Diode v VSR

Impaler

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I'd like to install a 2nd battery for domestic use and a split charge system. Now is it to be diodes which some say drop voltage or should it be Voltage Sensitive Relays? Websites & salesmen will never agree, anyone got simple advice for a simple non electricially minded sailor?
 

sailorman

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i have used both systems
present boat has vsr fitted presumably from new. originally the engine battery had priority & was totally dedicated engine start. i have fitted a change-over switch to allow more flexibility. the system works fine i have 7 yr old batteries std alternator (70 amp i think). i have used alternator controllers on previous boats with blown alternators resulting so don't plan on fitting another. (others will disagree)
 

john_morris_uk

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Either system is fine just so long as if you use a diode splitter you have wired the alternator to sense the battery voltage and not the alternator output voltage.

And to comment on t'other answer you have had, I have used alternator controllers on lots of boats and have never blown an alternator up yet. I wouldn't like to go cruising without one fitted.
 

Birdseye

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my previous boat had a good system using a relay, but not voltage sensitive. Simply a 30 amp relay wired into the ignition system so that the positive feed from alternator to the domestic battery was only connected when the engine was running. Otherwise, there was no connection at all between the starter battery and the domestic circuits.

No voltage drop so no need for a booster type charge controller. Standard car spares compnents so cheap.
 

Bergman

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Birdseye gives the clue

"Spares are cheap"

The relay system has moving bits of metal - which can break or bend.

Springs that can lose tension

Metallic contacts which can get dirty.

A diode is one solid lump of silicon -

Nothing to go wrong - No moving parts - Nothing to break

Of course its entirely up to you
 

john_morris_uk

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[ QUOTE ]
No voltage drop so no need for a booster type charge controller. Standard car spares compnents so cheap.

[/ QUOTE ]

There seems to be a misunderstanding regarding the function of 'booster type controllers here.

An Adverc/Sterling etc controller if it is working correctly minimises the time that you need to spend charging. A standard 'car type' alternator controller never charges the batteries to anywhere near their capacity. An advanced alternator controller can sense the battery voltage and thereby overcome the voltage drop through diodes, but this is really a SIDE BENEFIT of what the system is doing. Some standard alternator controllers can be wired as 'battery sense' devices, but they still won't charge the batteries very effectively.

The higher charging currents achieved with advanced controllers mean that standard car relays are often not good enough for the role of charge sharing relays in such systems.

You might get away with a standard car part if you have an ordinary alternator controller, but beware of the current requirements and limitations.

Personally my feeling is that diodes don't have moving parts and don't usually fail.
 

VicS

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[ QUOTE ]
if you use a diode splitter you have wired the alternator to sense the battery voltage and not the alternator output voltage.

[/ QUOTE ] But which battery do you sense, the starter battery or the domestics battery?

Or do you modify the alternator by adding suitably rated diode in the internal sensing circuit to boost its output by 0.6 or 0.7 volts.

Or do you buy a diode splitter that has an extra diode to connect the sensing to.
 

bluedragon

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Except that if diodes are fitted, then battery sensing is a MUST. For many standard alternators this means a Sterling or similar unit. Also, even with one of these, the alternator is being driven to a higher voltage than it needs to, to overcome the diode voltage drop. Now, I don't know if this is an issue or not, but I'm sure somebody will. I've gone back to individual isolator switches which give me a) B1 on b) B2 on c) both on. This also means I can use battery 2 to start the engine if I wish. If a relay is used, then fit one with a much higher current rating than the max. alternator output in my opinion and/or go for one specd. for marine use.
 

rhumlady

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I run my setup with split charge diodes for charging and an off,1,2,both switch for selecting which battery to use for engine starting. I have a Stirling regulator controller/booster which senses the battery voltage from the service bank and as the charge is going through the Diodes the float voltage of 14V is dropper to 13.3 at the batteries so avoiding cooking them when on long motoring trips. I have never had a problem with overcharging the Engine starter battery and it is 12 vears old. I agree that the automotive regulators fitted to alternators does not charge the batteries fully.
 
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You can answer your first question by answering a second.

Do you want to add a digital alternator controller to improve your charging regime?

If yes, then go for a diode. These require the controller to get over the voltage drop of the diode, and the controller also requires the diode to allow it to float at a reasonable voltage (as we discovered in Lemain's thread)

If no, then go for a VSR or maybe just a good old fashioned 1-2-both selector switch.
 

qetoo

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I use a device called the Heart Echo Charge. The alternator is wired directly to the domestic battery bank. The Heart Echo Charge gets power off of the domestic batterty/alternator and the start battery gets charged from the Heart Echo Charge. I previously used a VSR, but it had the disadvantage of not dropping out when shore power was connected due to the battery charger holding up the voltage. I've had the Heart Echo Charge installed for five years now. Works great.

