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Randall, RVIA Certification
Category: RV
Satisfied Customers: 11054
Experience:  RVDA/RVIA Master Certified Technician with many years experience.
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I have a Dometic type C40 /110 AES - when connecting the S+

Customer Question

I have a Dometic type C40 /110 AES - when connecting the S+ for solar sensing to a Solar MPPT Regulator, in this case a Redarc BMS1230S2, what terminal /wire should I put it to??
Also where/what should I connect the D+ wire to.
Regards David
Submitted: 1 year ago.
Category: RV
Expert:  Randall replied 1 year ago.

I am attaching the manual which covers this mode for you. Please see Section 6.9.3 for instructions on these hookups. D+ connects to the signal wire off the alternator in your vehicle. Hope that proves helpful here. Please get back to me if you need more as all follow ups are included in our fee.

Expert:  Randall replied 1 year ago.

You didn't ask, but the other negative lead off the controller has to be hooked up as well. That would be on "C" according to that section.

Expert:  Randall replied 1 year ago.

I am adding a link to the Redarc BMS1230S2 for you in case you don't have one already. Read it carefully so you understand all the functions it has and controls here. Again............get back to me if you need more as all follow ups are included and fully expected.

Expert:  Randall replied 1 year ago.

See page 20 in the manual showing the ignition trigger. So it has to receive one as well here. Use a connector wire to hook up from D+ to that spot on the controller.

Customer: replied 1 year ago.
I have both of these manuals, the fridge is a RMD8555 have that manual also. I have since spoken with technical at Redarc - they say they have no terminal on there BMS that will indicate / signal the fridge S+ as required -need to know what the signal is. Spoke with Dometic Australia and they have indicated 'that they have never used the S+ or the D+ and recommended that i don't use them either - a pretty un-helpfull answer and they didn't offer any other help at all!! So now to proceed ----- i need to know what the S+ signal is, a particular voltage - a particular amperage or what !! What are your thoughts???
The D+ I can do without.
Expert:  Randall replied 1 year ago.

That "signal" is nothing more than the actual voltage from the alternator when the vehicle is running. It is probably about 14.5 VDC or in that range. It just alerts the Redarc module that the engine is running. Sounds like the person you spoke to at Redarc really doesn't understand the product. If it isn't needed, then why have it????? When we hook up solar on an RV we just hook up the positive feed and negative feed right into the batteries OR the system at the back of the fridge if that is easier to get to. The fridge doesn't care where the power is coming from! It is either from the AC feed or the batteries or in the case of a 3 way fridge, the ignition side and ONLY will run on 12 VDC mode IF that feed is energized. I suspect that this is the same. You don't want the fridge to try and run on 12 VDC UNLESS the engine is running. Otherwise, it will suck the batteries right down in a jiffy as the solar panels won't be able to keep up (unless there are a bunch of them) and most RVs don't have room for that many! I live off-grid, so I do know a few thing about solar. Hope that clarifies this some. Get back to me if you need more on this.

Customer: replied 1 year ago.
Manual for RMD8555 P10 says Fridge's rated at 170w @ 12v and i have 450 watt of panels on the roof of the van (25 footer)
The problem with connecting directly to the batteries is that the fridge will run on the solar whilst the sun shines but has no way of knowing when the 'sun don't shine' and will run on battery until manually switched over instead of automatically going to gas via the AES. We go to outback Australia for long periods with no AC power for up to 4-500km (toooo long a lead!!)
Redarc is capable of going to 520w if needed but i recon i have a fair leeway. Seems i may have to make something up to do the job.
Expert:  Randall replied 1 year ago.

You do have to use a controller of some sort........and keep in mind you are using more power than just the fridge. If you don't want the fridge to switch over to LP at night you need to have more power stored up in your batteries and the more the better. Figure our your amp draw and see how many amp hours worth of deep cycle batteries you have. Keep in mind that you don't want to draw them down to under 11 VDC. The fridge won't run and it is hard on the batteries. Add the amps that the controls on the fridge use as well.

Expert:  Randall replied 1 year ago.

When I get to work later today I will look up the information on one we use and get it to you..........

Customer: replied 1 year ago.
I am using the Redarc controller and this whole conversation is about having the fridges AES switch itself to LPG at night or when insufficient solar is available, I have no intension of running the fridge on batteries alone. I will run it on 12v for a while and log the amps it uses. The low voltage protection on the Redarc will protect the batteries. I think i am going to have to contact Dometic in Germany to have them explain the signal requirements of the S+ function.
Expert:  Randall replied 1 year ago.

The Owner's manual gives you that.....and I explained it to you. Not much more on this subject I can add here.

Expert:  Randall replied 1 year ago.

Just checking back to see if you got all you needed on this from me and if you were able to get this all hooked up o.k.?