post of the house and starter batteries. Sterling I think say say to size at 150% +50A of maximum possible current (I assume they mean working current rather than dead short). As I will be fusing all input and output from the battery, I presume that this means the maximum conceivable current draw rather than the alternator output?

i Think thats it really, unless anyone has any helpful advice to save me from my own ignorance!

Cheers, Mark

 

[William_H]

If only to bump your question... yes it would be desirable to fit fuses at the battery pos. post of each battery. The fuse size needs to be commensurate with the cable size coming from it and the max expected current. Yes diodes in the distribution lines to the batteries for charging will reduce the voltage by .7 volt for silicon diodes most common or about .3 for schotky diodes, for charging so you need to bypass these diodes. (switch VSR or zero drop splitter)The other option is to change the alternator voltage sensing to battery sensing which in effect raises the charge voltage to give 14v at the battery even with diode losses. Assuming all batteries are charged via diodes then sensing at one battery should give a suitable voltage for all batteries.
Regarding alternator output fusing. A short to negative at the output is not likely to cause a fire as alternator output is naturally limited. However when this wire is also connected to the battery positive there is the current source of the battery which can be huge causing the wire to incandesce and cause a fire. Hence fuses at each battery are far safer. (protecting all the wiring ) ol'will

 

[stranded]

Cheers for the help Ol’will - that’s good enough for me. The cables are pretty massive so I’m going to go for 300A Fuses, which should cover everything and still be within cable capacity. Mark

 

[Refueler]

Split Diode charging ... yep .. I have a good split diode unit mounted in my boat ... I connected all up ... and found exact same thing - it barely charged my two 90 A/Hr batts up ...
I investigated and found that the split diode system was basically causing a Voltage drop of about 0.7V and alternator as far as it was concerned was doing its job at ~14.5+ ... but of course out from diodes was 13.5 'ish ...

I thought about doing the sensing cheat of a diode on the alternator ... but in the end as the diode splitter was a freebie from a pal - I just disconnected and put all back as it was originally. The diode unit just sits there now.

 

[stranded]

Split Diode charging ... yep .. I have a good split diode unit mounted in my boat ... I connected all up ... and found exact same thing - it barely charged my two 90 A/Hr batts up ...
I investigated and found that the split diode system was basically causing a Voltage drop of about 0.7V and alternator as far as it was concerned was doing its job at ~14.5+ ... but of course out from diodes was 13.5 'ish ...

I thought about doing the sensing cheat of a diode on the alternator ... but in the end as the diode splitter was a freebie from a pal - I just disconnected and put all back as it was originally. The diode unit just sits there now.

So you have reverted to manual switches? I did think about that but I just know I would forget to switch over. If the Pro-Split doesn’t do it I might reconsider though!

 

[Refueler]

So you have reverted to manual switches? I did think about that but I just know I would forget to switch over. If the Pro-Split doesn’t do it I might reconsider though!

If I post about this honestly - >

I'm old school and have never had problems on any boat I have had ... simple two battery system fed to the old fashioned rotary 1-Both-2-Off switch ...
I have a toggle switch in my starter box that connects power to my start button ... that in turn of course energises the solenoid to start.
I have an LED and buzzer in the alternator excite lead which go out once revs are upped to trigger alternator to charge.
I have a car relay that cuts in as well to power my cold box from the alternator.

Battery monitoring is by a simple 1 - off - 2 toggle switch with analogue meter ...

The only connections I have that are live when my main battery switch is at OFF :

1. Auto - Manual locally switched bilge pump
2. Old fashioned non auto 4A mains battery charger that feeds via a solid state charge splitter (bought in Maplins many years ago designed to manage caravans batterys) that also shuts off whichever battery is full charged.

I am fully aware that there are 'better' systems - but mine is simple and I like it that way !! Next owner - if boat lasts longer than me can do what they like with it !!

 

[stranded]

If I post about this honestly - >

I'm old school and have never had problems on any boat I have had ... simple two battery system fed to the old fashioned rotary 1-Both-2-Off switch ...
I have a toggle switch in my starter box that connects power to my start button ... that in turn of course energises the solenoid to start.
I have an LED and buzzer in the alternator excite lead which go out once revs are upped to trigger alternator to charge.
I have a car relay that cuts in as well to power my cold box from the alternator.

Battery monitoring is by a simple 1 - off - 2 toggle switch with analogue meter ...

The only connections I have that are live when my main battery switch is at OFF :

1. Auto - Manual locally switched bilge pump
2. Old fashioned non auto 4A mains battery charger that feeds via a solid state charge splitter (bought in Maplins many years ago designed to manage caravans batterys) that also shuts off whichever battery is full charged.

I am fully aware that there are 'better' systems - but mine is simple and I like it that way !! Next owner - if boat lasts longer than me can do what they like with it !!

As my old headteacher used often to say, with little effect tbh, honesty is the best policy!

