What size/type of relay for charging system and where to buy it

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Gerry

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Hi folks

I want to reconfigure my alternator charging system with an ignition switch activated relay. I have a 70 Amp Lucas alternator charging 500Ah (4 x 125 Ah) batteries. What size and type of relay do I need and where can I buy it?

Regards

Gerry
 
Gerry said:
I want to reconfigure my alternator charging system with an ignition switch activated relay. I have a 70 Amp Lucas alternator charging 500Ah (4 x 125 Ah) batteries. What size and type of relay do I need and where can I buy it?
Click to expand...

An ignition switch activated relay isn't a great idea, what do you hope to achieve by it?
 
Gerry said:
Hi folks

I want to reconfigure my alternator charging system with an ignition switch activated relay. I have a 70 Amp Lucas alternator charging 500Ah (4 x 125 Ah) batteries. What size and type of relay do I need and where can I buy it?

Regards

Gerry
Click to expand...

If you mean a relay that will disconnect the alternator from the battery when the ignition switch is off and reconnect it when on then you will need a relay with a 12 volt coil ( assuming 12volt system) and contacts rated a little in excess of 70 amps.

You'll easily find a 60 amp Lucas one ....... probably do in fact because it wont be often carrying full current and wont be when you open it but Google will find higher rated relays


Even so not something i would do without good reason!
 
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I was wondering why boats and campers treat separating two batteries differently.

My boat has a 1/2/both switch but charges through a VSR, so almost idiot proof if I remember to treat '1' as House on and '2' or 'both' only for emergencies.

My camper has a split charge relay, so it's impossible to take House power from the starter battery when the ignition is off.

I guess the leisure House battery charges slower in the camper, loses etc. any other reasons for boat set up?

Nick
 
The VSR & "split charge relay" are really the same animal

I use a Victron Cyrix for battery charging & a simple relay that pulls in ( with ignition on) to cut the power to a dump resistor that control my windgen, otherwise the resistor dumps the higher alternator voltage

NickRobinson said:
I was wondering why boats and campers treat separating two batteries differently.

My boat has a 1/2/both switch but charges through a VSR, so almost idiot proof if I remember to treat '1' as House on and '2' or 'both' only for emergencies.

My camper has a split charge relay, so it's impossible to take House power from the starter battery when the ignition is off.

I guess the leisure House battery charges slower in the camper, loses etc. any other reasons for boat set up?

Nick
Click to expand...
 
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NickRobinson said:
They do the same job I agree, but are differently controlled? The SCR is dumb, contacted on engine start, doesn't the VSR monitor start battery health and only connect House when it's happy the Start has had enough?
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Yes, the VSR is an intelligent solution and will only close once the start battery has reached around 13.5v. A split charge relay, particularly one controlled by turning the ignition on, has potential drawbacks.
 
I had the set up you suggest on a Prout cat - worked really well. The engine battery was connected to the engine all the time ( there was an on / off switch on the battery terminal if you wanted to use it) and the charging lead to the domestics went via a lucas relay activated by the engine start switch. From memory the relay was 60 amps which is more than your 70 amp alternator will ever give out in practise.

Much preferable to the usual 1, 2 both switch.
.
 
wotayottie said:
I had the set up you suggest on a Prout cat - worked really well. The engine battery was connected to the engine all the time ( there was an on / off switch on the battery terminal if you wanted to use it) and the charging lead to the domestics went via a lucas relay activated by the engine start switch. From memory the relay was 60 amps which is more than your 70 amp alternator will ever give out in practise.

Much preferable to the usual 1, 2 both switch.
.
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So, let's assume the domestic batteries have been run flat. Go to try to start the engine, as soon as key is turned the engine battery is parallelled to the flat domestics, voltage collapses, engine won't start. What next?
 
pvb said:
So, let's assume the domestic batteries have been run flat. Go to try to start the engine, as soon as key is turned the engine battery is parallelled to the flat domestics, voltage collapses, engine won't start. What next?
Click to expand...

I've got this system. In practice, paralleling a low house battery at start time doesn't appear to affect the starter battery and the engine spins as well as ever. The better solution is to have the relay closed by the charge light current from the alternator (or an oil pressure switch). A bypass switch allows the house battery to be used for starting if required. It's a very simple system that does away with the 1-2-both switch and somewhat cheaper than a VSR.

http://www.troppo.co.uk/odds/Split%20Charging.pdf
 
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alahol2 said:
I've got this system. In practice, paralleling a low house battery at start time doesn't appear to affect the starter battery and the engine spins as well as ever. The better solution is to have the relay closed by the charge light current from the alternator (or an oil pressure switch). A bypass switch allows the house battery to be used for starting if required. It's a very simple system that does away with the 1-2-both switch and somewhat cheaper than a VSR.
Click to expand...

My split charging relay* is activated by the alternator's aux output and an over ride switch is fitted so the domestic battery gets priority (the Sterling regulator senses this battery) I don't have a 1,2 both switch but do have a set of jump leads in case the engine battery should die.

*I use a Tyco 100amp sealed contactor from rsonline.com - not cheap at £100 but a lot more trustworthy than the automotive relays.
 
alahol2 said:
I've got this system. In practice, paralleling a low house battery at start time doesn't appear to affect the starter battery and the engine spins as well as ever. The better solution is to have the relay closed by the charge light current from the alternator (or an oil pressure switch). A bypass switch allows the house battery to be used for starting if required. It's a very simple system that does away with the 1-2-both switch and somewhat cheaper than a VSR.

http://www.troppo.co.uk/odds/Split%20Charging.pdf
Click to expand...

So you charge your batteries through a 40A relay?
 
ianj99 said:
My split charging relay* is activated by the alternator's aux output and an over ride switch is fitted so the domestic battery gets priority (the Sterling regulator senses this battery) I don't have a 1,2 both switch but do have a set of jump leads in case the engine battery should die.

*I use a Tyco 100amp sealed contactor from rsonline.com - not cheap at £100 but a lot more trustworthy than the automotive relays.
Click to expand...

the Tyco is also more expensive than my Victron Cyrix
 
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