Blocking diode

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Morpheous

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My old sunseeker wiring diagram (kindly supplied by forumite) shows a blocking diode between battery charger and engine batteries. While investigating a problem with my new battery charger I discovered that I still read a small voltage - about 2 volts - on the engine batteries terminal of the battery charger.

Is this normal? Battery charger manufacturer said that the charger has internal diodes and does not need separate protection and my diode will cause a voltage drop. The implication being that it could just be removed. Is this correct or sensible?

Thanks in advance
 
If the new battery charger has an internal diode, it would be both correct and sensible (actually, advisable) to remove the old diode. Diodes do indeed cause a voltage drop, the internal one will have been factored into the build specs of the charger, any further external ones will not, and will cause a drop in volts.
 
A silicon diode will drop 0.6V with pretty much no current through it. As you take more current the voltage drop will rise. It could explain your observation, but 1.5V to 2V drop is high. You may have resistive drops in your wiring too.

As the other poster said, if the charger is designed to not need the external diode then remove it.
 
WhiteMischief said:
Interesting, I wonder if this explains why my voltmeters read about 12-13 volts but the output from alternators is 14.5 or something.
Click to expand...

Most likely a different issue. A blocking diode between the mains charger and engine battery will have no effect on the volt meter reading with regards to alternator output. Unless of course the blocking diode is between the battery and both charging sources. With no charging going into the battery, it should read around 12.6 volts (fully charged), rising to something around 13.8v to 14.4v depending on the charger. Bear in mind, cheap volt meters are not always hugely accurate, mains charger outputs vary and alternator output my be 13.8v to 14.4v, so figures will vary.

It is possible that you could have a split charge system incorporating a spit charge diode, this would cause a voltage drop between the diode and the batteries. Wired correctly it should not cause a volt drop with the mains charger though. To charge two battery banks via a mains charger, the charger should be capable of independently charging the banks and should be wired in AFTER a split charge diode.

Some details of your charging/wiring system, new charger make/model would help with a better informed answer. A peek at the wiring diagram would help too, PM me and i'll give you my email address, if you'd like me to give it a quick look over.
 
According to the diagram, the original charger has only two outputs and you have three battery banks. One bank for each engine and one for the domestic/electronics circuits (a bank being one or any number of batteries wired in parallel).

Which charger have you bought now ?
 
I think this is the wiring for the standard build. Mine always had 4 batteries in 2 banks as far as i know. It looks like the 3rd may be to do with a generator set up, but mine hasn't got a generator sadly.

The last battery charger was a Waeco mobitronic that was installed in abount 2003, not sure what was there before that. I have just put in a Stirling pro charge D digital 30 amp (1230CED). This has 3 outputs, I'm only using 2 and have connected output 2 & 3 together as per the instructions.
 
The wiring diagram shows one battery for each engine and one for the domestic circuits. The optional generator has a fourth battery, that would be solely charged by the generator itself and is wired into the shore power circuit. The mains charger in the diagram only has two outlets, so a blocking diode was fitted between one outlet and the two engine batteries, to keep them isolated from one another.

If you only have two banks, there would have been no need to fit a blocking diode. So check to be sure how many banks you have, three banks will have three isolator switches, according to the diagram. Irrespective of the number of banks, check for the presence of and remove if found, a blocking diode on the mains charger circuit. Your current charger is capable of charging two or three banks, so no need for the diode even if you find you have three banks.
 
Ok I think I'm getting confused now!

I have 3 isolator switches:
Port Engine
Stbd Engine
Domestic

I have 4 batteries, 1 for each engine & 2 domestics ( I think)
Definitely haven't got a genny. But would like one.

The old charger only had 2 outlets - is this why it needed the diode - to isolate the engine batteries?

Should I now remove the diode and connect each engine battery to a dedicated output on the charger?
 
WhiteMischief said:
Ok I think I'm getting confused now!

I have 3 isolator switches:
Port Engine
Stbd Engine
Domestic

I have 4 batteries, 1 for each engine & 2 domestics ( I think)
Definitely haven't got a genny. But would like one.

The old charger only had 2 outlets - is this why it needed the diode - to isolate the engine batteries?

Should I now remove the diode and connect each engine battery to a dedicated output on the charger?
Click to expand...

You're getting confused, you said you had four batteries in two banks a couple of posts ago :D

Right, three isolator switches should mean three banks. Remember, a bank can be a single battery or any number of batteries.

The old charger only had 2 outlets - is this why it needed the diode - to isolate the engine batteries?
Click to expand...

That's right, to a point, it's most likely there for the alternator that charges the engine batteries too. But, you have a three output charger now, so you can (should) wire the mains charger AFTER the diode.

