Alternator Question: 2017 4Runner

[Okie Preacher]

I have been having a bit of intermittent trouble with the refrigerator in the 4Runner.

When running on the house battery it would run fine for a while, but intermittently stop cooling (fan running, lights on). I brought her into the house and plugged her into the 110V and she purred for 12 hours running perfectly…so I don’t think it is a problem with the fridge.

The start battery tests 12.6 with the engine off and 13.4 with the engine running at idle. Chasing through the system, the house battery tests 12.45 with the engine off and 13.24 with the engine at idle. The outlet at the back of the 4Runner tests exactly the same as the house battery—large gauge wire so no drop from front to back.

I ran it up to the auto parts store. Their test indicated a problem with the voltage regulator in the alternator, not allowing the batteries to fully charge. I never know whether to trust their tests as they have a vested interest in selling parts. On the return home I attached a charger to the house battery first and it indicated the battery to be 65% charge, and the start battery to be at 80% which gives a little weight to their diagnosis.

Fully charged, the refrigerator is now running well making me think we have been dropping voltage to a point causing her to trip off.

In the experience of the crowd, is it time to try a new alternator in an attempt to keep things fully topped off?

 

[DaveInDenver]

Those of us with Toyotas have a pretty well known issue with our alternators. Basically, yes, they are set to a low voltage and are not aggressive charging systems. Yours is perhaps lower than normal but not a lot. Replacing the alternator might fix it or might not change anything.

Research how to voltage bump your Toyota alternator and you'll get any number of descriptions and solutions. There's not really one universal way to do it but typically it involves using a diode in the Alt-S circuit. Alt-S is the alternator sense line and it has a 7.5A fuse in the main under hood fuse box. By placing a diode in the circuit you introduce a voltage drop that tricks the alternator into increasing its output voltage.

 

[Okie Preacher]

Those of us with Toyotas have a pretty well known issue with our alternators. Basically, yes, they are set to a low voltage and are not aggressive charging systems. Yours is perhaps lower than normal but not a lot. Replacing the alternator might fix it or might not change anything.

Research how to voltage bump your Toyota alternator and you'll get any number of descriptions and solutions. There's not really one universal way to do it but typically it involves using a diode in the Alt-S circuit. Alt-S is the alternator sense line and it has a 7.5A fuse in the main under hood fuse box. By placing a diode in the circuit you introduce a voltage drop that tricks the alternator into increasing its output voltage.

Thank you, Dave. I learned something this morning. With your information, I am guessing my alternator is probably fine--just running on the low end of the acceptable range.

A quick search turned up this product: https://www.arclightleds.com/collec...ooster-5th-gen-4runner-fj-cruiser-pg2tb-brs6a. A fairly elegant solution to the problem, but they are out of stock into the new year. Understanding that I am convinced electricity is black magic and I am not a practitioner of those dark arts (to be interpreted as "I am an idiot when it comes to electricity and electrical systems.") would you be kind enough to point me to a link of the diode you described above. It sounds like it is a plug-and-play affair, and might offer the house battery the bump it needs.

 

[DaveInDenver]

Forgot one thing to mention. You have a 2017 4Runner and you may have a smart alternator. I don't know that for a fact, though, just a possibility. Although based on the link to the device you provide I'm inclined to think the 4Runner didn't get a smart alternator until 2020. That device will do the voltage bump and it does look like a nice product. I suspect it would be fairly pricy if it was not out of stock.

I've tried two ways to solve this on my truck.

One approach I took is to just replace the fuse with a diode fuse. This is nothing more than a diode that's been molded into a plastic case that is the size and shape of a fuse. They're used sometimes by OEMs to solve wiring harness problems.

The one I used is a Ford part number 4F2Z-14A604-AA. Think I paid about $8 for it.



In the Tacoma the Alt-S 7.5A is on the left side under the 10 and above the 20. The diode fuse is marked 1.0 in this case, which is the max current the diode inside can tolerate I think since from what I can tell it's simply an 1N4001 molded in there. I only include that detail in case someone technical is interested. The one I have gives about 0.6V of bump but it may be somewhat higher or lower depending on the individual part variance.



Alternatively I've been tinkering with making my own fused solution using an Add-A-Fuse tap and discrete fuse. In this case I tried a Schottky diode, if memory serves a 1N5404. The reason for this one was that it has a very low forward voltage (e.g. bump), something like 0.3V. It was an experiment and this small of a bump normally isn't worth the trouble.





The real important thing about using a diode is the direction is critical. In the right way you get a voltage bump. Put in backward you get no charging at all. So if you're not comfortable with diodes and electrical systems you need to make sure you watch the details if you're following a description from the Interwebz.

 

[Okie Preacher]

Thanks again, Dave. The Ford diode is ordered and will be here in a couple days.

 

[Delloro]

Thank you, Dave. I learned something this morning. With your information, I am guessing my alternator is probably fine--just running on the low end of the acceptable range.

A quick search turned up this product: https://www.arclightleds.com/collec...ooster-5th-gen-4runner-fj-cruiser-pg2tb-brs6a. A fairly elegant solution to the problem, but they are out of stock into the new year. Understanding that I am convinced electricity is black magic and I am not a practitioner of those dark arts (to be interpreted as "I am an idiot when it comes to electricity and electrical systems.") would you be kind enough to point me to a link of the diode you described above. It sounds like it is a plug-and-play affair, and might offer the house battery the bump it needs.

He is sold out. He just did a run a month orc2 ago, might be doing another one.

HKB sells a voltage booster too.

 

[ConcordCarlos]

This is what I use in my 08 GX470.

HKB Electronics

The Alternator Voltage Booster was the first of its type on the market and is the only unit available that was has been purpose built for alternator voltage boosting.

www.hkbelect.com

 

[Deleted member 13060]

There are so many 4 Runners and other Toyotas running dual batteries and fridges with the stock charging system that the chances of the "Toyota" portion of the system being the problem are pretty much, slim and none.

I'd check the dual battery system and unless it's a Redarc DC to DC I'd make sure the two batteries were new and the same size, rating.
4ga min cable to the house battery with a double checked, super clean ground. Preferably near the start battery on the engine block or stock fender ground.
10ga min wire to the fridge.

After 28 years in the auto repair field, 90% of electrical issues are ground issues, esp on aftermarket stuff.

YMMV RON