Troubleshooting Renogy DC-DC charger. Is there anything else I can try?

[Martinjmpr]

Posting here because this board is the fount of knowledge on power and electrical stuff as far I can tell.

If you've seen my other posts you know that for the past 5 years I've been running my 12v fridge off of my "redneck Jackery" power box. The power box is simply a trolling motor box with a 12v battery in it. In January I upgraded to a LiFePo.

To charge this contraption, I have a Renogy 20A DC-DC charger in the back of the truck's cab. I ran an 8AWG cable from the battery (fused at the battery end, of course) under the truck and up through a hole in the cab to the rear of the cab behind the back seats. That's where the DC-DC charger has sat for the past 5 years (installed in Spring 2020.)

Up until our last camping trip, this setup worked fine. With my new LiFePo battery having a Bluetooth display, I could monitor the battery's state-of-charge from my phone.

So last week we were camping, first at Bandelier National Monument (Amazing, BTW!) and then near Red River, NM.

It was HOT. I think that may be relevant?

Anyway, around Thursday of last week, the battery just stopped charging. At first I thought I had incorrectly crimped a cable and swapped in a known good cable, but that wasn't it.

Then I got out the multi-meter and discovered that the DC-DC charger was not putting out any current.

I was able to limp along using alternate methods to keep the battery charged and now that I'm back home I was finally able to do some proper troubleshooting.

So, here is what I did and the results:

Tested cable from the battery to the cab. Result: 12- 14+ V going in to the cable (with engine running.) So I know the cable and the fuse are good.

Connected the DC-DC charger and it powered up (green "pilot" light came on.) Tested output voltage, and it also came out showing 14+ V, but the pilot light was flickering and varying in intensity.

Connected to the power box and immediately the DC-DC charger shut off. Yes, I double checked all the connections on the power box, no reverse polarity.

Now the charger won't come on at all. What's even weirder, when I connect the charger and then check voltage on the "input" side, it only shows 2v? How can that be?

Photos attached showing the multimeter reading when the DC-DC charger is connected and the reading when it is just the cable terminals.

Bare terminals showing 12v (engine was off.)



Connected to Renogy charger. Showing 2v?



What would cause this to only show 2v? Seems like even if the charger is 100% dead I should still be reading the full voltage from the battery, right?

Anyway, I've done just about everything I can think of. At this point I seem to have good power going to the back of the truck and the only conclusion I can come to is that the charger has failed after 5 years. Given that it sits underneath the seats and that it's been getting bounced around for the past 5 years, I probably shouldn't be surprised.

So unless there is some kind of reset I can do or some other thing to test, can anyone recommend another DC-DC charger in the 20A range?

And any thoughts on ways to mount it to minimize damage from either bouncing or excess heat?

Thanks in advance!

 

[TwinStick]

I am not an expert nor an electrician. Having said that this is what I know.

Heat is the enemy of ALL THINGS ELECTRONIC. From stereo amps to 12v refrigerators to battery chargers and dc to dc chargers. The cooler they run the longer they will last.

Wire size is extremely important as well. And, to some extent, it can add to making things run hotter if it is not big enough. When in doubt, go 1 or 2 sizes bigger.

Also, smart alternators can add a whole new twist to things. From what I've read , smart alternators are designed to only actually be operating 20 -35% of the time. Depending on how big (amps) your dc to dc charger is and how hard its working, it has the capacity to drastically reduce the life of the smart alternator. I watched a YouTube video of someone much more knowledgeable than me, who did a test on his 2024 fullsized Denali with an 800 watt dc to dc charger for his power station.

The computer said it was operating at 85% - 100% of his smart alternators capacity. So you can see how that would shorten the life. Working harder results in more heat, and wire size may or may not make a difference in his particular case but thicker wire with more strands would make it as efficient as possible.

I hope you figure it out but my unprofessional opinion is that it may very well be somewhere in all that. Oh, and don't be afraid to use a fan.

Good luck.

