Alternative charging circuit

[hugoman56]

Has anyone had experience of a new alternator to batteries charging configuration? It connects the output of the alternator directly to the house batteries and also uses the split charge diodes in parallel to charge the engine battery (at slightly lower voltage obviously). The advantages that have been explained to me are that a) the house batteries charge faster/fuller. b) The house batteries are able to 'top-up' the engine battery when starting. Any thoughts welcome.

 

[duncan99210]

Welcome to the forum.
I think you may be talking about a Voltage Sensitive Relay, which more or less does what you’re talking about. There’s usually a thread running on the topic somewhere on here. Someone with more knowledge than I have will no doubt be along to join in....
For what it’s worth,I have a Sterling Alternator to Battery fitted between my alternator and batteries. It charges the engine battery first before diverting the charge to the domestic bank. Works for me, others have different solutions.

 

[PaulRainbow]

Has anyone had experience of a new alternator to batteries charging configuration? It connects the output of the alternator directly to the house batteries and also uses the split charge diodes in parallel to charge the engine battery (at slightly lower voltage obviously). The advantages that have been explained to me are that a) the house batteries charge faster/fuller. b) The house batteries are able to 'top-up' the engine battery when starting. Any thoughts welcome.

Not exactly a new configuration, just a half arsed attempt to overcome the voltage drop across the diodes.

The domestic batteries will almost certainly charge faster, (assuming a standard alternator setup, no battery sensing or external regulator), because the domestic batteries will not suffer the voltage drop. The engine battery will still be wired through the diode, so will be subjected to the voltage loss. A downside to this is that the engine and domestic batteries will be wired in parallel, albeit the current can only flow in one direction, so a faulty engine battery can flatten all batteries, even if the isolators are all off (unless the charging is wired across the isolators, in which case you must never turn the isolators off with the engine running.

A better solution would be to fit a modern split charging system. There are various options, such as a VSR or a low loss splitter (this is usually a drop in replacement for a diode pack, with an added negative wire), what is most suitable will depend on your existing setup.

 

[Jokani]

Surely, a 1-2-Both switch is the way to go?

Fuse lit, time to run ;-)

 

[pvb]

Surely, a 1-2-Both switch is the way to go?

You know better than that! Sadly, a lot of the dyed-in-the-wool brigade might agree.

 

[halcyon]

You know better than that! Sadly, a lot of the dyed-in-the-wool brigade might agree.

I'm not saying a word.

Brian

 

[PaulRainbow]

Surely, a 1-2-Both switch is the way to go?

Fuse lit, time to run ;-)

 

[Quandary]

Not much bullshit there?

 

[hugoman56]

I am asking because I have a sterling regulator already (been working great for 15 years), but my alternator died and I am reluctant to crack open the new alternator to add the sense wire at the moment. This seems a reasonable compromise pro tem and is actually shown (in German only) on the back of the sterling instruction manual and is labelled 'my favourite configuration'.

 

[pvb]

I am asking because I have a sterling regulator already (been working great for 15 years), but my alternator died and I am reluctant to crack open the new alternator to add the sense wire at the moment. This seems a reasonable compromise pro tem and is actually shown (in German only) on the back of the sterling instruction manual and is labelled 'my favourite configuration'.

Yes, you can wire it that way. If you have a brand new alternator it will hopefully have a voltage regulated to 14+v, so you'll get a reasonable charge rate into your house batteries. I wouldn't worry too much about the voltage reaching your starter battery - cars and vans happily run all day long with their alternators churning out 14+v. The diodes will reduce voltage slightly, but only slightly, as the volt drop does vary according to current, and starter batteries don't take much current as they're usually fairly full.

However, as PaulRainbow has highlighted, this doesn't isolate your starter battery and if it develops a faulty cell, it could drain all your batteries.

 

[hugoman56]

Yes, you can wire it that way. If you have a brand new alternator it will hopefully have a voltage regulated to 14+v, so you'll get a reasonable charge rate into your house batteries. I wouldn't worry too much about the voltage reaching your starter battery - cars and vans happily run all day long with their alternators churning out 14+v. The diodes will reduce voltage slightly, but only slightly, as the volt drop does vary according to current, and starter batteries don't take much current as they're usually fairly full.

However, as PaulRainbow has highlighted, this doesn't isolate your starter battery and if it develops a faulty cell, it could drain all your batteries.

Yes, I hadnt thought about the engine battery failing. The new alternator is putting out 14.6 V but with cable and diode losses the house batteries are charging to 13.8 which is typically their float charge voltage. I think I'll try it and see. If not happy I'll crack the new alternator and fit the field wire. I've done three before but it's always a worry when it's brand new.