Electro-philes: crit a 280Z HL diag.

[ensys]

 

So, here's a new 280Z headlight relay wiring diag. that needs some vetting by experienced minds.

As will become apparent, this is no quickie solution, as it entails reversible modifications at a couple connectors and a few hard-to-source parts.

On the plus side, it addresses issues like low-amp switching at the rotary combination, using the (E) power source for relay actuation, and allows keeping the relays inside the cabin. Plus, it includes the Hi-Beam indicator on the Speedo and it frees two spots at the fuse panel (fog lights?).

Note: the fuses are sized for stock incandescents, but the wire sizes will accommodate hotter bulbs.

So look it over and, if you will, offer corrections/adjustments as needed.

If elements look familiar, it's because the diag. was built on the bones of a previous effort for 240s (with a special thanks to it's Author).

Your attention, help, and support are appreciated.

 

[ETI4K]

Just saw this, so my comments may be moot. Interesting design. Nice graphics.  What year is your car?

It looks like your shunt diodes are across the coil, while they should be across the contacts.  The arc you are trying to suppress will occur at the contacts.  The 20A fuses are probably too high.  OEM are 10A, IIRC.  If you're planning to use LEDs, then the current will be even less.  What are you trying to protect: relays, wiring, bulbs?  While a 20A relay will run to 20A, it shouldn't ever.  Ideally, you'd like max load <80% of rating so you can have some margin of protection - call it safety factor.  A 55W halogen would run just over 4A at low battery charging voltage (13.5V), so a 10A fuse should be adequate.

As for wire gauges, as a general guideline, 350CMA (circular mil area) per amp will provide good service with acceptable IR loss.  A 12AWG wire will certainly easily handle 4A, and if you are into the wire harness anyway, maybe it's no big deal.  It's just not necessary for your intended purpose.  That is as long as you're not wiring against what we used to call the gorilla factor - you're trying to prevent some monkey who might be working on your car from damaging a small wire through lack of care.  In such cases, then 12AWG might be just right.  As an example, the 12AWG wire is about 6500CM which should be good for more than 18A.

Also, it looks like you trying to energize the coil of your HB relay through the indicator lamp?  Not sure if that's actually the plan, but you may find the relay is jumpy without a good, solid connection to ground.  Some relays don't need quite as much coil current to throw as others might. I'd suggest grounding one side of the coil, and using your stalk switch HB signal on the other.  Tie the HB indicator to pin 87 on your HB relay.

Have fun.

[Captain Obvious]

16 hours ago, ETI4K said:

It looks like your shunt diodes are across the coil, while they should be across the contacts.  The arc you are trying to suppress will occur at the contacts. 

The 20A fuses are probably too high.  OEM are 10A, IIRC. 

 

Also, it looks like you trying to energize the coil of your HB relay through the indicator lamp? 

As you said, all of this is probably moot, but thought I have some comments.

First, the shunt diodes are in the correct place. You're trying to squelch the flyback kick from the relay coil. The relay contacts are on the secondary side and have absolutely nothing to do with that. Many relay manufacturers include diodes inside the relays already (in the correct circuit location), and that's what it looks like the OP was planning to use.

Second, the original 10A fuses each powered just one headlight side. But in this new scheme, each 20 fuse powers BOTH sides at the same time. Not getting into whether it's completely appropriate or not, doing the math simply doubles up the original fuse size from 10A to 20A. You did the math and came up with 4A for each bulb... I wouldn't want to run 8A continuous (from both sides at the same time) through a 10A fuse.

Lastly. the connection to the high beam indicator is fine. The HB indicator bulb is in parallel with the relay, not series. They both get "drug to ground" through the switch.

OK... I'm back into my hole now.  Haha!!

 

[w3wilkes]

Not being familiar with the original 280Z wiring, but on a 240Z with the NLA Dave Irwin headlight wiring mod the ground is changed to a single ground for each headlight rather than the way Datsun originally did the wiring. The original 240Z wiring would not work with LED bulbs because the post normally used for ground was power and high/low beam was controlled by switching grounds. See this thread;

 

Edited March 12, 2020 by w3wilkes

[ETI4K]

Well if that won't teach me to stop thinking while on pain meds (recovering from shoulder surgery) - It certainly seemed okay yesterday. ?

CO: I was looking at the diodes to suppress arcing from the load when the relay opens which would reduce contact damage.  Not sure I ever used one across a coil, but I certainly agree coil inductance can cause trouble in certain circuits.  My oversight on the 20A feeding both - I agree with you.