 

[Verkstad]

Your symptoms are pointing to a resistive connection in the 8AWG circuit.
Under no load, you read 14V, as you connect the charger, it drops to 2V.
Double check crimp connections, solder joints etc.

Maybe try this.
Leave the charger connected and verify the 2V reading.
With the meter still connected, bypass the fuse holder. Observe if voltage comes back to normal.

 

[Martinjmpr]

Your symptoms are pointing to a resistive connection in the 8AWG circuit.
Under no load, you read 14V, as you connect the charger, it drops to 2V.
Double check crimp connections, solder joints etc.

Maybe try this.
Leave the charger connected and verify the 2V reading.
With the meter still connected, bypass the fuse holder. Observe if voltage comes back to normal.

Thanks, that’s a good recommendation. I actually just changed out the fuse block a few months ago so that might be part of the problem.


Sent from my iPhone using Tapatalk

 

[DaveInDenver]

Try measuring the resistance of the input on the DC-DC, both polarities. If your meter does it I'd also check the input using the diode check function, also both polarities.

What you're showing looks odd and what I'm asking is to eliminate that it's the DC-DC. It's possible the DC-DC did suffer a failure and those tests are looking for unexpected values. There may be a reverse polarity protection and even if you didn't hook it up backwards heat or voltage spikes from starting can cause that circuit to fail.

Another option is to just connect the DC-DC to another battery. It doesn't have to actually be an alternator to test. It may not start charging but it should power up with any voltage higher than probably about 10V.

What @Verkstad is asking is I agree a more likely case, though. This being that you have a large voltage drop in the cable so you're not actually seeing a DC-DC issue but it's malfunction is a symptom. That it shuts down immediately could just be the under voltage protection circuit or just it simply turning off due to low voltage.

Say your DC-DC wants 20 amps and you have a bad connection, partially blown fuse or wire that's broken but no gap (e.g. the conductors are touching inside the insulation). Then let's assume you have 14V at the source (battery, alternator). If you have just 600mΩ of resistance in the cable you'd get 12V of drop at 20 amps.

If the resistive issue is worse, perhaps a few ohms the 12V drop could occur at a couple of amps, the DC-DC itself requires some current to function even if it's not active. I doubt that is very much power. Say it's 200mA to just turn on (this is just a from thin air WAG) a resistance of 60Ω would be required and that should be easy to find.

I'd check the cable closely. Look for kinks or places it may have rubbed on sheet metal edges. You may not be looking for a major break but a partial one. You can use the continuity function on your meter to help you. One option is to disconnect both ends of the cable run, short one end, measure continuity across the other end and run the length, jostling and moving the cable listening for the beep to stop.

Yeah, when something working suddenly fails I'd also work backwards from what changed. A new fuse block means you disturbed wires, perhaps new crimped terminations and added a device that may have defects.

 

[burleyman]

Quick and dirty: Ready a replacement fuse. Brush the two wires together. There should be sparks and a blown fuse if you leave the wires connected too long.

Another way: Use a fuse with a lower rating than the one installed. Connect your wires to each side of that lower rated fuse. It should blow.

My favorite: Purchase a 12v trouble light tester or make one like the one below. Use it instead of a meter. Unlike the meter, they load the circuit.

If it doesn't illuminate, use a jumper across all fuses and connections and look for illumination.

 

[Martinjmpr]

So here's the update as of this mornings testing:

I went out and connected the ring terminals at the fuse block to the same terminal (bypassing the fuse itself.)

With the engine OFF it is showing 12+ v:



So then I started the engine. Now showing 13+v and getting a strong green pilot light on the charger:



The charger continued to show a strong pilot light.

So then I connected the battery and as soon as I did, the pilot light dimmed, then started flickering. I could hear audible clicking and the fan turning on and off in the charger. After a few seconds the pilot light went off and didn't come back on.

After that, showing the ~2v.



