Dometic Coolmatic CD30 fridge wiring question

[WhiteBear]

If you need a 12V output that is not switched via the overhead panel and always has power, you can use the one under the rear right seat. It just needs to be fitted with a plug. I have an Anderson plug on it for the portable compressor, for example. But it runs off the main battery.

There were no terminal covers on my auxiliary battery, let alone seals. However, you @Logsplitter are probably right that Ineos does not want any consumers connected directly to this battery.

But I don't care, I don't want the switch on the overhead panel to always have to be turned on when the refrigerator is running and connected to the socket in the boot. And I don't want the power to come from the starter battery either.

I have equipped both batteries with a monitor, so I can check the voltage via an app. In addition, I have a live voltage display with remote monitoring via the Webasto auxiliary heating system and its app. That should be enough; if the auxiliary battery runs out, it's not a big deal to me.

I don't really understand the point of the Ineos solution with Smartpass anyway. I would have found a real starter/consumer battery configuration more sensible for a car like this. That's why I'm going to connect the refrigerator directly to the auxiliary battery soon, including a 30A safety switch.

 

[Logsplitter]

If you need a 12V output that is not switched via the overhead panel and always has power, you can use the one under the rear right seat. It just needs to be fitted with a plug. I have an Anderson plug on it for the portable compressor, for example. But it runs off the main battery.

There were no terminal covers on my auxiliary battery, let alone seals. However, you @Logsplitter are probably right that Ineos does not want any consumers connected directly to this battery.

But I don't care, I don't want the switch on the overhead panel to always have to be turned on when the refrigerator is running and connected to the socket in the boot. And I don't want the power to come from the starter battery either.

I have equipped both batteries with a monitor, so I can check the voltage via an app. In addition, I have a live voltage display with remote monitoring via the Webasto auxiliary heating system and its app. That should be enough; if the auxiliary battery runs out, it's not a big deal to me.

I don't really understand the point of the Ineos solution with Smartpass anyway. I would have found a real starter/consumer battery configuration more sensible for a car like this. That's why I'm going to connect the refrigerator directly to the auxiliary battery soon, including a 30A safety switch.

I understand where you’re coming from. When I ordered the dual battery setup I had in mind a traditional setup. As in starter and house battery with either a voltage sensitive relay or DC to DC charger. For now I’ll live with Ineos setup but when either of the batteries failes I’ll probably change to a more traditional house/consumer battery linked with a DC to DC charger to the starter battery.

 

[Glen]

I suspect this discussion is going beyond what the OP had in mind

If INEOS has blocked off the service battery load port on the Smartpass, then I’d guess the second battery + Smartpass was intended to address a very specific problem. BMW’s implementation of their Intelligent Battery System (IBS) has been criticized in the past for maintaining the starter battery at less than 100%.

As I understand it, IBS is trying to maintain an SOC around 70% so the battery can always accept charging upon deceleration or no load on the engine. Imagine a scenario where you’re climbing a mountain pass for two days with lots of stop/starts (not the automated kind, but where you turn the engine off, scout the route, then come back and start the engine again). Then throw in 3 or 4 sessions of using the winch to extricate the vehicle. I can imagine that the charge system could fall behind and you’d end up in a position where the battery would become so depleted it could no longer start the engine . . . before you got to the top of the mountain.

Eventually, you’d descend that mountain, and IBS would be charging your battery for nearly the entire descent. I suspect the second battery was intended to add extra capacity so you could always get over the top of mountain under “typical” or “expected” conditions (as defined by INEOS) without draining the single battery to a no-start condition. According to the CTEK documentation, the Smartpass dumps service battery current into the start battery for the first ten seconds of an engine start - that’s how the vehicle accesses the extra capacity of a second battery to protect against a too-depleted start battery.

One of the best laziest ways to figure something out is to post it on the internet and wait for the inevitable corrections to roll in. So I’m going to keep speculating. I’d further guess the 2-battery solution was a speculative fix that was either eventually determined to be unnecessary, uneconomical for INEOS, or it was obviated by a slight modification to the IBS software.