Thanks for the corrections!

[Captain Obvious]

9 hours ago, ETI4K said:

CO: I was looking at the diodes to suppress arcing from the load when the relay opens which would reduce contact damage.  Not sure I ever used one across a coil, but I certainly agree coil inductance can cause trouble in certain circuits. 

LOL. Glad to help. Here's one more.

The only time you need to suppress the arcing from a load is when you have a load that creates an arc. Headlights aren't typically one of them.

The most common load that causes a problem is an inductive load. That's the exact reason they put that diode across the relay coil. That coil is an inductive load. Headlights are not.

[ETI4K]

I agree re headlights not inducing much arcing, especially not a concern with the very low switching frequency - a few times a night, maybe?  Although, I have seen relay contacts weld up on a motorcycle headlamp flasher (a safety add-on that had a small market) for that very reason (but that was about 100 years ago, I think).

But couldn't the same thing be said of the flyback energy on a coil being controlled, not by a solid-state device, but a mechanical switch?  There's no real switching noise, and the flyback energy from a 200mA(?) coil load couldn't have any negative impact on the 12V power circuit.  Although I suppose it could make its way through to an ECU or solid-state regulator.

Questions, not assertions.  Comments always welcome

[Captain Obvious]

4 hours ago, ETI4K said:

But couldn't the same thing be said of the flyback energy on a coil being controlled, not by a solid-state device, but a mechanical switch?  There's no real switching noise, and the flyback energy from a 200mA(?) coil load couldn't have any negative impact on the 12V power circuit.

Same thing cannot be said. The bigger the L, the higher the spike, but the same physics still applies.

[ensys]

 

Well folks, it's gratifying to see some feedback. Education never ends...

First, some comments:

- The relay diagrams were lifted from actual relays, chosen purposely with the integrated backfeed buffers (diodes, etc.). I acknowledge that the buffers may not be necessary in this case, but I like the sense of extra finesse.  Also, my decision process was influenced by a more intimate knowledge of my own driving habits that employ a more frequent use of beam-switching than may the norm for many. Low-to-hi-and-back-again, plus flashing, added to simple on-and-off, adds up, by my reckoning, to quite a few cycles during typical night road work.

- Same principle at work with the choice of wire ga. As I am not planning production of umteen thousands of units, I like to afford myself the luxury of over design in wiring.

- I concede that the fuse choices are probably over-kill, again out of caution (15a would likely be a still prudent choice), but easy replacement makes refinement simple.

Finally, I will note that since posting this postulation, I have made a few alterations in the design, including a change to an 8 pole relay to control the hi-low circuits, and a 4 pole to control on-off. Of course, this flow required several routing changes, all devised to more accurately emulate the operation of the original configuration of inter-related column switches.

 I'll post a revised presentation as soon as time allows.

I thank you for your interest and valuable critiques.

 

Edited March 19, 2020 by ensys

[ensys]

 

For your consideration; Plan B

I believe this configuration will preserve all the original switch and indication functions with the least alteration of the (e) wiring.

I invite your comments.

 

[ETI4K]

I'm not clear on how the primary relay is controlled.  My understanding is 12V (always hot) comes into the switch on pin 7, and 12V is supplied to the headlamp fuses on pin 6 when the switch is ON.  You've interrupted that connection with the insertion on the primary relay. 

So if the relay is not energized and the switch is OFF, 30-87 is closed providing power to the headlamps and pin 6, with pin 7 essentially at ground potential. 

If the switch is ON, pin 7 is hot which energizes the primary coil, opening 30-87.  But as soon as that happens, power is removed from pins 6 and 7 de-energizing the coil. 

I feel like I'm missing something.

 

[ensys]

 

Mr.K:

Well, I think you'll find that the hot in is at pin 6, arriving on the red/wh directly from the fusible links.

The red out of pin 7 goes to the fuse box where it feed the R and L headlights. I interrupt this feed to energize the Power Rely coil when HL are selected from the switch. This event then directly connects the hot feed from the F.L. to the feed to the HL at the fuse block

Also, the Power Relay is N.O. as shown. Energizing the coil closes the switch, powering the H.L.

 

This would be a good time to note that despite the fact that the (e) fuse deployment should continue to provide sufficient circuit protection, I am mulling the idea of introducing additional fuse(s) within the added circuits. Call it the spirit of suspenders and a belt....  Any thoughts?