Battery Wiring

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chunky86

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HI Guys,
I am currently looking at rewiring my 12v.
What is the best way to wire up 2 alternators from 2 separate engines to charge my batteries.
I am looking for a system that will fully charge the starter battery bank before charging the domestics and I would like to make the most of the 2 70A alternators

Thanks in advance

:)
 
There are a couple of alternatives that meet your requirement.

One is to install a voltage sensing relay (VSR) which charges the starter battery until it reaches a set voltage (equivalent to a state of charge) then kicks in to charge the main domestic bank.
Efficient, simple, reasonable cost, fairly reliable.

Option 2 is to install a charger like this
http://sterling-power.com/collections/alternator-to-battery-chargers
Full explanation on their website when you follow the link, but in brief it splits the charge to the 2 banks, and boosts charge to the domestic bank to charge it more quickly and completely.

One feature of both alternatives listed above is that they will work fully even if one engine fails - an important feature which you need to consider.
I opted for option 2, fitted it about 5 years ago and it's been very good.
Edit: Option 2 gives a better charging regime compared to option 1 (with standard alternators) and therefore gives more battery capacity and better battery care unless you upgrade the charging system inside the alternators, which is also a possibility but a bit more complicated.

One thing to bear in mind is that you'll need to upgrade some of your battery wiring from alternators to charger and batteries to cope with the increased charging current, but that's about the only extra.
 
Last edited:
Thanks for both suggestion, problem is I need full charging capacity from either engine regardless of the number of engines running.
i.e. both alternators wired to charge the starter bank (2 x 110aH) first then the domestics (4 x 125aH)
With the product Keith-i recommends it is almost ideal but I need the grunt of 2 batteries to start the engines and that needs a separate battery for each engine :(
Trundlebug ; Is the system you have linked to designed for twin engines, each with its own alternator?

Cheers
 
chunky86 said:
Thanks for both suggestion, problem is I need full charging capacity from either engine regardless of the number of engines running.
i.e. both alternators wired to charge the starter bank (2 x 110aH) first then the domestics (4 x 125aH)
With the product Keith-i recommends it is almost ideal but I need the grunt of 2 batteries to start the engines and that needs a separate battery for each engine :(
Trundlebug ; Is the system you have linked to designed for twin engines, each with its own alternator?

Cheers
Click to expand...

Yes the alt to batt charger is designed for twin engined inputs.
In fact you just connect both alternators to the one input of the charger and it sorts everything out.
If one engine fails you still have full charging capability, if not full capacity.
But in reality you'll rarely if ever need the max output of both alternators, so max capacity is largely irrelevant except when specifying the size of charger.
 
Trundlebug said:
Yes the alt to batt charger is designed for twin engined inputs.
In fact you just connect both alternators to the one input of the charger and it sorts everything out.
If one engine fails you still have full charging capability, if not full capacity.
But in reality you'll rarely if ever need the max output of both alternators, so max capacity is largely irrelevant except when specifying the size of charger.
Click to expand...

If you link two alternator to a common point you get hunting, no regulators are identical, once regulation point for lower unit is reached it will cut out. The remaining alternator load increases causing a volt drop and the the other alt cut back in and so on.

You can charge the engine start bank from one engine and the service bank from the second engine, VSR cuts in to link engine bank alternator to service bank at voltage. When the charge to the service bank drops to a low level the VSR will drop, leaving the engine alt charging the engine battery. If service voltage drops it will cut back in to support service alternator, if engine alt fails it will cut in to charge engine bank from service alt.

They do twin engine alt to battery chargers in the USA, but they use two independent inputs to avoid hunting.

Brian
 
Thanks Trundlebug, it sounds like exactly what I'm looking for :)
Did you also go for the optional remote kit?

Halcyon; My situation is a little different to most of you guys as I won't always be running both engines, we also do a lot of smaller river cruising and twin v8's is a little overkill! Hence the wanting for both engines being able to do everything, this then gives me the availability to vary which engine I run when river cruising :)
 
halcyon said:
If you link two alternator to a common point you get hunting, no regulators are identical, once regulation point for lower unit is reached it will cut out. The remaining alternator load increases causing a volt drop and the the other alt cut back in and so on.

You can charge the engine start bank from one engine and the service bank from the second engine, VSR cuts in to link engine bank alternator to service bank at voltage. When the charge to the service bank drops to a low level the VSR will drop, leaving the engine alt charging the engine battery. If service voltage drops it will cut back in to support service alternator, if engine alt fails it will cut in to charge engine bank from service alt.

They do twin engine alt to battery chargers in the USA, but they use two independent inputs to avoid hunting.

Brian
Click to expand...

Is hunting a problem? Not in my real world experience. Regulators cut in and out all the time anyway - that's what they're supposed to do.
I have had my set up with 2 engine alternators wired into the alt to batt charger for about 6 years now, no ill effects.
Easy to install, and total flexibility if either engine fails you still have full charge management.
As I said in post #2, VSR's are an alternative.
 
Trundlebug said:
Is hunting a problem? Not in my real world experience. Regulators cut in and out all the time anyway - that's what they're supposed to do.
I have had my set up with 2 engine alternators wired into the alt to batt charger for about 6 years now, no ill effects.
Easy to install, and total flexibility if either engine fails you still have full charge management.
As I said in post #2, VSR's are an alternative.
Click to expand...

No two installations are the same, just pointing out a problem that can exists with twin alternators charging a common point, same as what happens if alt to batt or VSR unit fails, problems that need considering with new installation.

Brian
 
Dougal Tolan said:
2 x 70A alternators charging 2 x 110 Ah batteries, isnt that a bit fast? Given the max charge current should be 10% of capacity rule....
Click to expand...

Nope. The batteries will only take as much current as they need - you can't 'force' current in.

Voltage is the sensitive thing, you CAN (easily) apply to much voltage, then problems happen.
 
sorry chaps, my posts still needed to be approved by a mod before showing!

my replies should now be posted where I did reply if that makes sense :D
 
Replying to your earlier question, no I didn't go for the Sterling remote panel.

I fitted a NASA BM-1 battery monitor and that tells me everything I need to know. It was also a lot cheaper than the Sterling remote, IIRC.
 
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