Battery Isolator(blocking diode)

[tome]

[ QUOTE ]
This will drop to 13.8 with a diode fitted. No argument.

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Sorry to be in disagreement with you Boatmike but this is simply not true if you can connect the regulator sense wire downstream of the diode (ie battery sensed alternator).

I don't like relays for current switching applications, so unless stuck with a machine sensed alternator would go for a diode splitter every time.

 

[alahol2]

I've fitted a relay as per Stemar's suggestion and it seems relatively foolproof. A genuine question, what is your objection to the use of a relay to switch the house battery into the charging circuit?

 

[Phoenix of Hamble]

On a related subject..... I have an alternator connected to three batteries via a diode splitter..... and a machine sensed alternator.... clearly I am looking at an Adverc style regulator/controller to improve the charging system, but I also have 2 solar panels and also an Aerogen generator also connected into the 3 batteries (via the appropriate controllers/diodes to ensure no overcharging and drain)....

My question.... if I buy an Adverc, will I need to isolate the other charge sources when the engine is running to ensure correct operation of the alternator controller?

I am guessing here, but wondered if the Adverc unit might detect voltages at the battery that are actually from the wind gen, and consequently drive incorrect activity at the alternator.....

 

[roger]

1,2,both switches

THe cinventional 1,2,both,off switch is fine if you and all members of your crew always carry ourt instructions perfectly. If you ever make a mistake when tired or seasick or drunk you can destroy the alternator. I'm not perfect so I use a system that does not isolate the alternator output from the batteries. I think that a momentary silly mistake will not be fatal
Split diodes and relays also stop you chrging one battery by discharging the other - which could be a problem if one battery dies on you. Its a complex subject as the discussion has indicated and there are no simple answers.
I suggest you buy a cheap digital multimeter and monitor your batteries on and off charge. If your voltage while charging is below say 14 volts then you probably dont have an adequate charge rate.
In any case since you do not expect to run your engine very much you would find it advantageous to fit a smart charger to get the maximum possible charge rate. Sterling alternator regulators cost around £120 a bit better than £200

 

[tome]

Short answer we had to fit our nav systems to 20 jet boats in a remote location. They were fitted with relays and we suffered many failures. To be fair to Halcyon's views, the relays were close to their switching limits and I'm quite sure that he would have chosen a better product. We didn't have any choice.

We could only buy stud diodes, but had our own heatsinks made up and cured the problem by building our own splitters.

My main objection is the arcing of relay contacts when switching high current loads, and the fact that they are wearing out from the day you fit them. A diode is a solid-state device. Provided they don't fail in the first 72 hours (infant mortality) I wouldn't worry too much about their reliability.

 

[tome]

Halcyon is a knowledgeable contact on your query and has a useful website here

My thoughts are that I'd probably want to disable wind and panel charging when running engine, unless all were independently regulated and protected from reverse current in which case I'd connect them together without a second thought.

 

[William_H]

Hi Chris i hope I am not too late for this argument living 8hrs time remote means the fun has often died by the time I get on at 8AM. i often think npeople don't read their posts after the first night qnyway.....
You have 2 batteries so that you can discharge the service battery while retaining a fully charged battery for engine start. you need however to connect these batteries in paralell to charge them from the engine. So with your 4 pos. switch you should run the engine in the both position. Now most people eroneously start in both position. This gives a jump start all the time which is good but it means if one battery has died of old age you won't know it until the other dies. So always or occasionally start on one battery and next time the other battery to ensure both are good for an engine start. (the most demanding job). Once the engine is starteed again you need to switch to both to charge both.
Now when living on board or sailing and you want to use lights etc. you need to be switched to only one battery otherwise you may discharge both batteries and be without an engine start. Then come time to start the engine if it is flat you can switch to the alternate battery or both for a jump start.
This system is fine provided you remember to go to one battery only for sailing and remember to go to both for charging and one for starting. (at least occasionally) this "remember" thing is why voltage sensing relays or diodes are used. it means that you can use only one battery or the other position for your entire voyage without changing the switch. because although only one battery is selected the other will be automatically be connected to the charging source whenever the alternator is charging and will automatically isolate the batteries when not charging. in this case the only time you would ever select both position is if you had a flat battery then tried the other battery and found it also flat and needed to use both batteries at once for a start. by not needed to change the battery switch you eliminate the worry of alternator damage. (Although I think this highly unlikely myself) note as stated diodes if added to a standard system will reduce the voltage to the batteries because of their inherant volt drop and so will reduce the amount of chrge you batteries get. so don't use em.
The other alternative which is what most people do is to always operate in the both position which at least gives you a double capacity battery but does not give true redundancy and isolation.
I reckon that with 10 minutes engine running only you will get pretty much the same amount of charge out of the standard regulator as you have than with a smart charger. no you won't get a full charge. But that probably won't matter so much to you. so the cost of a smart charger is not justified unless you want full charge in minimum engine running time from a flat battery ie if you ran a fridge.
Hope this makes sense. regards olewill

