Adaptive Charging Upper Limit

[KYSilverado04]

Background Info: (TL/DR) at the bottom

I've got a little bit of a strange question and the answer may be that it's simply not possible, but it never hurts to ask. I have a 2011 GMC Sierra with the high output alternator option. I have recently installed a power inverter under the rear seat so my kids can plug in all their electric gadgets while rolling down the highway. The inverter is turned on and off with a relay with the ignition switch and everything works great..... until this morning that is.

This is the first time I've driven the truck on a "cold" morning (~48?F) since I have installed the inverter. As is usually the case on cold mornings with most vehicles the charging voltage is higher than it would be when warm. When the charging voltage climbed to around 15v, or a touch higher I don't have an exact number, the power inverter started squealing due to too high input voltage. As it is mounted permanently under the rear seat I don't have a good way to just turn it off, and I wouldn't want to use that as a solution because there is a very good chance it will be used on a cold day at some point. I feel like on even colder mornings, which is a very real possibility here, that it will only become more common. So the best answer seems to be to lower the voltage to the inverter a touch. I'm posting here due to the fact that the truck has the adaptive charging, I was hoping a software solution might be available. I'm looking at the tune and I see a few max voltages but not any kind of overall system voltage upper limit clamp. I might can tinker with the duty cycle and get a lower number but I feel like if I had a high electrical load that might hinder charging. So finally the question:

TL/DR:
Is there a way, in software, to put an upper limit on the charging voltage? Currently it can exceed 15v and I would really like to clamp it at around 14.9v.



Thanks!

Edit - If I'm understanding the verbiage correctly in the software, the voltage is actually controlled by the BCM and the ECM can override that if required, thus there may not actually be a way to lower it. Can anybody confirm or deny?

[10_SS]

Take the inverter apart, cut the wire going to the buzzer.

[KYSilverado04]

Take the inverter apart, cut the wire going to the buzzer.

The thought crossed my mind but I can't. To me that's no better than just removing the bulb or turning off error reporting for a check engine code instead of correcting the problem.

A circuit could be built to limit the voltage using a varistor but my knowledge of their behavior is insufficient at this point to know if it would work or cause more problems. I'm doing more research.

I found a device that plugs inline with the alternator and allows you to manually specify a charging voltage but that bypasses the benefits of the adaptive charging entirely so that's also not really the best answer. An inverter with a higher upper limit would also do the trick.

[goodwrenchdave]

Is this a high power inverter?
Where are you getting the voltage readings? the reason I ask is because never heard an inverter complain from 15 or even 16v input.... but they don't like unsteady or weak inputs. Seen a lot of sloppy wiring-connections at battery terminals, bad grounds etc.
It is not uncommon for GM alternators to charge slightly over 15v. If there are weak batteries, high resistance connections- the problems can increase.
You inverter ground should be hooked up to chassis. and positive directly to battery with the proper gauged wire. Relays are only good for low power inverters - amperage (current) need rise quickly even on small inverters - i prefer solenoid type disconnects unless your dealing with very low power inverters

[KYSilverado04]

I will attempt to answer your questions as best I can.

1. It's not a particularly high power inverter, 400w continuous, 800w peak.

2. Voltage readings are a bit of a guess but let me try to explain. The dash gauge is analog of course and anybody's guess. The inverter itself has a voltage readout but I cannot see it while driving down the road because it is bolted under the rear seat. My radar detector, however, has a digital voltage reading that is very accurate (verified against HP Tuners voltage reading and a standalone volt meter) when running off of a cigarette lighter port. As I have it "hardwired" using a mirror tap adapter, however, it reads a consistent 0.7 to 0.8v lower than actual alternator voltage, again verified numerous times with HP Tuners and with a meter. The morning I noticed the problem, my radar detector voltage showed as high as 14.3v and 14.4v for a couple minutes. As soon as that voltage fell back to under 14.2v the inverter stopped whining. So even though I do not have a direct reading at the inverter, I am quite confident in my estimate of actual voltage.

3. I grew up in an electrical minded household due to my dad's career and I abhor sloppy electrical and crappy connections. To explain my setup, I have coming directly from a free stud on the main fuse panel, a 2/0 battery cable that goes to an ANL fuse holder, which is currently fused with a 100amp fuse just because I haven't bothered to order a 50 yet. On the other side of the fuse holder exits an 8awg wire with crimped lugs that makes a short hop to the relay. This relay does not have plug in terminals for the load side, it has studs for lugs and is rated at 200 amps. 8 awg leaves the relay and travels to the hot side of the inverter. The inverter ground is also 8awg and goes directly to a stud made into the cab, I believe I chose one of the ones which holds the jack bracket.

After installation I verified that the inverter receives the same voltage as the battery at both zero and a heavy load. The 8awg wire is sufficient as it is rated higher than the internal fuses in the inverter and does not even think about getting warm under load.

The morning I encountered the issue the inverter was not loaded at all. It was switched on via the relay but it was not actively being used. The problem started when the voltage crept up to a certain point and stopped immediately when the voltage fell. It is not a flaky wiring problem, it is not load related.

My best guess is that ultimately it's a pretty cheap inverter from walmart and they just didn't put a ton of thought into the upper voltage limit and/or they expect sloppy crappy wiring with a large voltage drop. Combine that with no doubt sloppy tolerances from the Chinese components and it all stacks up to the perfect storm to cause annoyance under exactly the right set of conditions.

The best answer is probably to buy a better inverter but I figured I would investigate the free or cheap alternatives first. If the "fix" costs as much as a higher quality inverter then of course the answer is obvious.

[KYSilverado04]

Installation Pictures

inverter.jpg
wiring.jpg