Alternator D+ advice sought, please!

[WotEver]

 

Tony, thank you for that. I don't have the mental clarity, right now, to think it through from my armchair, but it reads like it's important enough to look at tomorrow. I DO apologise, but I'm suffering from Alcohol-Induced Dickhead Syndrome and it will take it's own time to recover.

 

I've set a reminder on me phone for tomorrow!

Tony was simply pointing out that the diode should be between D+ and the relay ONLY and to be careful that it wasn't in the warning lamp circuit. The simplest way to achieve that would be to solder it to the relay base.

 

Tony

[Sir Nibble]

 

I wondered if you might chip in, Snibs!

 

I presume your idea is to put the fuse between the relay common and the changeover switch common terminal? So that the relay coil is fuse protected in either switch position?

 

(I am slightly slower on the uptake than either of Wotever and Nicknorman!) ETA: And Tony B!

I mean the fuse in line B+ to switch to protect the circuit downstream. A fuse won't protect your relay, only the wiring.

[Loafer]

Thank you for your help chaps. My ageing brain is edging ever closer to Sir Nib's fused switch arrangement. It seems simpler and I don't have to order a diode, which for me represents a postage faff.

 

Snibs, your...

 

I mean the fuse in line B+ to switch to protect the circuit downstream. A fuse won't protect your relay, only the wiring.

 

...is understood, thank you.

 

Final answer? Any dissenters from Snib's idea?

[nicknorman]

Well only that it depends on where the switch is relative to the alternator. If you take the power feed from B+ and it has to be routed all the way to an engine panel somewhere, switched, then all the way back to the relay (which is likely to be near the alternator) it would surely be easier to use the engine 12v supply already extant at the panel (and already fused), ie the permanently live side of the "ignition switch", then you just need 1 long wire not 2. But as I said, it depends on where the bits are located.

[Loafer]

Well only that it depends on where the switch is relative to the alternator. If you take the power feed from B+ and it has to be routed all the way to an engine panel somewhere, switched, then all the way back to the relay (which is likely to be near the alternator) it would surely be easier to use the engine 12v supply already extant at the panel (and already fused), ie the permanently live side of the "ignition switch", then you just need 1 long wire not 2. But as I said, it depends on where the bits are located.

 

Good stuff there Nick. My relay is in the battery box along with both battery banks. The alternators are on the other side of the engine room. The panel is my green one in the middle which you may have seen in my earlier photograph.

 

The switch will be bunged right in the middle of it all. I'm about to go and fiddle with it!

[dmr]

Going right back to the start....

As was said the starter battery would not normally sulphate and also a high voltage charge/equalise will shorten the life of the starter battery which only has thin plates, but I really don't know if this is a significant effect or not. My last starter battery lasted at least 7 years and never got equalised.

Whilst you are installing new switches in your lovely control panel, can you also install one to disable the alternator joining (if you don't already have one)?. As you know, Trojans like charging at 14.8 or even 15 volts, plus periodic equalising, whilst the starter will be happy with about 14.6 or even a bit less, 14.8 will only cause water loss and maybe plate wear with no real advantage. Ideally the alternators should be shorted during the bulk phase to provide maximum current to the domestic bank, and then split once the voltage exceeds about 14.6.v.

If you want to be really clever then there is a programmable relay within your smartgage and you could use this to automatically disable the alternator parallel at higher voltages. This is on my list of things to do, I currently have a switch but I keep forgetting to turn it off.

 

................Dave

[Loafer]

Going right back to the start....

 

...If you want to be really clever then there is a programmable relay within your smartgage and you could use this to automatically disable the alternator parallel at higher voltages. This is on my list of things to do, I currently have a switch but I keep forgetting to turn it off.

 

................Dave

 

 

Ah yes, but as yet I don't have a Smartgauge. However, that's a good idea, Dave.

 

I think on reflection, I'm wasting my time with this manual bus-tie option. I'm now on plan B, which is to use the switch on the 'lovely panel' to switch the posh voltmeter from domestic bank to starter bank.

 

You know, just for kicks!

[WotEver]

I'm now on plan B, which is to use the switch on the 'lovely panel' to switch the posh voltmeter from domestic bank to starter bank.

Ooh, that gives the opportunity for TWO lights - one for each bank.

[Loafer]

Ooh, that gives the opportunity for TWO lights - one for each bank.

 

Oooh, don't get me excited, Wotever!

I've sorted my manual relay thing. The two battery bank positives are 6" apart. I have a jump lead in the battery box now. Sorted!