DC/DC converter output limit

Has anyone found a spec for the output capacity of the converter?

All along I've been thinking 100 amps, because of that DC/DC fuse in the distribution block near the inverter - but looking again at the "power source" pages in the wiring diagram I notice for the first time that the 100 A fuse isn't the first thing from the converter: heat (fan and PTC), cooling fans, EMPS, ABS 1 and 4, plus the ACC, IG1, and TAIL circuits and a bunch of stuff including the rear defog, are taken off the converter side of the 100A fuse, and then there are more fairly substantial loads including headlights, ABS 2 and 3, IG2, etc., on the battery side of the fuse. (I'm looking in the Classic diagram; I don't know if that's similar for the NHW20.)

Does anyone have a measurement or an explicit spec for the maximum design output current for the converter? Has anyone found the output current at which the converter asserts the IDH signal asking the climate control to avoid PTC heat? (Hmm ... I wonder if IDH comes on at a fixed current, or depends on something like converter temperature).

Thanks,
-Chap

 

That's a great write-up, thanks!

Might you still happen to have the cardboard pattern for your hinged cover panel? It would be cool if you could draw a known ruler-length on it somewhere, then post a photo taken from perpendicularly above.

It looks like you didn't try the Hall effect clamp right at the converter outlet to see what its total output was while you were drawing 75A in addition to the normal loads. But I guess it can be inferred from your load/no-load comparison that the normal loads were about 23 amps, and so it was producing ~ 98 A total under your 1 kW load test. (Ok, actually that's an overestimate, because the base fuel burn doesn't just reflect electrical output, but all losses in running the engine.)

I'm still curious at what level of load the IDH signal comes on. Am I the first to wonder?

-Chap

 

I am - that looks like a very tidy installation you've got there.

... a signal carried on a yellow wire from C4 pin 2 at the converter to A7 pin 10 at the A/C controller. The HVAC system includes a few hundred watts of electric resistance heat (a couple elements integral to the heater core and, for certain sales regions, a couple more in the footwell air duct) as a supplement in cold conditions before the engine coolant is up to temp. These PTC heating elements are only turned on:

• for certain settings of the A/C controls
• when coolant temp is below a threshold, and
• when electrical capacity allows

The IDH signal seems to be how the A/C controller knows about that last condition. I have not confirmed this exactly and I'm inferring a little beyond what I can actually find in the books, but my guess is that the converter asserts IDH to ask the A/C to disable electric heat, when the load on the converter is within some margin of maximum.

The diagnostic book actually makes it sound like the PTC heat depends on a set of specific load conditions (headlights off, rear defog off) but I suspect that's just the diag book giving you a guaranteed condition where you should be able to see the PTC heaters operate. It makes more sense to me that the real condition for suppressing the PTC heat would be a simple 'too much load' signal from the converter rather than a bunch of specific load conditions.

-Chap