Headlight Diode melt down

[Nadge]

2016 Ventana LE 4037.

I'm what you call a "Shade Tree Mechanic", having basic 12v electrical knowledge. I appreciate any help in trouble shooting my issue.

The OEM, DT04-4P-RT01 diode on my 12v lighting system of my 2016 motor coach, melted and only the headlights were lost.

According to the manufacturer's diode schematic, the diode is rated at 4amps, and -40c / 275c (257F) operating temp range.

No other issue of the light module was affected. Only the diode which supplies head light bulb current individually, through the headlight switch to the two headlights.
I purchased the same replacement diode as identified by part number on the OEM diode.I tested the new diode with the original bulbs and again with new Sylvania H13 55/60 W bulbs with same overheating results.

When I installed the replacement diode, leaving the switch off, no temp change to the diode occurred. I turned the headlight switch on and both came on. Both low beams and then high beams tested ok.
Using my IR temp gun, I watched the temp of the diode immediately heat up and I allowed the temperature to reach 235F before I shut the switch off, so as not to exceed the rated operating temp of 257F of the diode. Shutting off the headlight switch stops the temperature rise.
The lighting module is up stream of this diode and no temp increase was observed in this module, while the diode was heating up. All lights controlled by this module, operate properly..

I measured 12v supply to each supply leg of the multi diodes within the DT04 *and then 12 v at each headlight sockets. Two wires in, two wires out of the diode.

I have since purchased two new Sylvania H13 bulbs and I'm told each bulb draws 3.89 Amps. That tells me the diodes 4.0 rating is within normal operating range, albeit very close to top end.
I don't have an "Ohm" line tester to test actual amp draw but will find a friend who may have one.

That is the extent of my trouble shooting process and I reluctantly may have to find a local technician to solve this issue.

More lost RV time.

Thank you for your time and information.

[Jim_HiTek]

ET here with 60 years practical experience. When designing a circuit, engineers spec diode ratings like with all passive or active components. At 200%. So if the circuit will be drawing 2 amps continuous, typically, we'd spec a 4 amp or GREATER rating. In your circuit, since you've changed the headlight it's now required to source 3.89 amps, those diodes are underrated and at the LEAST need a large heat sink...which I doubt that plastic assy provides.

The P/N you show for that part, is $53 in single quantities. That's outrageous for some diodes so what I'd do is buy some 10 amp or greater 50 volt diodes for $0.50 each and wire them in place of that expensive part. Here's one example of 20 diodes for just $5 (if you have an electronics parts supplier in your town, you can probably pick them up on Monday for not much more money, you just ask for a silicon diode 15 amp @ 50 Volt or greater)...Blocking diodes


Then you just cut that diode block out of the circuit and crimp the diodes in. I'd cover them with heat shrink but I'd also leave the wires long on the diodes because that's part of their built in heat sink.

This all assumes you're fairly well satisfied there's no weird partial short somewhere in the bulb circuit. A wire squished by a piece of grounded metal somewhere.

[Nadge]

Currently trying to figure how to remove the 4 gang rocker switch plate without having to remove the whole dash nor break plastic parts. I removed the dash cover plate above the odometer cluster but the switch plate backside is not visible although more accessible than from beneath.

[gatorb8]

every shade tree mechanic (your words! . )should have a clamp on dc amp meter

that would help determine if you over - currented (word? ) your diode

["007"]

Not sure what your trying to do but maybe this thread may help.

[Dutch Star Don]

One of the ways to get past minimally required wiring or diodes is to use a relay. I'm guessing you're trying to run headlights that are drawing too many amps for your system. Simply run some larger wiring to the lights from the the large 12 volt supply in the run bay (bay under driver's window). Use the current headlight wiring to trigger the relay that is connected to heavier wiring.

[Waiter21]

A 60 watt bulb at 12 volts will draw approximately 5 amps ( I = P/E) (60watts/12 volts)

I'd say you need to at least double the amp size of the diode. As mentioned by others, consider a relay(s)

[Nadge]

What I'm trying to do, is determine why the headlight diode melted in the first place and now with a newly purchased, same part numbered diode replacement, is heating up to melt temperature?
Everything is OEM from Newmar.
I purchased this RV new, no prior lighting issues with running lights, directionals etc.

I was told the OEM Sylvania H13 55w 12v bulb draws 3.7 amps. Yes, I did install brand new same 55w bulbs with same overheating of diode issue.The OEM diode is rated at 4 amps, so why the melting of the diodes?

Does Newmar offer tech support for trouble shooting such an issue?

[Nadge]

would a "clamp on" amp tool, read the small amp draw of a headlight bulb of 4 amps?
If you say yes, I'll headout and purchase one to help me solve this issue. Thanks

["007"]

Did you do a search for your problem? == search

[gatorb8]

Originally Posted by Nadge

would a "clamp on" amp tool, read the small amp draw of a headlight bulb of 4 amps?
If you say yes, I'll headout and purchase one to help me solve this issue. Thanks

yes, make sure it is a DC clamp on amp meter

[Nadge]

Finally resolved the diode melt issue.
After replacing both headlight bulbs with new H-13 bulbs, and the headlight switch and still had diode heating up to 235 deg F.
Checking with Freightliner about bench testing the LCM, he said there was no bench test I could perform.
Sooo, the last item in this simple lighting system remaining to replace was the LCM.

Speaking with Freightliner about purchasing the LCM from them, I was informed that a purchase could only be made through an authorized dealership not direct from Freightliner.

I priced out two dealerships and the first one quoted me $725 plus shipping and handling and mailed to me.

The second quoted me $575 plus S&H.

Bought the $575 one, (smart of me, Huh) installed it with fingers crossed and no problems of over temping diode occurred. Problem solved for just under $695.

What ever happened to the $3.95 headlight switch???

[Nadge]

Up date to Head Light diode melt down.
After replacing the LCM, the headlights came on and the diode did not heat up for the 10 minutes I tested it for.
I presumed the fix was in.
I didn't use the RV for 6 weeks or so.(We usually only travel during light hours and park).This particular trip home we were 80 miles from home and decided to travel at night. As dusk turned to dark I noticed the roadway wasn't lighted very well since my fog lights being on, provided enough roadway light until I recognized the lack of headlight issue.
Sure enough, at some point in time my diode had failed once again.(Murphy is still around).
Since I had replaced all the components within the headlight system that I believe could have been the issue, ie: H-13 55w Sylvania bulbs, HL switch and finally the $575 LCM board.
I have an appointment with Newmar on Nov 09, 2020 and will add this issue to my other issues for them to hopefully resolve.

And yes, I certainly will allow enough travel days of daylight hours to arrive at Nappanee safely.

Safe motoring everyone.

[Arch Hoagland]

Do you have the schematics for your headlight system?