<EDUCATED GUESS MODE ON>

Previous system would have been :

One alternator and one charger output to the domestic circuits.

Other alternator and second mains charger output to the diode input. From the diode outputs to the two engine batteries. Therefore, each engine battery is kept independent.

Only other way would have been to have had two diodes fitted, which would make no sense.

<EDUCATED GUESS MODE OFF>

So, you just need to double check that the alternator on one engine is wired to the diode, in which case the diode stays put. What you then do, is to use two outputs from the mains charger to the two engine battery banks. You can connect these to either, the output terminals of the diode, the battery terminals, or the battery side of the isolator switches, whichever is easier for you.
 
Confusion partially clearing! I now understand what you mean by banks now!

Your educated guess looks pretty consistent with what I have seen. I have also found some handwritten notes from a former owner that I'm just scanning now which I think shows how the alternators are connected. Hopefully it will be readable, will email over shortly.

If the diode needs to stay I may consider replacing it because I definitely get voltage albeit small on the outlet that is currently driving both engine banks. Presumably this must be coming from the diode unless there some dodgy wiring in there somewhere.
 
If the previous owners diagram is correct, that's a pants charging system, sorry.

The 240v charger is easy to sort, run one output to each bank, connecting to either the batteries or the isolators, the diode is totally redundant then. You'll then be operating as you have always done, except for the small volt drop on the shore power caused by the diode. Job done as far as fitting the new mains charger goes.

Not quite sure how the "changeover switch at dashboard" bit operates. what exactly do you have to do here ? It looks to be connecting all three banks in parallel to get the domestic bank charged. Not a good idea.

The alternator charging looks a mess to be honest and i'd look at making some changes. It looks as though you have to fiddle with switches to get the alternators to charge the domestic batteries, you are using two whole batteries just to start the engine and the alternators are mostly just charging the engine batteries.

Personally, i'd only have one bank to start the engines. If a single battery will start one engine, i see no reason for it not to start both engines. It's OK thinking that you have twin batteries, so if one goes flat the other engine will start, but it still leaves you limping on one engine.

Options :

1) One battery to start both engines.
2) The other three in a single bank for domestics.
3) Port alternator connected to each bank via a diode (2 output model)
4) Stb alternator connected to each bank via a diode (2 output model)
5) You'll be left with a spare isolator, connect this to the other two isolators to parallel the two banks in the event of a flat engine battery, thus starting the engines from the domestic bank.

This system would be my personal choice. It gives you maximum battery Ah for the domestic circuits and the charging will go wherever it's needed most, with no user intervention. It also gives you a way to start both engines in the event of a flat engine battery. Easy to wire, basically, just take the short charging cable from each starter to each alternator out, run a cable from each alternator to a diode and then from the diode to each bank. One battery cable would need taking off of it's isolator and re-routing to the other starter.

Or

1) Leave the batteries as they are.
2) Port alternator connected to each bank via a diode (3 output model)
3) Stb alternator connected to each bank via a diode (3 output model)

Not quite as nice as the above method, but would involve less cable routing for you. Leave all the main battery cables as they are. Take the short charging cable from each starter to each alternator out, run a cable from each alternator to a diode and then from the diode to each bank.

If you decide you want to upgrade the alternator charging, i can give you some more details, or you could get a local fitter to do it for you. Shouldn't need to sell any internal organs to pay him. :D
 
Thanks for all your efforts on this Paul.

I strongly suspect the former owners diagram is not quite right! More on this below.

On the dash I have a crossover switch. This is to be used if one engine won't start you flick it (its just a spring loaded switch there is no left or right) and switches to the other battery. I believe it would for example try to start the port engine from the starboard battery. It's only there if one engine battery goes flat.

I'm pretty sure that the port alternator always charges the port engine battery and stbd does the stbd. The stbd alternator failed last year and it was definitely the stbd engine that got lazy starting.

The alternators also charge the domestic batteries without switching anything over. The former owner told me that if we left the fridge on just battery power they would go flat in hours. We have had it on all day when we have been running and have never flattened any batteries.

What could be happening here according to the diagram is that the crossover switch would let me start the engines from the domestic batteries? I think the crossover switch may be connected to an solenoid that is at the top right of the original Sunseeker wiring diagram. I think the crossover switch could be labelled as 'parrallel control' on the left hand diagram.

So in the short term (if I understand this correctly) provided the alternators are connected to the switched side of the isolators and therefore isolating each bank I can then remove the diode, use all 3 outputs of the charger.

I then need to verify what the crossover switch does and check that the domestic batteries are being charged by the engines. If not then I will have to look at sorting it. I suspect they are though cos I'm sure we would have flattened by now if they weren't.

