Is my split charge relay adequate?

[Born Too Late]

Hi

the wiring connecting my batteries to the split charge relay was pretty shoddy (no fuse on the leisure battery, 20 amp fuse holder with 25 amp fuse on the main battery, badly crimped etc.) and after reading through the wiki I decided to replace it all.

My relay is a Lucas 33441 33RA like this one

http://www.autoelectricsupplies.co.uk/p ... tegory/113" onclick="window.open(this.href);return false;

The wiring diagram says to use 65/0.30 cable but I've used bigger 84/.030 and added 30 amp fuses close to each battery. When I bought the van it needed a new leisure battery so I replaced it with the biggest I could fit in (115 amp), my worry is that the relay might now not be up to the job (I think it's rated at 60 amps), do I need to replace it with a bigger one?

Many thanks

Wes

[AdrianC]

the wiring connecting my batteries to the split charge relay was pretty shoddy (no fuse on the leisure battery, 20 amp fuse holder with 25 amp fuse on the main battery, badly crimped etc.) and after reading through the wiki I decided to replace it all.

My relay is a Lucas 33441 33RA like this one

http://www.autoelectricsupplies.co.uk/p ... tegory/113" onclick="window.open(this.href);return false;

The wiring diagram says to use 65/0.30 cable but I've used bigger 84/.030 and added 30 amp fuses close to each battery. When I bought the van it needed a new leisure battery so I replaced it with the biggest I could fit in (115 amp), my worry is that the relay might now not be up to the job (I think it's rated at 60 amps), do I need to replace it with a bigger one?

Don't get confused between the current flow - the amps that the alternator can put out and the relay can handle - and the capacity of the battery - the amp-hours.

Think of the amp-hours as the size of a water tank, and the current as the flow rate of the water going into and out of it.

Your potential maximum current going into the leisure battery is the alternator's output - which could be up to 90A, depending on which alternator's on your van. It's unlikely that you'll see that much, but it's possible.

If you've got 30A fuses, then they'll blow before you have a problem with the relay or the wiring.

[Born Too Late]

Thanks for the reply AdrianC, I thought I must be getting confused somewhere along the line. I think it's a case of the more I learn, the more I realise I don't know!

This is some of the wiring I removed from the 2 batteries:



and this lovely little bit was hiding in the tow bar wiring:



So far I've removed all trace of the tow bar electrics to be done properly at some future point.

Thanks again

Wes

[California Dreamin]

the wiring connecting my batteries to the split charge relay was pretty shoddy (no fuse on the leisure battery, 20 amp fuse holder with 25 amp fuse on the main battery, badly crimped etc.) and after reading through the wiki I decided to replace it all.

My relay is a Lucas 33441 33RA like this one

http://www.autoelectricsupplies.co.uk/p ... tegory/113" onclick="window.open(this.href);return false;

The wiring diagram says to use 65/0.30 cable but I've used bigger 84/.030 and added 30 amp fuses close to each battery. When I bought the van it needed a new leisure battery so I replaced it with the biggest I could fit in (115 amp), my worry is that the relay might now not be up to the job (I think it's rated at 60 amps), do I need to replace it with a bigger one?

Don't get confused between the current flow - the amps that the alternator can put out and the relay can handle - and the capacity of the battery - the amp-hours.

Think of the amp-hours as the size of a water tank, and the current as the flow rate of the water going into and out of it.

Your potential maximum current going into the leisure battery is the alternator's output - which could be up to 90A, depending on which alternator's on your van. It's unlikely that you'll see that much, but it's possible.

If you've got 30A fuses, then they'll blow before you have a problem with the relay or the wiring.

The theory isn't quite that straight forward as in reality once the relay connects both batteries together the alternator see's just ONE big battery. Even with a heavily discharged leisure the alternator reads an average of the two batteries and charges accordingly. In reality (and I've tested this for myself) there is an initial high amp surge (when you first start the engine) in the high 30's, which quickly (after 5 - 10 seconds) drops in the mid 20's.
This is roughly of course but you get nowhere close to 90 amps of the alternator.
Of course you never really want to flatten the leisure beyond 12 volts, and in those circumstances the initial draw in even less.
That 60 amp dedicated Lucas relay is ideal, bare in mind many basic split charge systems run very inadequate 30 amp relays.
Keep with the 30amp fuses and change them on the 'odd time' they blow. Make sure all other battery connecting wiring is rated 45amp plus.

Martin

[Born Too Late]

Thanks Martin, I'd seen some really heavy duty relays being advertised and used elsewhere and was starting to think mine was a bit weedy in comparison. I'm definitely reassured that it won't catch fire under my seat

Next immediate job is to take everything out again to charge the main battery. I was testing everything still worked after replacing the cable/removing the tow bar wiring and like a numpty left the headlights on. Haven't checked it's actual charge yet but it was only 11.99 volts on Sunday and barely started the engine.

Wes

[California Dreamin]

You don't necessarily have to remove the battery to charge it, as long as you can get power to the van to connect a charger.
In regard of split charge setups generally: Some of those bigger relays can actually be a problem as they can no longer be switched using the small blue alternator exciter wire (too much current to operate the relay switching). I've even seen owners use one relay to switch a heavier one quite frankly, on a two battery setup this is just unnecessary... but decisions about charging seem to get totally out of proportion to need.
What also makes me chuckle, is the reasoning behind fitting very heavy relays (140 amp) and then connecting them up with 35 - 50 amp wire and then fitting 30 amp fuses.
If a 30 amp fuse is blowing once a year, whats that telling you about how much current in flowing?

Martin

[kevtherev]

..... but decisions about charging get totally out of proportion to need.

Amen brother.