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Alternator / Battery wiring question

chunkyj

By chunkyj
in Boat Equipment

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chunkyj Explorer

chunkyj

Posted
Posted

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

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Tony Brooks Veteran II

Tony BrooksDonate to Canal World

Posted
Posted

Also you are probably overcomplicating it by asking for starter battery charging priority. Starting an engine in good condition only takes few Amp Hours so that is normally replaced long before the doemstic bank is charged up. Just parallel the alternators as in thread above but accept that one MIGHT shut down once the regulators start working.

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Graham.m Rising Star

Graham.m

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Also you are probably overcomplicating it by asking for starter battery charging priority. Starting an engine in good condition only takes few Amp Hours so that is normally replaced long before the doemstic bank is charged up. Just parallel the alternators as in thread above but accept that one MIGHT shut down once the regulators start working.

 

Tony,

 

Is there any reason why the two alternators should not charge their respective batteries, start - domestic and be paralleled by a Cyrix Battery Combiner or similar at the appropriate time. Could that not deal with the OPs concern about charging the starter battery?

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Tony Brooks Veteran II

Tony BrooksDonate to Canal World

Posted
Posted

 

Tony,

 

Is there any reason why the two alternators should not charge their respective batteries, start - domestic and be paralleled by a Cyrix Battery Combiner or similar at the appropriate time. Could that not deal with the OPs concern about charging the starter battery?

 

None whatsoever but the Cyrex is just a bi-directional voltage sensitive relay when I last looked and if either battery was well charged enough to allow one alternator's charging voltage to reach the cyrex closing voltage then the Cyrex would close. I think this is typically between about 13.4 and 13.6 volts. In most situations it would be the engine battery alternator that would have the lowest charge (thus highest voltage first) but maybe after prolonged starting problems or a failing engine battery it could be the doemstic.

 

This is a simple and straight forward solution but may not always meet the "engine battery charged first" requirement which is why I tried to explain why that is not a s important as many people AND marketing types try to make out. In fact I doubt it would ever meet that criteria but in the majority of situations it would be absolutely fine.

 

If engine battery priority charging is so vital I just wonder how those of us with split charge relays are not always having engine battery problems.

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WotEver Veteran II

WotEverDonate to Canal World

Posted
Posted

 

Tony,

 

Is there any reason why the two alternators should not charge their respective batteries, start - domestic and be paralleled by a Cyrix Battery Combiner or similar at the appropriate time. Could that not deal with the OPs concern about charging the starter battery?

There would be absolutely no point. The starter battery would take very little time to recharge as has already been said. The instant the banks are paralleled you are back to where you started.

 

Sure, you can use a VSR to do 'automatic' paralleling if you wish but I maintain there is no point. You could also use a VSR in the opposite configuration to disconnect the paralleling once the batteries have reached acceptance. It's all unnecessary complication though and just more to go wrong.

 

If OP has a SmartGauge then Smartbank can offer automatic paralleling for him if he wishes.

 

Tony

If engine battery priority charging is so vital I just wonder how those of us with split charge relays are not always having engine battery problems.

A very good point, well made.

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GUMPY Veteran II

GUMPYDonate to Canal World

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I run two alternators 90 and 70amp on one engine both set up to have exactly the same regulator voltage and charging two sets of batteries, I have a VSR that senses from the domestics and combines the two once the domestics are above 13.5 volt

Advantages

Appears to get maximum charge into batteries in minimum time.

When starter alternator started playing up the other covered it.

When on landline the VSR allows the use of one charger to charge both banks.

haven't found any disadvantages yet

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Graham.m Rising Star

Graham.m

Posted
Posted (edited)

 

None whatsoever but the Cyrex is just a bi-directional voltage sensitive relay when I last looked and if either battery was well charged enough to allow one alternator's charging voltage to reach the cyrex closing voltage then the Cyrex would close. I think this is typically between about 13.4 and 13.6 volts. In most situations it would be the engine battery alternator that would have the lowest charge (thus highest voltage first) but maybe after prolonged starting problems or a failing engine battery it could be the doemstic.

 

This is a simple and straight forward solution but may not always meet the "engine battery charged first" requirement which is why I tried to explain why that is not a s important as many people AND marketing types try to make out. In fact I doubt it would ever meet that criteria but in the majority of situations it would be absolutely fine.

 

If engine battery priority charging is so vital I just wonder how those of us with split charge relays are not always having engine battery problems.

 

Thanks Tony, I was just trying to look at the OP's specific request that the starter battery is favoured rather than the domestics, which seemed to be getting ignore by that's not the way we do it thoughts. It seemed a reasonable compromise to me.

There would be absolutely no point. The starter battery would take very little time to recharge as has already been said. The instant the banks are paralleled you are back to where you started.

 

Sure, you can use a VSR to do 'automatic' paralleling if you wish but I maintain there is no point. You could also use a VSR in the opposite configuration to disconnect the paralleling once the batteries have reached acceptance. It's all unnecessary complication though and just more to go wrong.

 

If OP has a SmartGauge then Smartbank can offer automatic paralleling for him if he wishes.

 

Tony

 

A very good point, well made.

 

See above

Edited by Graham.m
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sjc Engager

sjc

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My preference , just to give you another option would be to keep the starter and domestic circuits separate. Keep one of the 70A alternators as a spare, buy a new 140A ( or so, depends on bank capacity ) alternator for the domestics and hey presto. Ensure the pulley ratios are high for the domestics to get the most out of it. One thing to consider when fully loading your starter alternator is that the belt also drives the water pump ( usually ), high currents mean more tension in the belt, and more wear on the bearings, which is why I suggest leaving the starter system alone - I am sure Tony can advise whether this is a genuine concern ?

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Tony Brooks Veteran II

Tony BrooksDonate to Canal World

Posted
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My preference , just to give you another option would be to keep the starter and domestic circuits separate. Keep one of the 70A alternators as a spare, buy a new 140A ( or so, depends on bank capacity ) alternator for the domestics and hey presto. Ensure the pulley ratios are high for the domestics to get the most out of it. One thing to consider when fully loading your starter alternator is that the belt also drives the water pump ( usually ), high currents mean more tension in the belt, and more wear on the bearings, which is why I suggest leaving the starter system alone - I am sure Tony can advise whether this is a genuine concern ?

 

Personally I would draw the line at no more than 90 amp alternators on singe V belts for reasons of life and re-tensioning. I know many people run larger ones but that maybe fine if you can guarantee that you will always get high quality belts. I am not is sure the local "parts place" or even chandlers would be sure to stock real quality belts. I suspect those with larger alternator on single V belts may well over tension them and put just as much strain in the water pump bearings.

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