So @Barrett1 , if all my speculation is true, then INEOS never intended any loads to be connected to the service battery (or else they wouldn't have blocked off the low-priority service battery load port on the Smartpass).
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I don’t really see any downside to contradicting INEOS’s intentions of only connecting loads to the start battery, and this seems to be borne out by the experience reported by @AaronS . Or you could connect your load to the starter battery via the cigarette lighter, the fuse panel or via direct connection. Both batteries are connected during engine-on ops, and both batteries eventually get charged.

Some final thoughts . . .

- If I had the dual battery system and wanted to use the second battery as a house battery, I’d get rid of the Smartpass and install a DC-DC charger with a power distribution relay to disconnect the charger when the engine was off. But I don’t and won’t since I tow a small overland type trailer with its own house battery and DC-DC charger / solar controller.

- I live on top of a mountain, so anytime I go somewhere, I immediately descend 2,000 feet with engine braking the whole way. I was watching the SOC on a descent the other day. At the bottom of my descent, SOC was 96% (observed similar on several runs). This is what makes me think INEOS may have tweaked the IBS function, since that is far above the 70% SOC target all the IBS docs seem to reference.

 

[Tom109]

I have an occasional use Engel MT45, so it’s in/out of the Gren all the time. I really like the convenience of the 12v DC plug, and the convenience of the overhead switch to power the fridge with engine off. I may eventually wire a direct feed from the starter battery, but with the Engel’s low draw it’s not really necessary.

 

[Tom109]

As I understand it, IBS is trying to maintain an SOC around 70% so the battery can always accept charging upon deceleration or no load on the engine. Imagine a scenario where you’re climbing a mountain pass for two days with lots of stop/starts (not the automated kind, but where you turn the engine off, scout the route, then come back and start the engine again). Then throw in 3 or 4 sessions of using the winch to extricate the vehicle. I can imagine that the charge system could fall behind and you’d end up in a position where the battery would become so depleted it could no longer start the engine . . . before you got to the top of the mountain.

The IBS:SoC is a joke. I put 200W of solar on my roof to support my Engel MT45. If I park in the garage I’m still at the mercy of the IBS, but out in the sun and I’m in the 90+% SoC all the time.

 

[AaronS]

Good summary @Glen.

I will add that we received our truck Dec 2023, it was an early one in the US. At the time I could not find reliable info as to how the OEM dual battery system functioned. So I went with what I knew and wired the Engel to (what I now know is) the starter battery. It wasn't an informed decision though. As time passes and it continues to work without issue... I haven't bothered to put more thought into it.

How do you use your truck? Daily? Only a few times a year so it sits a lot? When you are using it for camping do you base camp so the truck sits un-started for days at a time?

IMO, if your trucks sits a lot (whether it be in a garage or at a base camp) and you want/need to be able to run the battery down and then still start the truck, you may want to use the service battery and keep the starter battery in reserve. Or add solar as @Tom109 mentioned.

My truck rarely sits for more than 2-3 days at a time so I am rarely running either battery down that much. And I carry a jump box just in case.

 

[WhiteBear]

I also installed the Ctek 250 for solar charging. This is currently not used in practice because the car is parked in the garage or under a large tree. In both cases, shore power is available, so battery maintenance is always carried out in the garage using a Victron charger that is permanently installed in the car. The car sometimes stays there for 3-4 weeks.

I also use the Victron regularly at the parking spot under the tree because the batteries do not charge properly with the auxiliary heating and the short distances (20-30 km). This is especially true when temperatures are around -10 degrees and below. Solar is not an option there.

As a backup, I also have a Noco jump starter in the car.
My scenario for connecting the refrigerator to the auxiliary battery is for medium-length journeys, where I often stop for a while and don't want all the other devices connected to the main battery to continue running because the overhead switch has to be on for the refrigerator.

This may be different for others, but perhaps the power connection under the rear seat bench, which is connected to the main battery, would be a good option.