Split charge relay on 311 CDI - Mercedes-Benz Forum
 
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post #1 of 8 (permalink) Old 08-20-2011, 03:15 AM Thread Starter
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Split charge relay on 311 CDI

Have done a lot of searching on the Sprinter forums but not been able to find a clear answer. Hope someone can help out.

Where is the best place to wire in a split charge relay on a 2003 311 CDI?

The likely place seems to be in fuse/relay box the under the drivers seat where there appears to be some available(?) heavy-duty wiring directly from the van's battery taped-up in the seat box. These are currently all bound together and insulated. Are they in there for this kind of purpose? If so, I could tap into them to provide the 12v feed to the relay. Or is it better to run a dedicated heavy-duty cable directly from the van's battery to the relay? (Seems redundant if a suitable feed is already there.)

Next, where do I pick up a connection from the alternator signal lead to switch the relay. According to the Haynes manual it's a blue wire. I've checked the dashboard connections and sure enough there's a blue wire there. But nowhere to suitably tap into it that I can find. Anyone point me in the right direction?

Alternatively, I've considered just tapping into a signal lead that's only live when the ignition is on. As a reasonable compromise. Of which there is an 'available' cluster of blue/black wires in the driver's seat box which meet the requirement. Any issues with taking this approach if I can find the alternator signal lead?

Incidentally, I have a 70amp relay with 40amp fuses to protect the wiring on either side of the relay.

Appreciate any help with this.
Thanks, Ian
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post #2 of 8 (permalink) Old 08-20-2011, 05:39 AM
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Originally Posted by ithody View Post
Have done a lot of searching on the Sprinter forums but not been able to find a clear answer. Hope someone can help out.

Where is the best place to wire in a split charge relay on a 2003 311 CDI?

The likely place seems to be in fuse/relay box the under the drivers seat where there appears to be some available(?) heavy-duty wiring directly from the van's battery taped-up in the seat box. These are currently all bound together and insulated. Are they in there for this kind of purpose? If so, I could tap into them to provide the 12v feed to the relay. Or is it better to run a dedicated heavy-duty cable directly from the van's battery to the relay? (Seems redundant if a suitable feed is already there.)

Next, where do I pick up a connection from the alternator signal lead to switch the relay. According to the Haynes manual it's a blue wire. I've checked the dashboard connections and sure enough there's a blue wire there. But nowhere to suitably tap into it that I can find. Anyone point me in the right direction?

Alternatively, I've considered just tapping into a signal lead that's only live when the ignition is on. As a reasonable compromise. Of which there is an 'available' cluster of blue/black wires in the driver's seat box which meet the requirement. Any issues with taking this approach if I can find the alternator signal lead?

Incidentally, I have a 70amp relay with 40amp fuses to protect the wiring on either side of the relay.

Appreciate any help with this.
Thanks, Ian
Hi Ian

First why do you want to have a second battery ?
I am not sure if you can use the wiring under the seat, but what I would do is use one of these:
Self-Switching Combination Relay Towing Relays Wiring Components and Accessories Towing Electrics Towin...
and wire it to trigger your high amperage relay, the reason I suggest this, its easer to wire this any where rather than do all the wiring at the alternator, and run a heavy cable direct to the 2nd battery.

Hope that makes sense

Radiotwo
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post #3 of 8 (permalink) Old 08-20-2011, 11:30 AM Thread Starter
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Thanks for the info RadioTwo.

The second battery will be a leisure battery for the camper conversion I'm doing to the Sprinter. Yes, I came across the self-switching combination relay option when researching the forums earlier. Decided against it due to it only being rated at 30amps and the alternator could generate more. But had not considered using it just to switch my 70amp relay. Seems a bit of overkill though since I already have a suitable relay. I just need a suitable (accessible) signal wire. But from where ....?

Cheers, Ian
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post #4 of 8 (permalink) Old 08-20-2011, 12:42 PM
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Thanks for the info RadioTwo.

The second battery will be a leisure battery for the camper conversion I'm doing to the Sprinter. Yes, I came across the self-switching combination relay option when researching the forums earlier. Decided against it due to it only being rated at 30amps and the alternator could generate more. But had not considered using it just to switch my 70amp relay. Seems a bit of overkill though since I already have a suitable relay. I just need a suitable (accessible) signal wire. But from where ....?

