Replacing Schaudt B2B - D+ Puzzle

[fred_jb]

I wonder if anyone can help me to understand the D+ arrangement on my Schaudt B2B. The D+ input is sourced from the EBL 31 generated by a relay fed from the B pillar connector with the engine on and ignition on signals. However the current B2B is not fed directly from the D+ busbar which distributes the D+ output from the EBL 31. Instead this is switched via a relay with relay coil being powered from one of the 12V outputs on the EBL - see diagram below. This seems to imply that the B2B will only be enabled if the 12V system master switch is on, and I don't understand why that should be. The vehicle is an Etrusco Ducato based PVC, with Etrusco being an Italian branch of the German Hymer group.

The reason I want to understand this is because I am doing a major upgrade to the 12V system and am fitting a lithium battery ( see pic below) and other bits including a Renogy combined B2B and MPPT solar controller. The output from the new B2B will go directly to the new battery and not via the EBL so I don't see any reason why its D+ input cannot be supplied directly from the D+ source and not be switched by a relay.

 

[autorouter]

Most B2Bs are indeed wired so that they are triggered by the D+ signal, so they are on all the time the engine is running, and definitely off when the engine is not running. However some people like to be able to switch the B2B on and off for various reasons. In which case putting a switch or relay in the D+ path will allow that possibility.

For example, if you have several hundred watts of solar and a B2B, you might find that with only one or two lead-acid batteries they might be overcharged in full sun. So switching off the B2B would probably be a good idea. I think if you upgrade to lithium you would have to work quite hard to produce a charging amps level that is too much for a lithium battery. So I imagine there's no need for this relay arrangement, just run it directly on the D+ signal.

This D+ signal, from Block1 Pin2, is wired directly inside the EBL to Block2 Pin3, which is the D+ coming into the EBL. So it's a good signal if you need it. It is used to switch the fridge over from gas to 12V when the engine is running.

 

[fred_jb]

Most B2Bs are indeed wired so that they are triggered by the D+ signal, so they are on all the time the engine is running, and definitely off when the engine is not running. However some people like to be able to switch the B2B on and off for various reasons. In which case putting a switch or relay in the D+ path will allow that possibility.

For example, if you have several hundred watts of solar and a B2B, you might find that with only one or two lead-acid batteries they might be overcharged in full sun. So switching off the B2B would probably be a good idea. I think if you upgrade to lithium you would have to work quite hard to produce a charging amps level that is too much for a lithium battery. So I imagine there's no need for this relay arrangement, just run it directly on the D+ signal.

This D+ signal, from Block1 Pin2, is wired directly inside the EBL to Block2 Pin3, which is the D+ coming into the EBL. So it's a good signal if you need it. It is used to switch the fridge over from gas to 12V when the engine is running.

Thanks for your thoughts on this. Interesting suggestion that you might want to switch the B2B off as this had not occurred to me. In this case though there is no dedicated switch to turn this relay off as it is simply permanently connected to one of the 12V outputs on the Electroblock.

This means that as long as the Electroblock is switched on with the master 12V on/off switch on the wall mounted control panel, then the B2B will operate. I was totally unaware of this and it means that if we had the 12V system switched off while travelling then we would get no alternator charging of the leisure battery. I'm pretty sure this is not mentioned anywhere in the manual!

My new B2B automatically charges preferentially from the alternator while the engine is running and only switches its input to solar when the engine is off. I think you can change this setting but I haven't explored that yet.

 

[autorouter]

My new B2B automatically charges preferentially from the alternator while the engine is running and only switches its input to solar when the engine is off. I think you can change this setting but I haven't explored that yet.

I'm not very familiar with the Renogy B2B/Solar, but I've heard that the B2B side only gives the full output with no solar. With the slightest amount of solar it reduces the B2B output to half, to allow for the solar. Some people put a switch in the solar side to switch off the solar completely so that the B2B gives full output.

 

[fred_jb]

Actually I only skimmed the manual so what I said earlier isn't quite right. On reading it again it seems a bit more complicated with switchover to alternator only depending on solar dropping below a preset current level which is user adjustable, but if you wanted to force this you could switch off the solar panel input. The device will also charge the starter battery if certain criteria are met, such as adequate solar power and leisure battery having a high enough state of charge.

 

[paddymcc]

I think it's worth having the option of turning off the b2b. It means you can stop the battery being fully charged when returning from a trip. As lithium don't like being stored fully charged it makes sense to have this option.
I put a LED illuminated switch in the D+ that is on the seat base and I can access it whilst driving.

 

[fred_jb]

I'm not very familiar with the Renogy B2B/Solar, but I've heard that the B2B side only gives the full output with no solar. With the slightest amount of solar it reduces the B2B output to half, to allow for the solar. Some people put a switch in the solar side to switch off the solar completely so that the B2B gives full output.

You can set the B2B to use only the alternator input if the solar drops below a set level, though I think the highest you can set that is 10A. My solar maxes out at about 18A on a good day so with this setting if the solar is above 10A you get solar plus 25A, so between 35A and 43A in my case. If solar is below 10A you get 50A from the alternator with the solar being ignored.

I already have a 2 pole switch in the solar feed so I guess I could use this to force alternator only charging if I wanted, even when it is outputting over 10A, but overall I am happy to keep solar connected and reduce the alternator load which will in turn slightly reduce fuel consumption.

 

[fred_jb]

I think it's worth having the option of turning off the b2b. It means you can stop the battery being fully charged when returning from a trip. As lithium don't like being stored fully charged it makes sense to have this option.
I put a LED illuminated switch in the D+ that is on the seat base and I can access it whilst driving.

Good idea, it would be easy for me to repurpose the relay which was connecting the D+ signal to the old B2B, but operating it with an easily accessible dedicated switch.

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