Self Blocking Diode or VSR?

[NormanS]

My charging system has, what I presume, is a conventional arrangement with a charge splitting diode which favours the starting battery.

The only demand from the starting battery is to start the engine, and to run the engine "room" fan.

This means that when I am lifting the anchor, with the electric winch, and thereby putting a huge drain on the service bank, the alternator is busy charging the engine starting battery. This can cause a temporary low voltage, which my plotter doesn't like.

I also believe that using a diode means that I am depriving the service batteries of about 0.5 volts, which means that they are probably never being completely charged.

Would I be better changing to a Voltage Sensitive Relay, and if so, what does this involve?

Please if you are going to give me advice on this, keep it very simple, as my understanding of electricity is quite limited.

 

[Billjratt]

the diodes don't "favour" either battery, they simply split the power in a manner that doesn't allow the batteries to drain each other should one be down.
When you're hauling chain, the alternator will be feeding the side that needs it most (the domestic bank - as it's voltage will be lower than the starter battery.)
The lost voltage across the diodes, will, as you say, reduce the charge.
A 1-both-2-off switch or a relay could be a cure, but better to boost the charge to cover the loss, by 'fooling' the alternator. A smart charger like sterling or adverc will do the biz for you, and 'fill' the batteries properly.

 

[VicS]

A diode splitter does not specifically favour one battery over another. The least charged will tend to automatically get the lion's share of the alternator output.

A VSR does favour one battery over the other. Normally wired to give priority to the starter battery switching in the domestic battery when the volts have risen to some predetermined level.


You are right about the voltage drop ... may even be as much as 0.7( rising with increasing current). A vsr does not suffer from this voltage drop.

From what you say I wonder if you do already have a VSR ??
Even if you do not then fitting one in the normal way will make your problem worse not solve it. It could be fitted to give priority to the domestic battery but that would mean your engine battery not recharging immediately.

Your problem may only be solved by fitting a separate battery for the winch. That can be charged via a VSR from the supply to the domestic battery. A dedicated winch battery could be located close to the winch eliminating long cable runs carrying high currents

 

[Chris_Robb]

A diode splitter does not specifically favour one battery over another. The least charged will tend to automatically get the lion's share of the alternator output.

A VSR does favour one battery over the other. Normally wired to give priority to the starter battery switching in the domestic battery when the volts have risen to some predetermined level.


You are right about the voltage drop ... may even be as much as 0.7( rising with increasing current). A vsr does not suffer from this voltage drop.

From what you say I wonder if you do already have a VSR ??
Even if you do not then fitting one in the normal way will make your problem worse not solve it. It could be fitted to give priority to the domestic battery but that would mean your engine battery not recharging immediately.

Your problem may only be solved by fitting a separate battery for the winch. That can be charged via a VSR from the supply to the domestic battery. A dedicated winch battery could be located close to the winch eliminating long cable runs carrying high currents

One other thought, which is causing the low voltages on the domestics, whilst using the winch. You may actually have bad connections which allow normal amps through, but once you start pulling major amps, it may not be man enough. Check all the connections, and do a check for voltage drop on the wires at the alternator and the battery end - and see what the drop is. I had a problem which manifested itself just like this. I Replaced a perfectly good battery before realising what the problem was. Do you have a digital multimeter? If not go and get one, invaluable.

 

[boatmike]

My charging system has, what I presume, is a conventional arrangement with a charge splitting diode which favours the starting battery.

The only demand from the starting battery is to start the engine, and to run the engine "room" fan.

This means that when I am lifting the anchor, with the electric winch, and thereby putting a huge drain on the service bank, the alternator is busy charging the engine starting battery. This can cause a temporary low voltage, which my plotter doesn't like.

I also believe that using a diode means that I am depriving the service batteries of about 0.5 volts, which means that they are probably never being completely charged.

Would I be better changing to a Voltage Sensitive Relay, and if so, what does this involve?

Please if you are going to give me advice on this, keep it very simple, as my understanding of electricity is quite limited.

I don't disagree with previous posts. A VCR won't give voltage drop but a diode splitter will. However if your sensing wire from the alternator is direct to the battery and is "battery sensed" not "machine sensed" which most are, then the alternator will increase its voltage accordingly to give the full charge voltage to the battery being sensed. If a smart charger, like a sterling is fitted it will do even better and give full amperage charge and adjust voltage again to the battery being sensed. Most setups make the service battery the one being sensed as these are usually the ones that get deeply discharged. With a diode splitter this will not result in your starter battery being overcharged and is the setup I favour myself although opinions on this will differ. If therefore you have a diode splitter already the best plan may be to invest in a smart charger rather than changing to a VCR.

 

[john_morris_uk]

I don't disagree with previous posts. A VCR won't give voltage drop but a diode splitter will. However if your sensing wire from the alternator is direct to the battery and is "battery sensed" not "machine sensed" which most are, then the alternator will increase its voltage accordingly to give the full charge voltage to the battery being sensed. If a smart charger, like a sterling is fitted it will do even better and give full amperage charge and adjust voltage again to the battery being sensed. Most setups make the service battery the one being sensed as these are usually the ones that get deeply discharged. With a diode splitter this will not result in your starter battery being overcharged and is the setup I favour myself although opinions on this will differ. If therefore you have a diode splitter already the best plan may be to invest in a smart charger rather than changing to a VCR.