Cheers, Ian
Hi Again

You will be surprised, 30amp will be sufficient most caravanner's use those self switching units for both battery charging and running the fridge's (as I do)

Most batteries will take less than 30 amps, unless you are drawing a lot off it at the time of charging!

Where are you thinking of putting the battery ?

Just to go back to the wiring of the relay, I know how it is wired but harder to explain !

these are the pin outs on the relay:

pin 85 goes to the sense wire on the alternator ( the wire that goes to the warning light on the dash, some times labled as WL)

pin 86 goes to earth.

pin 30 goes directly to the van battery

pin 87 goes to the leisure battery

The way it works is: when you turn on the IGN (turn the key) and the battery light comes on, there is a 12 volt feed from the switch, and it goes through the bulb to the alternator and earth's,but when you start the engine and the alternator starts to charge it puts more than 12 volts on the other side of the lamp so it goes out, but that means the terminal 85 becomes live when it is charging, so switches the relay and in turn charges the leisure battery.

Hope that helps

If you need any more help, please PM me

Radiotwo
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post #5 of 8 (permalink) Old 08-21-2011, 03:33 AM Thread Starter
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The leisure battery will either go in the driver's seat box (if it will fit with relays/fusebox already in there) or more likely in the passenger seat box. The relay and wiring will be in the driver's seat box.

I'm familiar with wiring in relays as I've done so for the electric windows. But thanks for confirming the wiring. The main thrust of the post was to try to find out what the existing (unused) wiring under the driver's seat is actually for. I suspect it's there to offer easy expansion of the electrical system for adding new components ... like a split charge system? But didn't want to disturb the existing wiring loom without first asking the question. Just hopeful someone out there knows and can confirm.

Thanks again for the input.
Cheers, Ian
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post #6 of 8 (permalink) Old 08-23-2011, 12:33 AM
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Hi Ian

I think you know who I am !

Anyway

That stub of wires under driver seat is the tail end where all cables join, you can tee off of there, you will find a swithched an perm supply there capable of running what you need,

Best to go with a proper relay, some self switching relays paly up , so choose wisely, hate to see you stranded with a flat battery.

What type of passenger seat do you have?

As I have a battery tray that bolts under a double seat, you can then run the cable under the seats in the wiring channel.

Make sure everything is fused, We can supply a second fuse holder to go in next to the existing holder under the driver seat with connectors, So is neat and tidy

Bruce
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post #7 of 8 (permalink) Old 08-23-2011, 12:57 AM
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Hi Ian

I think you know who I am !

Anyway

That stub of wires under driver seat is the tail end where all cables join, you can tee off of there, you will find a swithched an perm supply there capable of running what you need,

Best to go with a proper relay, some self switching relays paly up , so choose wisely, hate to see you stranded with a flat battery.

What type of passenger seat do you have?

As I have a battery tray that bolts under a double seat, you can then run the cable under the seats in the wiring channel.

Make sure everything is fused, We can supply a second fuse holder to go in next to the existing holder under the driver seat with connectors, So is neat and tidy

Bruce
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post #8 of 8 (permalink) Old 08-23-2011, 01:33 AM Thread Starter
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Hi Bruce,

Fantastic job on fixing my "Start error" issue so quickly BTW. Thanks again for that.
If anyone else has a similar problem Bruce is your man. Turned around my fix in 24 hours flat. Great service.

Regarding my split-charge setup ... thanks for confirming what I thought was the case. On reflection, rather than cutting into the main positive feed under the driver's seat and having to re-crimp it all again, I'm considering taking a dedicated battery cable direct from the main battery terminal to the passenger seat box where I'll house the leisure battery, switch relay, and camper fuse box. Then tap into the 'ignition on' feed from under the driver's seat. Should make things pretty simple. Going to use a 70amp relay with in-line 40amp fuses on either side that I've already sourced for the job, along with a 8-way fusebox for the camper interior stuff.

Interested in the bolt-in battery tray you have for under the passenger seat. Can you PM me on the details.

Thanks as always for your invaluable knowledge and experience. What would this forum be without you!

Cheers, Ian
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