 

[boatmike]

No need to apologise for disagreeing with me old chap! I agree with you actually, and this is a simple solution to the marginal charging voltage drop objected to by others . But as we don't know it's a battery sensed alternator (although it probably is) I was trying to keep the subject simple.
The fact is that diode splitters are now pretty standard on most new boats because it's a foolproof system. The charging rate the battery sees is still acceptable being between 13.8 and 14.1 volts which any textbook on 12 volt electrics will tell you is the desired charging voltage although probably nearer the bottom end as I said originally. A simple expedient such as the one you mentioned overcomes any objection to the use of diode splitters but for those who want more you can fit a smart charger. I would not resort to fitting relays as it is unnecessary. Granted that if you build a big beefy one with low operating resistance they can be OK but I have seen too many that are not and either fail or have higher resistance. (See tomes post) Yours is a better solution than fitting a relay IN MY OPINION!

 

[jollyjacktar]

I have fitted blocking diodes [splitting diodes] in parallel to the four position switch as in your instalation. This has the effect that if the switch is accidentally turned off when the motor is running [assuming it is a diesel] then you will not cook things or whatever, but the charging will continue via the diodes [albeit at a reduced charge rate], further to gain the effect of full charging then the four position switch selection will still select the charging path as charging will follow the circuit of least resistance through the switch.

If you need details, send me a personal with email details and I will forward diagrams etc.

 

[duncan]

I am with you 100% Will; for the use and applications outlined I would stay with what you have and schedule battery changeovers into your normal routine ie. Start on starter and leave connected to replace charge used. Switch over to aux battery when you stop the engine on teh way out. Back to both for starting on the way in and leave charging both until you get back on the mooring. This is how I run mine. I run the engine longer though as I don't have sails! I am also 'fortunate' to have a Lowrance Sonar/Plotter which is set up with a digital Voltage window permenantly on screen (most of their products have it) and I get an idea (but not all the status obviously) of each seperate batteries' condition by checking the voltage when getting on board each time.
I actually switch via 2 seperate keys rather than the 1,1,2,off switch, despite having bought one last year, for exactly the reasons given in some earlier posts - I know I have to have at least one key pointing down with the engine running!
Stick with what you have and use it carefully - you are going to have to deliver some additional charging through the season tooo I suspect.
Have a good season.

 

[rjp]

Is there a simple way of telling if my alternator/regulator is machine sensed or battery sensed if I don't know? If battery sensed and I wanted to fit blocking diodes how easy would it be to sense the voltage downstream of the diodes on a two battery installation?

John

 

[bluedragon]

From what I've read, machine sensed alternators have three connections, battery sensed have four. I believe some machine sensed regulators can be modified, but there are probably others who can better help you with this.

 

[halcyon]

Have you a little wire from the alternator to the battery pos? if so you probably have battery sensing. I f this goes to the battery, or as long as it's between blocking diode and battery your ok.
Why not use a relay ? avoids the the worry.

Brian