Given that this system has worked more or less flawlessly for the past 5 years (minus some glitches that were my fault), as well as the sudden failure, does this not point to the charger itself? Wouldn't a loose wire or a short circuit (grounding to the body through the hole where it passes into the cab) be more likely to cause either an intermittent failure or a total failure with no voltage shown regardless of whether the charger is connected?

Short version: I seem to have power until I put a load on the charger, then it goes to ********. Doesn't that point to the charger as the culprit?

 

[DaveInDenver]

No, it doesn't necessarily indicate the charger. I did a poor job of explaining. What I'm suggesting is that the voltage drop could increase with load.

When you first turn on the DC-DC it's a low draw, just the internal consumption, a few watts perhaps. This is the power the device itself requires to run itself, the microprocessor, the Bluetooth, etc.

You need to measure at both ends of the feed. I bet even when it's on but no charging load there's still measurable voltage drop in your wiring. At just on you should see the same voltage almost exactly, within a few millivolts. What are you seeing at the alternator/starter battery/fuse block when you measured those 13.32V and 12.38V values?

When you connect the load battery that current is passed through, only a small amount is lost internally in the charger but the high current still has to travel over the feed circuit, giving you the high voltage drop.

It still sounds like you have a some resistance in the feeding circuit. It would seem low, probably well under 1 ohm, but enough that the voltage at the input to your charger is too low to stay on. Compromised wire, maybe a bad crimp or insulation under the terminal crimp, loose nut or bolt. Could be the fuse block is broken or the internal bus is bad or undersized.

Now, yes, the charger could be flaky. But I would eliminate the power source and feed before making that assumption. You could power it with jumper cables, bypassing your whole distribution as another option.

My presumption would be the charger would protect itself so if it fails it would not power on at all. Even that wouldn't necessarily mean it's dead. There's probably internal fuses, so there's a chance it could be repaired. The way it's acting doesn't immediately sound to me like it's the problem, though.

 

[Martinjmpr]

OK, I think I may have isolated the problem.

I thought I'd try checking resistance to the whole cable from the battery to the cab.

I'd been spending all my time looking at the + terminal (with the fuse.)

But when I went to take the negative terminal off the battery, this is what I saw:





That black cable is the negative cable to the power to the charger. I'm pretty sure it's not supposed to look like that.

From what it looks like, something must have happened to cause that to melt, either excessive heat under the hood or perhaps a short circuit? Not sure.

Next question is: How to bypass this section of wire? Should I try butt-splicing it? Some kind of terminal? I could cut the wire behind the damaged portion, put a ring terminal on it and then run another short section to the battery, would that be OK? I am really reluctant to pull the whole wire out because it's a single piece of wire that runs all the way to the back of the truck so it would be a massive PITA. But if that's the only good solution, I'll do it.

 

[DaveInDenver]

Yes! That's exactly the sort of thing you're looking for, it make sense.

I'd guess the way and length of insulation that melted that the cable got hot. Are you sure of the size and loads it carries? One reason this can happen is it's carrying a load you don't expect, too.

You know how the harness you get with a ham radio has two fuses, one on each side, when it runs all the way to the battery? That's so it's protected if one side carries a current for another circuit. It's usually the ground side where this fault happens when another circuit that uses the chassis ground loses it's connect to the chassis. The current wants to return to the battery and it'll look for an alternative path.

There's other possibilities, a short to a heavy positive connection or the battery positive itself. You might have to think like an electron, be the electron.

With a big cable like that trying to butt splice is going to be tough to do right.

You could add a negative busbar in some way?

It's also possible there's other places the cable was overheated or damaged.

Pulling a new run is probably the safest thing to do.

Is that even marine or welding cable? It looks like PVC and maybe fairly low temperature PVC at that.

Not sure if many people realize that the temperature rating is above ambient. So under the hood if you use 75°C insulation and it's already 40°C just from the engine heat you only have a 35°C delta before your wire melts through. That may be a problem if the cables are sized without enough margin.

Another possibility is that it just melted, maybe touched exhaust, touched the hood that was in the sun, etc.