I have posted my wiring diagram at:

http://carlten.tripod.com/Electrical_system/electrical.html
 
A

Anonymous

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Welcome to the forum /forums/images/graemlins/smile.gif You might have seen a couple of threads discussing these issues right now. It is difficult to answer adequately without knowing what sort of use you make of your boat, and whether it is left in a marina with shore power and a decent marine battery charger most nights. If you are a marina boat, without a lot of electrics, and seldom overnight at anchor or on a buoy then either a diode splitter or a VSR, or just switch the two batteries in parallel, no problems.

At the top of the range I am now convinced that the answer is to fit a Balmar alternator with a Balmar advanced regulator. There seems to be nothing else on the market that comes anywhere near the performance. In which case, follow the Balmar recommendations for wiring - i.e. diode, VSR or whatever.

Others have discussed the in-between options. Personally I have a bit of a hate on for the 'boosters' - Sterling, Adverc and Merlin. If one is going to spend all that money why not go a little further and get a Balmar?
 

Niord

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Have you tried the X-Split from Driftgate 2000.(adverts in PBO & YM) It is a zero loss diode splitter? I had one on my last boat for 10 years with no problems. A VSR will connect your very depleted domestic battery to the nearly fully charged engine battery as sonn as the engne is started. With a large domestic bank and a much smaller engine battery this could reduce the charge on the engine battery significantly
 

halcyon

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But if you have a fully charged engine battery why do you want a big charge to it, you want the charge to service battery. Another concideration is that with a VSR the alternator is always connected to the engine battery, any fault with the VSR will not loose charge to the engine battery. With blocking diodes and Mosfet systems, were the alternator output goes through a splitter, a fault can loose charge to, or produce a short circiut path between batteries.

Brian
 

Impaler

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Thanks to you all....my head is whirling with unfamiliar terms, maybe I should go back to oil lamps, sextant and lead line! I really know little about electrics but these threads have given me food for thought and I have an idea what I shoul be looking at now. The forum is really good packed with useful snippets. Thanks all.
 

William_H

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Let me try to explain in simple terms. You want a separate domestic battery so it can be discharged without concern for engine starting.
If that is not a concern you don't need another battery.
If you have seperate battery system you need to charge it. Shore power solar are all options but the easiest is to use the engine charging system. To do that you simply connect the domestic battery in paralell with the engine battery.
Now the problem is if you leave it connected then when you discharge the battery using lights etc overnight you will also discharge the engine battery. It will take longer of course because you have 2 batteries to discharge.

So the simple answer is to have a switch which connects the domestic battery to the engine battery when charging and you switch off when not charging. Simple provided you remember to switch on and off again at the right times.

A relay is a switch operated by an electromagnet. It operates whn you connect power to the coil. So if a relay is connected into the "ignition" switch" then it will connect the battery when the engine is on and disconnect when the ignition is off. fine?...no

This system always connects the dommestic battery before starting. A very dead domestic battery can reduce the charge of the engine battery or slow down the cranking. On the other hand a good domestic battery can aid the engine starting especially if the engine battery is tired. You will need a high current switch to carry the starter current without melting. This method is common using the 1,2,both switch however....
The other down side to this arrangement of starting using both batteries is that if the engine battery dies of old age you may not be aware because the other battery makes up for the shortcomings. So you are back to one battery sytem.

So you need a relay that operates to paralell the batteries only when the engine has started. This can be done by connecting to an opil pressure light circuit. Tricky cos the light is on with no oil pressure and you want the relay on with oil pressure.

The simplest in wiring terms is to accurately sense when the engine battery voltage has risen because it is being charged. The VSR. Depending on the actual voltage actuation setting they operate when the engine battery has recovered charge from the engine start usually a few seconds beforte the domestic battery gets a charge as well. This voltage of the engine battery falls a little after engine stop and this is enough to tell the relay to release.
If you have a VSR then carry an emergency jump lead for starting the engine using both batteries. The negatives of both batteries should be connected permanently by a heavy lead
Diodes ? that is another story
good luck olewill
 

Impaler

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Thanks William, I think I'll go for one of the Merlin VSR switch clusters they seem to provide the best of both worlds. It looks easy enough to wire in.
 
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