charging 2 battery banks with 2 engines

[pappaecho]

I am trying to get my head around two engine alternators charging both the starter battery bank, and the leisure bank. Easy enough with one alternator and a diode splitter, but how do you combine two alternators to charge two banks, without them confusing the charge levels.
I know that I can buy a box for £365, but is there a more simple way?

 

[aquatom]

I would fit a Merlin Smart Bank system it links the battery banks when it detects either of them are being charged. Works great for 1,2 or 3 engines with 2 or 3 battery banks.

Very simple and easy to install.

 

[aquapower]

can be done using two of the mastervolt charge splitters, very simple and reliable

http://www.mastervolt.com/view_product.php?lang=2&section=mobile&prggr_id=1021&prg_id=1048&pro_id=5180

 

[oldgit]

Kiss ?

The good old Princess principle of keep it simple (ie.cheap) involves what looks suspiciously like 2 x alternators in parallel charging 6 batteries in parallel from what I can see under the saloon floor.
It seems to have worked OK for the last 30 years on my boat.

 

[Cookee]

I would fit a Merlin Smart Bank system it links the battery banks when it detects either of them are being charged. Works great for 1,2 or 3 engines with 2 or 3 battery banks.

Very simple and easy to install.

Merlin are at : 01202 697979 and are in Poole if that helps

 

[sarabande]

have a look at the excellent Vetus catalog, p 154. It shows the set up for two engines.

http://viewer.zmags.com/publication/fd2b8fee#/fd2b8fee/154

 

[pappaecho]

Thanks guys specially Oldgit, as I was not sure what happened if two alternator outputs were paralleled. The answer appears to be "not a lot" .

 

[oldgit]

Thanks guys specially Oldgit, as I was not sure what happened if two alternator outputs were paralleled. The answer appears to be "not a lot" .

When my volt meter(s) announced recently that no charge was going to batteries, removed both ancient 45A Valeo alternators.
One of them was a manky rust ball inside and had obviously not been working for years and years and BER.
The other was sort of OK inside and had been doing the job of two for quite some time,however as need to sort immediately,did not bother to rebuild but bought two new ones(ISKRA) with much higher Amp capacity.
Curiously enough 2 old duff units went to Slovina via Ebay for rather good money?

 

[PaulGooch]

Thanks guys specially Oldgit, as I was not sure what happened if two alternator outputs were paralleled. The answer appears to be "not a lot" .

You don't parallel the alternators. You connect each alternator to a split charge diode, then the diode outputs from each diode connect to each battery bank.

 

[oldgit]

You don't parallel the alternators. You connect each alternator to a split charge diode, then the diode outputs from each diode connect to each battery bank.

It must be well hidden, as in 8 years of ownership and several half hearted searches have been unable to discover any trace of anything other than direct feeds from alts to batts ?
Will have another look,given vintage suspect I am looking for an encapsulated project box of some description,but given amount of amps must be blimming substantial.

 

[PaulGooch]

It must be well hidden, as in 8 years of ownership and several half hearted searches have been unable to discover any trace of anything other than direct feeds from alts to batts ?
Will have another look,given vintage suspect I am looking for an encapsulated project box of some description,but given amount of amps must be blimming substantial.

It might be the case that one engine charges the starter bank and the other charges the domestic bank.

Princess wouldn't have paralleled the alternators and wired them to both banks, as this would have the affect of paralleling both battery banks, resulting in one large bank.

The benefit of wiring as per my diagram would largely be that the engine batteries would be fully charged very quickly, after which all alternator output would be directed at the domestic bank.

 

[A_8]

I have been struggling with the same question. From factory my boat had separate systems, one generator for the starter circuit and the other for the domestic batteries.

In the nordics we spend a lot of time on island without shore-power and with a 500Ah domestic bank, a 60Ah VP std generator one soon realize after a couple of days on an island it will be many hours running the engine to fully charge the batteries.

