split charge relay wiring woes

[pvb]

I had though the relay may be the wrong type, I had this along with the spare I tried hanging around for a while so unsure of the specs, didnt realise there were so many types until recently. I will see what else I have.
I have also changed the warning light bulbs for 4 watt versions as the originals were only 1.2v & thought they may have been part of the problem being underpowered, according to my book they should be between 2&4w?
they are also producing a v slight glow when up & running.

I see you describe the relay as a "basic 30A relay". This obviously won't be suitable if your alternator is rated much higher than 30A.

As it seems the electrics on your boat are somewhat suspect, you might be better off getting a marine electrician to check them out.

 

[richievtu]

Ok, attatched is an image of what I believe is the original relay on the boat, lucas srb146, its completely disconnected & I didnt find it until after I fitted the new one, assuming I can test its working would it be suitable for the job & if so I could someone confirm how it is wired up?
thanks again!

 

[VicS]

No it is still not the right type. It is a "change over" relay.

It could be used but I expect it will still operate at a voltage lower than required.

http://www.autoelectricsupplies.co.uk/product/729

SRB 630 would be a suitable type ... ignore the connection for a fridge ( unless you have a fridge)

http://www.autoelectricsupplies.co.uk/product/824


Frankly controlling the split charging in this way from the warning light circuit is an obsolete method. I appears that some modern alternators will not even support the method.

I'd suggest you move on from it and charge the second battery via a voltage sensitive relay ( VSR)

 

[BabaYaga]

Why obsolete?

Hello,

I have been following this thread with great interest, since I use a split charging system of the same kind as the OP – a simple relay triggered by output from the alternator warning light terminal (D+). This has worked fine since installed five years ago.
To me it seems very likely that the problem lies, as Vic suggests, in the relay beeing triggered by excitation current from the key switch, before the alternator has started to put out. If so, the house battery would have to contribute to engine starting, feeding current through the relay.
In the wiring diagram attatched by the OP there are two fuses 30 A either side of relay – do these exist in the actual set up? It seems they should be blown if the current through the relay was big enough to burn the contacts...
I agree with the suggestion that the relay should be rated at least the same as the alternator. I use a 70 A Bosch relay for a 70 A alternator.
Given this condition I always thought that this method of charge splitting was simple and robust. But...

Frankly controlling the split charging in this way from the warning light circuit is an obsolete method.

...perhaps I am wrong. What are the drawbacks, really? I would be very grateful if Vic or someone else could comment. I hope replies would be useful for the OP also.

 

[richievtu]

an update!
I had another look today, firstly I gave the wrong info about the other (Lucas) relay I mentioned I might try, the relay I have found which must have been the original at some point is in fact a bosch, looks similar to the lucas and although its not stated I assume will be rated at about 70A, also has the correct no's on the terminals, so I wired it up!
It still clicks when the ignition is turned on, checked again there is approx 1.5v at the alt trigger wire & the same on all 3 going to the regulator before the engine is started?
However, this relay seems to work, there is only a drop in voltage at the starter battery when turned over on the key which tells me they must still be isolated at that point?
Once running the starter battery measures approx 13.8v and the leisure battery approx 12.9v after a few minutes ( with the meter reading slowly rising ) does that sound about right or should they be charging at the same voltage? I believe smart relays send proportional current to each battery depending on state of charge.

 

[richievtu]

To answer your question babba, yes my system incorporated the 3 13a fuses and none have blown yet.
I suppose the system is obsolete as the modern intelligent charging methods are more controllable and will charge each battery to its optimum level, probably kinder to gel & agm batteries also, unsure how long my gel battery will last with this method?

 

[earlybird]

an update!

Once running the starter battery measures approx 13.8v and the leisure battery approx 12.9v after a few minutes ( with the meter reading slowly rising ) does that sound about right or should they be charging at the same voltage? I believe smart relays send proportional current to each battery depending on state of charge.

13.8v is on the low side, (14.2 would be better). 12.9v. is much too low for proper charging.
Is your voltmeter accurate though?
Relays are just switches, nothing proportional about them. If the 2 batteries are connected in parallel by the relay, as your circuit shows, then they should be at the same voltage unless you have excessive volt drop in the wires to one battery.

 

[VicS]

I am getting a bit lost.

You found a relay, which you believe may have been the original, you said it was a Lucas SRB146 , but now you say it is a Bosch relay, but you dont say what the part number is.

you say you have fitted it and that it seems to work.

BUT

you say it clicks when the ignition is switched on, suggesting that it is closing, but you say the volts on the leisure battery do not fall when cranking, therefore suggesting that it has not closed. ( it might of course have opened again !)
You say with the engine running you have 13.8 volts on the starter battery but only 12.9 on the leisure battery.
13.8 is a bit too low for effective charging. 12.9 is way too low for any meaningful charging. In any case if the relay is closing and there are no bad connections both should be reading near enough the same.

I have checked the volts at an alternator warning light connection with just the ignition switched on. 1.6 volts! That is with a 1.2watt warning light bulb.
If the volts are higher than that it could be because the warning light bulb is more powerful or it could be due to resistance in the alternator ... bad brushes perhaps.
You said you have a 4 watt bulb. One would then expect to see the volts at the alternator terminal at about 4 volts which is in fact what at one point you said you had.

4 volts may be enough to close the relay but you don't want this to happen. You do not want the relay to close until the engine is running and the alternator is generating!


You need to check the relays you have to make sure they are suitable, both from the closing volts point of view and their current carrying capability. Part numbers are the key, not what they look like!

You need to ensure that the relay does not close with just the ignition switch closed... perhaps by reducing the power of the warning light bulb.

You need to check that when the engine is running the volts on both batteries is near enough the same and that for effective charging it is around 14.2 rather than 13.8.

We still don't know how the glow-plugs are tangled up with all this.

We still don't know why there are apparently two regulators for the alternator.

 

[pvb]

As it seems the electrics on your boat are somewhat suspect, you might be better off getting a marine electrician to check them out.

I stand by this advice!