Fault finding split charge diodes

[martinriches]

I have two battery's charged through a split charge diode device. Using a multimeter I get continuity between the positive terminals on the battery's. Also testing the diodes I get a voltage drop on the one diode and nothing on the other. Is there something wrong here like a diode not working?

This would enplane why my battery's keep dying.

Martin

 

[sailorman]

Sounds like a diode duff
if so why not fit a VSR
i have the Victron "Cyrix" £70

 

[halcyon]

Does your multimeter have a diode test? if not you can use the resistance setting.

Remove power cables, then set ohms, put red probe on input terminal, black on output terminal, check reading. Now reverse, put black on input terminal red on output. You should have low resistance one way 1000/2000 ohms, and infinate the other way.

If both reading are the same you have a faulty diode.

Brian

 

[martinriches]

Thanks for the reply. I cant' work out the difference between a VSR and a spit charge relay. What are the advantages or disadvantages.

Martin

 

[sailorman]

voltage sensitive relay
I Have One of These

 

[Tranona]

Another alternative is the BEP marine VSR from Merlin on www.power-store.com. Should be straight swap for the diode - just about to do it on my boat after good experience on another boat.

 

[bob234]

Hi Tranona,

What's the advantage of the VSR? Is the diode splitter thingy redundant now? I have had a read and, not being very techy I didn't understand. Sorry

PS Do you need to take the last full stop off your link?

Many thanks,

Bob

 

[halcyon]

[ QUOTE ]
Thanks for the reply. I cant' work out the difference between a VSR and a spit charge relay. What are the advantages or disadvantages.

[/ QUOTE ]


They are the same thing, VSR is just a new techy name.

How does it work, try here this is how a split charge relay system works.

Brian

 

[bob234]

I know you weren't responding to me but - Thanks. At least I now know they are the same thing doing the same thing.

Cheers,

Bob

 

[sailorman]

the diode will drop the alternator voltage as it passes through to the batteries by as much as 0.8v
the VSR will give the batteries full alternator volts so is more efficient

 

[Tranona]

Hi Bob

Yes, remove the final stop - sorry about that!. The advantage of the VSR is that there is no voltage drop. On my Bavaria the master switch is not on the positive and covers both banks. So I am replacing with a BEP switch cluster with a separate switch for each bank and a parallel. The panel with have the three switches in line will be installed through the bulkhead of the locker where the batteries are. The VSR is a separate unit and will replace the diode on the bulkhead in the engine bay.

Hope this helps

 

[earlybird]

There are many posts about diodes and their attendant voltage drop, and frequent references to VSR's. I've fitted an X-split to my last two boats, no voltage drop and no trouble. Can recommend them.

 

[yoda]

Martin

It certainly sounds like you have a defective diode. Before making a change to your charging system you need to understand the full setup otherwise guidance given by others may not be entirely accurate. It is true that diodes drop the voltage by about .8v which if used in conjunction with a standard alternator can be a problem however when used in conjucnction with a battery sensed alternator controller is fine. As has been said by others there are alternatives which get round the voltage drop issue if that is what you want to do. First thing to do if you want accurate advice is to describe the setup fully so others can understand the full extent of the system. Hope that helps.

yoda

 

[William_H]

A diode is very much likea non return valve in a water or hydraulic system. It automatically allows current to flow in one direction only. So we fit one diode between the charging source and the first battery and another from the charging source to the 2nd battery. Now for current to flow from one battery to the other requires the current to flow through 2 diodes (non return valves in the blocking direction. So it can't hence batteries are charged but isolated.
Now just asa non return valve has a spring which must be overcome to allow fluid to flow so the diode has a band of electrons which must be overcome. For silicon this requires .7 volt to get any current to flow and will always drop that voltage or more when conducting. To get a battery charged properly you need at least 14 volts tot he battery terminals. Most standard alternators are regulated to generate 14 volts. So .7 volt lost ina diode means poor charging. You can sometimes increase the voltage of the alternator by adjustment or by moving the wire that senses the product of the alternator from the alterrnator output to the battery itself. (So alternator is regulated to 14v at the battery or 14.7 at the output of the alternator. This can be difficult on simp[le car alternato /regulator.

The diode is usually very cheap reliable and simple.

A Voltage sensing relay is essentially a switch. Contacts connect to hard wiree the batteries both to the alternator so they both get charged. The trick is that the second battery is only switched to the first battery (alternator) when the alternator is charging and the first battery voltage rises to about 13volts. When the engine is stopped the voltage of both batteries falls to about 12.5 and this factt is sensed and the switch (relay) is opened to provide isolation. So no voltage dropped. Hence no complications or poor charging.

If you can't measure a voltage drop or resistance of one of the pair of diodes ie it shows zero ohms then it must be shorted. It will probably show zero ohms in both directions. Hence isolation is lost between systems. One system ir domestic will be able to drain both domestic and engine battery or the engine will be started on both domestic and engine battery. However I suggest that diodes are reliable and it is possible that you are not testing correctly or there is wiring connected to the diodes which effectively bypasses the diodes. So disconnect wires from at least 2 terminals of the diodes.

A multimeter uses quite small currents when measuring resistance hence small voltage drops so when your diode drops .7 volt it shows up as a large resistance in thousands of ohms. Don't be dismayed this is not the real resistance of the diode which is quite low once the barrier .7volt is overcome. You can perhaps more realistically check the diodes witha battery and lamp. So current form the common terminal + through the diodes to eitherr one terminal or the other. Both should conduct and both should not conduct with battery or wiring reversed.
I hope that explains more clearly the difference between diode and VSR olewill

 

[sailorman]

the "Cyrix" is good because it senses both battery banks all the time & opperates in conjunction with any "Charge Source"

 

[bob234]

Thanks Tranona. They are slightly different in terms of voltage drop then.

Cheers,

Bob

 

[halcyon]

[ QUOTE ]
Thanks Tranona. They are slightly different in terms of voltage drop then.

[/ QUOTE ]

That slight difference can make a very big difference in the recharge level of your batteries.

Brian

 

[martinriches]

olewill

Thanks for the detailed explanation.
you may be right in saying I didn't test the diode correctly. I will have another go next week. A VSR sounds like a good idea anyway and I think I will fit one as there are not very expensive.

Martin

 

[martinriches]

Sailorman

Thanks for the [Cyrix] recommendation. I have just ordered one.

Martin

 

[sailorman]

Good choice
if you have the 1,2,both isolator switch you really dont need the "couple both" wire wired up on the cyrix.
i wired the neg of mine to my batt neg switch so that the cyrix is isolated when not i am not on board. i never leave my battery charger on when i leave the boat after a w/e .

ps use the bolted connections NOT the spade connectors