My sympathies do lie more towards your KISS approach - I find the complexity of our electrical system utterly baffling, but that probably says more about me than anything. It is essentially as we bought it and mostly it works fine so I am sticking with a like for like replacement policy on the electrical side, getting more modern components where they will slot in, as here, but steering well clear of any changes which might have unintended consequences elsewhere. This was our first (and I hope will be our last) boat and I think we did in our ignorance think more is more. I would take a different approach if circumstances meant we did have to look for a replacement.

 

[PaulRainbow]

A Victron Argofet is almost a drop in replacement for the old diode pack, might need to re-crimp the odd terminal and will need a simple negative wire fitting.

 

[Refueler]

As my old headteacher used often to say, with little effect tbh, honesty is the best policy!

My sympathies do lie more towards your KISS approach - I find the complexity of our electrical system utterly baffling, but that probably says more about me than anything. It is essentially as we bought it and mostly it works fine so I am sticking with a like for like replacement policy on the electrical side, getting more modern components where they will slot in, as here, but steering well clear of any changes which might have unintended consequences elsewhere. This was our first (and I hope will be our last) boat and I think we did in our ignorance think more is more. I would take a different approach if circumstances meant we did have to look for a replacement.

At times I do look at that diode block sitting there and wonder should I bother ....

I don't like the sensing from one battery .... seems a bit ?? when I have a dual bank.

Cheating the alternator by adding a diode itself to deliver compensated voltage ... maybe ... but I'm no alternator guru !

There's fitting another unit ...

Then I have a beer and think - it works ...

 

[stranded]

A Victron Argofet is almost a drop in replacement for the old diode pack, might need to re-crimp the odd terminal and will need a simple negative wire fitting.

Thanks Paul - I did look at that but opted for the Sterling. That too is almost a drop in - just add a negative line for the electronics and an ignition sensing line. Not that I am taking such challenges lightly!

 

[[70521]]

May I begin by repeating publicly my appreciation to Sandy for braving the elements on Sunday and coming over to my boat to help me diagnose a charging issue. It was great to meet such a lovely bloke and his input was invaluable.

It was a pleasure meeting you Mark, you made a cracking mug of tea on a foul day.

When I've got my soft furnishings back from the upholster, sorted out my rewire (and thanks to PaulRainbow for his advice and I really need to call halcyon at KDD Power and sort out my new switch panel) you must pop over for a dram.

 

[lw395]

Split Diode charging ... yep .. I have a good split diode unit mounted in my boat ... I connected all up ... and found exact same thing - it barely charged my two 90 A/Hr batts up ...
I investigated and found that the split diode system was basically causing a Voltage drop of about 0.7V and alternator as far as it was concerned was doing its job at ~14.5+ ... but of course out from diodes was 13.5 'ish ...

I thought about doing the sensing cheat of a diode on the alternator ... but in the end as the diode splitter was a freebie from a pal - I just disconnected and put all back as it was originally. The diode unit just sits there now.

When I first got one of my boats, there was a diode splitter wired across the 1b2 switch. So, if you selected '1', battery one got direct output of 14.3V from the alternator, while battery two, which would be the engine start battery that day got a float voltage of 13.7V.
It might actually make sense if you motored a lot or often had shore power. Myself I motored not very much and kept the boat on a swinging mooring. So I changed the alternator and experimented with the regulator sensing.
If you were aggressively charging a house bank at 14.8V, a diode drop to the already charged engine battery starts to look right.
But there are easier ways.
The big flaw with diode splitters is that the more charged battery, which doesn't need charging gets more volts than the other, because the diode drop is not constant.

 

[stranded]

When I first got one of my boats, there was a diode splitter wired across the 1b2 switch. So, if you selected '1', battery one got direct output of 14.3V from the alternator, while battery two, which would be the engine start battery that day got a float voltage of 13.7V.
It might actually make sense if you motored a lot or often had shore power. Myself I motored not very much and kept the boat on a swinging mooring. So I changed the alternator and experimented with the regulator sensing.
If you were aggressively charging a house bank at 14.8V, a diode drop to the already charged engine battery starts to look right.
But there are easier ways.
The big flaw with diode splitters is that the more charged battery, which doesn't need charging gets more volts than the other, because the diode drop is not constant.

And that is the trouble with bloody electrics - you think you are getting a handle on something then some completely new variable enters the picture. Doesn’t matter to me now because I am entering my post-diode period, but this is something I have not read anywhere else but makes absolute sense - so battery sensing (from one battery) and adjusting the regulator voltage to compensate is not the panacea it first appears.

 

[PaulRainbow]

And that is the trouble with bloody electrics - you think you are getting a handle on something then some completely new variable enters the picture. Doesn’t matter to me now because I am entering my post-diode period, but this is something I have not read anywhere else but makes absolute sense - so battery sensing (from one battery) and adjusting the regulator voltage to compensate is not the panacea it first appears.

It isn't, but you get close if you sense the domestic bank.

 

[Refueler]

As I say - I am not so comfortable with sensing from one battery when I have two to maintain ...

If I was more savvy with the back end of an alternator - I might add the diode there to fool the alternator to compensate - then I know that both batterys will get the required charge.

Better still - for me - leave the diode splitter alone !!