The question was then to upgrade the generator to a 150Ah type or....maybe use the one on the other engine, it is pretty much doing nothing most of the time.

It was difficult to get a clear answer if you could just parallel the generators, the issue was if they would both sense a full charge and basically cut back with no difference in overall charging current.

I decided to try, got a voltage sensitive relay, it basically cuts in if the voltage goes over 13.2 volts so in effect it connects all the batteries with both generators when the engines are running and I am now getting a massive charge current into my domestic bank, I can not measure above 100Ah and the meter goes beyond its range.

It works just fine so in my experience you can parallel the generators with added charging as a bonus.

Of course you may want a separate starter battery so perhaps using a voltage sensitive relay to make sure they get disconnected when the engines are not running is a better solution then just wiring it all together.






I

 

[PaulGooch]

VSR's have no place on a boat. As soon as the engine starts, the VSR will energise and effectively parallel the battery banks. If a single battery catastrophically fails it could suck the power out of all the batteries in both banks. If the battery the VSR is trying to charge develops a fault and won't hold a proper charge, the VSR has to carry all the current that this bank requires from the other bank. It isn't designed to carry such loads, nor is the wiring used. If, for instance, the bank that the VSR is charging has the windlass on it, as soon as you hit the windlass control the VSR or the wiring will be fried (hopefully the wiring won't catch light, but it could easily do so as there is no circuit breaker or fuse specified in the typical fitting instructions.

As a pertinent example, we had a battery fail at the beginning of a 150 nm trip at the end of last Summer. When we arrived at an overnight stop 45 nm into the journey i switched the engine off and all of the electronics went off. The electronics battery was totally flat, despite being charged for the past three hours by the alternator. Had we have been using a VSR, it's almost certain that the dead battery would have sucked the life out of the good engine battery. We hooked up to the shore power and the battery was on charge all night via the 25a mains charger. In the morning it was still flat as a pancake. As soon as the engine was started, everything worked fine and we were able to complete the trip, with the totally knackered battery, no problems at all.

 

[Cari bean Pie rat.]

From what you desribe they are 2 separate systems so you will not be paralleling the alternators but if you want do as PaulGooch suggests.
From my limited knowledge if you connect 2 votage sources and there is a voltage difference between said sources then you have problems because of V=IR.
i.e. The R will be small figure like 0.001 Ohms and if the V is like 1 or 2 you have a large value of I which is current and this will do the damage to cables , connectors and all.

 

[A_8]

My main point was that you can parallel two generators. My solution with the VSR was a low cost test. I think there are more intelligent battery management systems out there but they also cost you a lot more.
Having said that and if you add a fuse that matches the VSR and cables, probably around 150Ah you have safe installation.

 

[PaulGooch]

My main point was that you can parallel two generators. My solution with the VSR was a low cost test. I think there are more intelligent battery management systems out there but they also cost you a lot more.
Having said that and if you add a fuse that matches the VSR and cables, probably around 150Ah you have safe installation.

Whilst it's possible, it isn't good practice to parallel the alternators, voltage sensing issues have the potential to give problems. As for the VSR, i'm sorry but there is no suck thing as a safe VSR installation on a boat. While it's working, it seems to be a good, cheap solution and it does indeed keep all the batteries charged up. But, all the time you are under way, every battery on the boat is paralleled, that is dangerous as it could leave you stranded at sea.

No one would wire a boat up with a single battery bank, that had to start both engines and run all the domestic/electronic circuits, but that is what you do by fitting a VSR. Why do you think none of the major builders use VSR's ?

 

[A_8]

Whilst it's possible, it isn't good practice to parallel the alternators, voltage sensing issues have the potential to give problems. As for the VSR, i'm sorry but there is no suck thing as a safe VSR installation on a boat. While it's working, it seems to be a good, cheap solution and it does indeed keep all the batteries charged up. But, all the time you are under way, every battery on the boat is paralleled, that is dangerous as it could leave you stranded at sea.