 

[Martinjmpr]

Dave: I have an extra Bojack fuse block (and extra fuses.) I can't think of any reason that WOULDN'T work. It would mean the circuit is fused on both the + and - sides but there's no down side to that, right?

 

[Martinjmpr]

OK folks (Especially Dave and Verkstad):

THANK YOU! Problem has been identified (damaged wire on the negative battery cable.)

Here is the underside view of the damaged negative cable (right at the terminal.) Pretty gnarly!



So I cut off that end and crimped a ring terminal onto it. Then to connect to the negative cable I used a very heavy (1AWG) cable that I happened to have on my bench (see, this is why I don't throw anything away. I made that cable, crimped it, and put heat shrink on it only to realize it was too short. But I didn't throw it away, it went into my work bench.)



And when I ordered the Bojack fuse blocks for in-line fuses, I ordered a couple of extra ones. So I just put one in on the NEGATIVE side. This is what it looks like now:



The fuse block that has the cover removed (with the wing nuts) is what I use for my "disconnect." When I don't want the charger to run (like when I'm not on a trip) I just loosen the wing nuts and remove the fuse, and it sits in my glove box in a zip loc bag with 3 extra fuses.

The final test was to hook it to the battery and see if it shows the battery being charged (using the battery's BlueTooth connection):



SUCCESS! 20.14 amps going into the battery!

So thanks again to all the folks here who helped. If it wasn't for you I would have just bought a new charger thinking my old one had failed, and then I'd likely be back here trying to figure out what was going on.

As far as future plans go, I still may consider upgrading the wiring to 6AWG, but I think replacing that cable would be a full day project for me (I work slow.)

In any case, the issue has been resolved and, again, thank you so much to the people who volunteered their time to help me figure it out!

 

[DaveInDenver]

Glad you figured it out.

Nothing wrong with a fuse in the negative. Like I say some accessory harnesses come with them and it's an extra layer to prevent excessive fault current on a negative run like may have happened to you. Some nuisance downsides, like now you have more fuses to check and carry spares. You'd size it just like the hot side, based on the gauge of the negative wire.

I prefer a crimped ring terminal over crimped butt connectors, but a crimp is a crimp is a crimp. It's about workmanship.

I find that a stiff length of a butt connector, particularly large ones like you'd use here, tend to have fatigue problems down the road. But your home's electrical service from the pole to your meter has them at the entry head, so that's just a personal preference on my part in vehicles and with careful routing and support needn't be overly concerning.

 

[Verkstad]

Fwiw,
Your last pictures show the name "Voodoo" on the 8AWG wire.
I suspect that stuff is copper plated aluminum. (Purchased thru Amazon maybe??)
Aside from large distribution/service entry conductors. Aluminum is bad news in any wiring system.

One seat of pants way to test if your stranded mystery wire is copper plated aluminum..
Strip and fan out an inch or so.
Heat that with a Bic Lighter.
Copper will just get redhot and oxidise.
After cooling off the copper will still have some strength & flexibility.
Copper plated aluminum will either melt away, or easily break & crumble after cooling.

 

[DaveInDenver]

Aluminum is bad news in any wiring system.

Why do you think that is so?

There are reasons why what you say is absolutely correct and, if true here, would help explain Martin's experience and potential for a future repeat.

Some vehicle OEM wiring is aluminum. Much of the grid is built with aluminum wire. This is done intentionally and for some of the same reasons (weight and cost). It's not automatically bad if the choice is done knowledgeably so the correct adjustments are made (sizing, mechanical support and terminations).

We without a doubt agree on the deceptive nature of cheap clad wire on Amazon and that you must not carelessly substitute aluminum in place of copper.

Part of the problem is that to meet the price it's poor quality, which can bite you with copper that's under gauge, junk insulation, oxidized, lacks enough strength and what-not, too. One can't just assume poor quality all copper is automatically better than properly represented clad, despite that I agree custom upfitting should avoid aluminum if at all possible.