ACR with Inverter Question

[ESGWheel]

While this is a hypothetical question the answer will impact the design I am doing. I assume others have a set up similar to this so looking to understand what they did or perhaps my thinking is all wet.

Scenario: Two House Batts., One Start Batt. all 12V lead acid type and same model, coupled with an Add A Battery ACR. Alternator max output is 85A and hooked into the Start Batt. 2000W Inverter tied into the House Bank. All wiring and fusing correct. Inverter capable of drawing 2000/12 = 165A.

Here is the question: when underway and cursing what happens when the inverter is loaded up almost to max which exceeds the Alt output and the ACR is closed?

With the ACR is closed I think the Alt will be loaded to its max and potentially burn out due to its higher voltage than the House Bank. In other words, with the ACR closed, the Alt. will attempt to provide the full inverter load until it cannot and drop its voltage under the strain until the rest is provided by the House & Start batt (Start as well since ACR closed)

And while the Alt voltage output may drop to the ACR’s Open Low of 12.75 (30 seconds) or 12.35 (10 sec.) it seems that this is still unhealthy for the Alt. And it seems this cycle will continue, ACR open, Alt. voltage goes back to normal and thus ACR closes, but voltage drops again causing ACR to open. Repeat. And based on fuse sizes, the Start Batt to ACR may blow.

Is my thinking correct? It seems so based on what I have read. So what have others done when trying to take advantage of an ACR but also have an inverter that exceeds the Alt output? Thanks for your thoughts.

 

[Chris1956]

Gee, alternators charge max all the time w/o burning out. What makes you think your's will burn out?

 

[ESGWheel]

Its my understanding that the Alts. are not designed for 100% duty cycle. Perhaps that is wrong, but i am under the impression that its about 60%.

 

[Chris1956]

OK, so if your car battery goes dead, and you jump the car to get her started. Would you not expect the alternator to charge at or near max?

Now if the alternator is shorted to ground, the diodes in the voltage regulator will likely be damaged, but not the alternator windings.

 

[ESGWheel]

OK, so if your car battery goes dead, and you jump the car to get her started. Would you not expect the alternator to charge at or near max?

Yes, for a limited period of time. The question revolves around a continuous load greater than the capacity of the Alt in the scenario outlined above. Are you saying alternators are rated for 100% duty cycle? Thanks for your continued thoughts on this.

 

[Chris1956]

Gee, I think you are asking a different question now. Running mechanical devices at 100% capacity is likely not good for any of them. i.e. Run your car at 100% of power for an hour and see what happens.

Are you really going to use 165Amps of power for an extended time? If so, you might get a genset, as your batteries will go dead pretty quickly with alternator power alone.

Drawing 165 A of power for a limited time is probably fine.

 

[ESGWheel]

Communication is hard, but yes that is what I am trying to convey in the hypothetical scenario above > that the inverter is trying to continuously pull 165A on the House batteries (which it can do to a point) but then the ACR relay closes coupling the House Bank to the Alt (via the Start Batt). What will happen? And since I assume folks have put in inverters with a greater capacity then their Alt AND have an ACR to charge up their House while underway, what do they do? Leaving the inverter off or disabling the ACR are two possibilities but it negates the purpose of having them to a large degree.

 

[Pmt133]

Chances are the inverter would trip before any serious damage would occur. I don't think voltage would be able to be maintained by the bank once the combine breaks for long enough to cycle more than once or twice before the inverter itself under voltage protects....

That being said if it didn't, ACR would open once whatever predetermined voltage is set and stay open until it combines again when voltage satisfies. And it would probably do that a couple times until you hit the low voltage lock out of the ACR. Alternator will mostly be fine for this. I highly doubt it would be hours or long enough to cause long term damage...

Personally the generator is a good idea or maybe adding a second alternator to take up some slack. Do you know what you're typically pulling off the alternator to begin with? Maybe you're already closer to max output than you think....

 

[ESGWheel]

Personally the generator is a good idea or maybe adding a second alternator to take up some slack. Do you know what you're typically pulling off the alternator to begin with? Maybe you're already closer to max output than you think....

Thanks for the input. While the Inverter will be pulling only about ½ of the Alt capacity that is not a guarantee. In other words, if the “policy” is do not turn on this or that on the AC side, it’s not a guarantee. So, I am looking to understand the limits in order to make the design as robust and fool proof as possible. Genset, 2nd Alt. not an option.

 

[Pmt133]

Thanks for the input. While the Inverter will be pulling only about ½ of the Alt capacity that is not a guarantee. In other words, if the “policy” is do not turn on this or that on the AC side, it’s not a guarantee. So, I am looking to understand the limits in order to make the design as robust and fool proof as possible. Genset, 2nd Alt. not an option.

Ignoring everything else.... Short answer, you won't hurt the alternator or anything else.

 

[ESGWheel]

Thanks but I think you are misunderstanding. I am looking to know what will happen if it’s run like as outlined in post 1 (and not at 50%).
More specifically I’m hoping someone with a similar set up can highlight what they did to avoid overloading their alt if fact it would overload the alt (which I think it will).
It’s a question about worst case and what if anything others have done to protect against it.