No one would wire a boat up with a single battery bank, that had to start both engines and run all the domestic/electronic circuits, but that is what you do by fitting a VSR. Why do you think none of the major builders use VSR's ?

I should probably have said a reasonably safe installation, i.e. it will keep the relay and cables from burning up. It will however not help charge your batteries if they are dead, not sure any solution will fix this though. In my world you check the batteries every now and then to make sure they are good when you need them which will make sure you do not get stranded.

It is still two separate battery banks, that is exactly what the VSR's are designed to make possible, particularly when you only have one generator. The VSR connects the batteries when the voltage goes above 13.8 volts and disengages when it goes under 12.8 which keeps them separate when there is no charge, thus making sure you always have power to start (again provided your batteries are ok and will accept the charge currents)

I've seen many single generator boats with similar solutions, i.e. connecting the starter and domestic bank when the generator is charging. In some cases its as simple as a relay that closes when the generator lamp goes out. Many use a diode splitter but then you get the issue of a voltage drop to the battery that do not have the voltage sensing on it which may or may not shorten the battery life. Or similarly to your fears with the VSR leave you stranded with a dead starter battery.

Again, there are better ways and I would not recommend anyone using a VSR unless you fully understand how your boat is wired and how the currents will flow given all possible scenarios. That includes the voltage sensing for the generators or you may get issues.

In my case I am only testing so far but I am getting 120Ah charge on tap to my domestic bank at almost no cost, the alternative was to rebuild the generator set up on one engine which would have been much more costly. An added benefit is that the starter battery engine will automatically charge the domestic bank even if the domestic engine generator is not running, this means I can run all navigation and electronics for as long as I want if one engine or generator fails. I'd say that's a safety benefit

 

[PaulGooch]

<snip>

It is still two separate battery banks, that is exactly what the VSR's are designed to make possible, particularly when you only have one generator. The VSR connects the batteries when the voltage goes above 13.8 volts and disengages when it goes under 12.8 which keeps them separate when there is no charge, thus making sure you always have power to start (again provided your batteries are ok and will accept the charge currents)

<snip>

All the time the engine is running, you only have one bank, because as soon as you start the engine, the alternator output will activate the VSR as the alternator output is greater then 13.8 volts. The only time the voltage will drop below 12.8 volts with the engine running is if the alternator fails, because a fully charged battery has a greater voltage than 12.8.

Therefore, if there is a problem with the domestic batteries, they can discharge the engine batteries whilst you are under way.

 

[A_8]

All the time the engine is running, you only have one bank, because as soon as you start the engine, the alternator output will activate the VSR as the alternator output is greater then 13.8 volts. The only time the voltage will drop below 12.8 volts with the engine running is if the alternator fails, because a fully charged battery has a greater voltage than 12.8.

Therefore, if there is a problem with the domestic batteries, they can discharge the engine batteries whilst you are under way.

If your batteries are dead or messed up no charge system will help. I'd say you have bigger problems then the VSR if one battery bank is draining the other as well as a 60Ah+ generator, that bank will explode as long a you keep feeding it 30 amps or more if it does not store it so I suggest you get in the life raft even if you have only one generator and one battery bank.
That aside it is not likely in a situation like that for the voltage to go over 13.8 (or you being able to start the engines in the first place ) as everything will be stressed to the max so the VSR still keeps the batteries separate.

Regarding the 12.8 volts, I can only say that you obviously don't understand how it will work in practice, trust me it will not keep the banks connected for very long. I know, I've used it.

 

[pappaecho]

I may be a bit simple but I dont really understand why the bank should be receiving a 30 amp charge. In my experience an alternator may start at that level to replace the starting current, and then it quickly drops back to a few amps to charge the batteries, according to their voltage relatively to the cut off voltage. The fact that diodes or VSR's are in the circuit should not affect this ...right??