I agree and its the system that we use. Having said that, if either a VSR relay of a split diode with battery sensing is fitted correctly its six and two three's as to which is best.

If the engine is running and the domestic batteries are being pulled down (to upset the plotter) by the load of the windlass, there is something wrong somewhere. Faulty wiring, loose/dirty connection or a faulty battery that is gaining a high internal resistance would all be possible causes.

 

[halcyon]

Would I be better changing to a Voltage Sensitive Relay, and if so, what does this involve?QUOTE]

It depends on your current system, you will have to sort out if you have diodes or a VSR.

The diode system will not prioritise your engine battery, the alternator output will take the least line of resistance, in your case, with the winch running, it will be this circuit. So you will need to check voltages to see were, or if there is a volt drop in the winch circuit.

You can lose 0.5 to 1.2 volt through a power diode, depending if it is carrying full load or not, and what type. You can fool the alternator to maintain the voltage to the service battery, and avoid this drop.
But there is now a argument that in doing this you are overcharging the engine battery.
Because the volt drop across the service diode could be 1 volt, the drop across the engine diode ( low current ) could be 0.5 volt, thus the service battery is 14,4 volt, the engine battery is at 14.9 volt.
discuss

If you have a VSR it will, or should cut in quickly after starting, but it may drop out with the winch running, in which case you would see the voltage going up and down.

So to do what you want with a VSR you need to interface it to the winch solenoid, so with the winch running it will hold in the relay. By-passing the drop-out function for a limited time.
The reason the VSR drops out at a minimum charge voltage is to protect the engine battery, and also to protect the charge circuit from excessive current drain, and possible damage to cable from high current.

But the first job is to identify what system you have, what your problem is, then it is possible to work out a answer to solve it.

Brian

 

[VicS]

But the first job is to identify what system you have

To which end it may be necessary to be able to distinguish between a diode splitter and a VSR by looking at them.

Now a diode splitter will have three heavy terminals. The alternator will be connected to one and the battery banks will be connected to the other two.

I think I am right in saying that a VSR will only have two heavy terminals. One will connected to the alternator and the starter battery. The other will be connected to the house battery. A VSR will also have a negative connection.

Just to make life interesting of course other devices are possible such as an X-split (in essence an electronic VSR) or even something like one of Sterling's alternator to battery chargers.

Poor old NormanS. He said, "Please if you are going to give me advice on this, keep it very simple, as my understanding of electricity is quite limited."

 

[halcyon]

To which end it may be necessary to be able to distinguish between a diode splitter and a VSR by looking at them.

Poor old NormanS. He said, "Please if you are going to give me advice on this, keep it very simple, as my understanding of electricity is quite limited."

That's why I but the bottom line in Vic.

It would be a good to start with a simple question, what make and type of boat.

Your discription of a VSR may be over simplified, we have supplied 1000's with 2 or 3 big bolts, 3 small pins and 6 or 8 pin socket. Boat type will answer this one.

Think the answer may be to start with alternator voltage and battery voltage, splitter may be hidden somewhere.


Brian

 

[NormanS]

Thank you all very much for your helpful and considered replies.
I do have an Adverc system
I now wonder whether I have a diode splitter or a VSR. It certainly has three heavy terminals.
You're right Vic, I am struggling with some of this, but you have all given me helpful pointers.
I'm off sailing tomorrow for our final cruise of the season, with lift-out in ten days, so I'll check up on the points raised, but leave any alterations until laid up.
Thanks again, Norman.

 

[halcyon]

I'm off sailing tomorrow for our final cruise of the season, with lift-out in ten days, so I'll check up on the points raised, but leave any alterations until laid up.
Thanks again, Norman.

Sounds like diodes, but before you lift out can you take some voltage readings.

That is at the batteries with engine running, and at winch when you are using it.

Once you are out of the water it may be very difficult, and it is all assumption then.

Brian

 

[NormanS]

Halcyon.
Boat is a Cromarty 36 built in 1991 by Blondecell, (alas no longer with us), fitted with a Volvo MD22. i.e. a Perkins Prima with an expensive green paint job. I will check voltages as suggested with my multi-meter. The splitter / VSR is quite accessible. I've just always assumed that it is a diode.
Thanks.

 

[halcyon]

Halcyon.
Boat is a Cromarty 36 built in 1991 by Blondecell, (alas no longer with us), fitted with a Volvo MD22. i.e. a Perkins Prima with an expensive green paint job. I will check voltages as suggested with my multi-meter. The splitter / VSR is quite accessible. I've just always assumed that it is a diode.
Thanks.

It will help as to why you have low voltage for the winch, as from what you have said you should be ok.

You should have around 14 + volt with the engine running with revs on, depending on winch rating / alternator size, it could drop a lot lower with winch engaged.


Brian