I'll stick a beer in the fridge for you :)
 
Having had another look at all the diagrams and bearing in mind your last post, i'd ignore the previous owners digram. It didn't make a lot of sense.

I see the "change over" switch is actually the parallel switch, as you say. The handwritten diagram mistakenly shows this to be involved in the charging circuits. The Sunseeker diagram shows no alternator circuits, which kind of brings me back to my "educated guess" a few posts ago lol

Two alternators cannot independently charge three battery banks without something like a diode. Could be a relay, but highly unlikely, as you have a diode :) So, i would again suspect that one alternator goes straight to the domestic circuit and the other goes to the diode input, the old mains charger also went to the diode input, then the two diode outputs went to the two engine batteries. You must check where the alternator outputs are wired to be sure. If one does go to the diode, you simply need to connect two of the mains charger outputs to the two diode outputs, job done. Mains charging will be direct, no volt loss, alternator charging will be via the diode, slight loss but no big deal, it's always been like it.

According to the Sunseeker diagram, the voltmeter is wired to the Stb engine battery, which also runs a fair bit of other stuff too. So your voltage will show a touch lower than you might expect, as it'll reflect the voltage drop caused by the diode. When you've wired the mains charger after the diode, you should see a slightly higher voltage when you turn the mains charger on.
 
There is definitely only one input on the splitter diode exactly as per the diagram. Its mounted just above the charger, which feeds straight into the diode and then the 2 outputs got to the isolator switches. There does appear to be 2 solenoids though, but maybe they are relays in disguise?

It would be intresting to establish which of the alternators charges the domestic batteries so that I know which engine to run to charge them if I ever need to. Can one alternator not be connected directly to 2 batteries then?
 
WhiteMischief said:
There is definitely only one input on the splitter diode exactly as per the diagram. Its mounted just above the charger, which feeds straight into the diode and then the 2 outputs got to the isolator switches. There does appear to be 2 solenoids though, but maybe they are relays in disguise?
Click to expand...

Ah, well that makes that part of the exercise simple then. Take the relay and and connect two of the charger outputs to what were the diode outputs, job done. Anybodies guess with the solenoids/relays.

It would be interesting to establish which of the alternators charges the domestic batteries so that I know which engine to run to charge them if I ever need to. Can one alternator not be connected directly to 2 batteries then?
Click to expand...

If one alternator was to be connected to two batteries, it would then make those two batteries a bank. Very bad way to wire them, if one went flat and you tried starting the engine from it, it would try to draw the full engine starting current from the charged battery, through the charging cable and most likely melt it.

You have some electrics running from the Stb engine battery too, looks like everything from the console panel, which looks pretty much like stuff you'd only use underway. The port battery is solely for starting the port engine. Given the Stb engine is running some electrics as well as the engine, they may have decided to have the Stb alternator charging the Stb engine battery and the port alternator charging the port engine battery and the domestics. Although the loads on the Stb battery are light, so it would have made more sense (to me) to have wired it so that one alternator charged both engine batteries and the other did the domestics bank. Hard to guess how they decided to do it though.

Personally, i'd have two, three output diodes, so that each alternator charged all three banks. The losses from starting the engine would very quickly be replaced and then both alternators would be charging the domestic bank. With a couple of advanced alternator regulators if needed (doubtful they would be needed). Given that you've never had a flat battery though, it's obvious the charging is up to your needs, so likely best left alone.

Leave the shore charger switched off for a while, with the fridge etc turned on and allow the batteries to partially discharge. Turn all the cabin lights on (not cockpit lights, they work from the Stb battery) and start an engine, the one that makes the cabin lights brighter is the one charging the domestic bank.
 
PaulGooch said:
If one alternator was to be connected to two batteries, it would then make those two batteries a bank. Very bad way to wire them, if one went flat and you tried starting the engine from it, it would try to draw the full engine starting current from the charged battery, through the charging cable and most likely melt it. .
Click to expand...

No I meant for the domestic batteries, could 1 alternator be charging both the domestic batteries.

I like your lights dimming tip - I hadn't thought of that!

Apparently we are going fishing tomorrow, my daughter for the first time this year has expressed an interest to go out and she wants go fishing. Hopefully I can persuade her to help with some wiring first!
 
WhiteMischief said:
No I meant for the domestic batteries, could 1 alternator be charging both the domestic batteries.
Click to expand...

Yes, one charging the domestics and the other doing the two engine batteries via a diode or relay.

Apparently we are going fishing tomorrow, my daughter for the first time this year has expressed an interest to go out and she wants go fishing. Hopefully I can persuade her to help with some wiring first!
Click to expand...

Don't tell her about the wiring until she's onboard :)
 
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