Yet another trip through the bad gauges

[marc]

Friends, I know that there have been extensive discussions of building a home brew solid state alternative to provide 5 volt to the gauges in jeeps. Just did the testing to establish the ground for my gauges is intact. Hunting for a solution, I have run into a variety of 12 Volt to 5 Volt converters differentiated by a variety of amperage outputs. Not car type power supplies. One example is posted below.

https://usa.banggood.com/DC-DC-Converte ... rehouse=CN

These are used to provide 5 Volt to everything from LEDs to radio controlled model aircraft. Unfortunately, determining if the electronics of these devices is applicable to the gauges are beyond my level of expertise. Does anyone know the total load drawn by the three gauges? Is there a way to use them to power the gauges?
Marc

[sirrus]

While waiting for someone with measurements to chime in, I’ll give my theory

Given that people were using 7805 to step down 12v to 5 and those things are getting hot anywhere near 750mA with even less voltage drop, I think you’re well within 3A limit of UBEC from your link. Good idea about using that module - those things should be easier to wire in than IC like 7805 and they’re probably available in any hobby/model shop for a few bucks

[tgreese]

What's the issue that would suggest this other part? A switching supply will still consume some power besides what it sends to the gauges. This will require a ground to function, just like the 7805.

This "DC-DC convertor" is a switching power supply. It takes the 12v DC input and chops it (turns on and off) into square wave AC at a high frequency. It then uses a transformer (inductor) to convert this high frequency AC to a lower voltage. The resulting lower voltage is rectified into DC. Switching supplies are efficient but make a lot of rf noise. The supply in your computer is a switching supply.

If your switching supply has 4 wires, two in and two out, I expect they must match polarity (no isolation). That means two of the wires are tied together as ground, and you have the same number of connections (3) as the linear regulator. The 7805 does need the addition of a capacitor on the input and the output. (You can probably leave out one or both the capacitors - read the datasheet.)

When you have a vehicle that's powered by a tiny battery (drone? model plane?), power must be used efficiently. A switching supply will be more efficient than a linear supply, ie less power lost as heat. The 7805 linear regulator throws away the excess voltage as heat. However, in a Jeep, this heat loss from linear conversion is not significant.

I don't see how a little switching supply brings much to this issue. The 7805 doesn't even get warm in this application. Driving two gauges should be something like a 50-100 mA load. Nearly nothing at this voltage. No fewer connections. I guarantee that a generic switching regulator from the Shenzhen marketplace will have a much shorter lifetime than the linear regulator 7805 in this application. The parts are easy to find and cheap too.

46c for a name-brand regulator (ON Semi was spun off from Motorola).
https://www.digikey.com/product-detail/ ... -ND/919333

2 capacitors at 42c each
https://www.digikey.com/product-detail/ ... -ND/286789

Prepay your order to Digikey (send them a check) and they will cover shipping. An honest $1.20 total plus tax.

[marc]

Don't know what it brings to the discussion but if I can walk across the street and get a converter from my neighbor who is building himself a fleet of RC model aircraft, it could put me days ahead on my goal of getting this J10 functional prior to when the rains start here in earnest.
Marc

[tgreese]

Suit yourself - it should work. The linear regulator will be more reliable. You can get 7805s through Amazon by Friday, if you are willing to pay more.

[marc]

Crazy world we live in, you can't get electronic components off the shelf anywhere in Seattle, nor can you find those small power converters in town. Used to be down the street from Radio Shack and up the street from Radar Electric. The project has run into a setback, likely delayed anyway, so I may well go the transistor route.

[tgreese]

Suggest you get your parts from Mouser or Digikey. That's where I've bought parts for two decades or so. If you order online and pay for shipping, you can get your parts in a few days. Both companies handle small orders well, and welcome them. I prefer Mouser, since their site is not affected by my ad blocker (Digikey wants to place trackers, and their site depends on them).

Seems like the local electronics parts brick-and-mortar stores just aren't profitable any more. Radio Shack went under when their business model fell apart. The margin on electronics parts from there was huge, when you compare with the retail prices from an online supplier like Mouser or Digikey.

Last time I was in Radio Shack and bought an actual electronic part must have been 10 years ago. Their selection of stuff had shrunk to a few cables and assortments on pegs, and a big cabinet of drawers - far from the heyday when all this stuff was out in bags on pegs.

Too bad. Part of their company was Antennacraft, which supplied some great pre-made antennas. Currently have their big Yagi for low-band TV on my roof, and there's no direct replacement on the market now. Eventually the aluminum will corrode through. By that time, maybe low-VHF TV will be gone and I won't have the need. Ah well - into each life a little rain must fall.

[letank]

Don't know what it brings to the discussion but if I can walk across the street and get a converter from my neighbor who is building himself a fleet of RC model aircraft, it could put me days ahead on my goal of getting this J10 functional prior to when the rains start here in earnest.
Marc

no more radio shack or tv repair store,if desperation hits, there is real store 20miles away, almost worth a bike ride journey, but with covid-19 and the smoke from the fires on the west coast, cracking open a beer, or uncorking some adult beverage are the preferred choices lately.
Even going a few blocks away to get an alternator is not a success story... last time I saw an FSJ at the junkyard I grabbed as many parts that I could carry... even little screws of odd size, once I grab a transfer case and drive shaft... welcome to the madness...

[marc]

I was very close to getting this j10 to full functionality but then a setback or two, exhaust check valve broke off, pulled a groin muscle which keeps me from getting under the truck to deal with it. That has left me with the standup projects, nonworking triad of gauges and the valve cover gasket. Confirmed that it was not a ground issue and pulled the gauge cluster. There were a couple of suspicious signs, it appears that the plastic lens had been damaged and temp/fuel display pushed a bit back, the face of the gauges show signs of damage and the plastic brake light container had melted a bit. The faces of the gauges have broken elements, see the photograph. Hard to tell but both gauges have the small diagonal pieces broken. I am wondering if the CVR is damaged or if the gauges themselves have been damaged> Any way to do an off/on test of the gauges and cvr?
Thanks, Marc

[marc]

Looks like I joined the bad CVR club as I was able to use a stack of D cells to drive each gauge. Given that my project is delayed as I heal from a pulled groin, it looks like I will go the 7805 route. Marc

[Bruduf]

I just put in a new temp gauge that if I understand correctly has the resistor built in fixed all my gauges. Am I missing that there has to be another resistor too?

[candymancan]

Don't know what it brings to the discussion but if I can walk across the street and get a converter from my neighbor who is building himself a fleet of RC model aircraft, it could put me days ahead on my goal of getting this J10 functional prior to when the rains start here in earnest.
Marc

no more radio shack or tv repair store,if desperation hits, there is real store 20miles away, almost worth a bike ride journey, but with covid-19 and the smoke from the fires on the west coast, cracking open a beer, or uncorking some adult beverage are the preferred choices lately.
Even going a few blocks away to get an alternator is not a success story... last time I saw an FSJ at the junkyard I grabbed as many parts that I could carry... even little screws of odd size, once I grab a transfer case and drive shaft... welcome to the madness...

Same here.. my storage unit is full of switch. Screws. Knobs. Everything you can think of. Starter. Alternator. Grill. Dash pad. Even carpet and leather peices from the seats. Meaning like i cut good leather off seats so i can patch mine in case. Or spare carpet peices.

I took a 229 transfercase and pushed it to the pay booth with a baby stroller ( lol) i have it because ive seen alot of threads of the 229 viscous coupler going bad. Since they dont make em. Then i have a 229 with a good one ( based on the pink fluid anyway) for mine