How to not blow up your Alternator when charging Lithium - Victron Energy

Korishan

Korishan

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Typical alternators in an engine are not setup 1:1 gearing from the engine so the presentation is a bit misleading for the result at 1500 rpm. The LiPo at 50% SoC terminal voltage would also be around 11.5V, way below the normal float of 13.2V for a car battery and even lower than the 14.2V desulphate. Pull any generators terminal voltage down well below what it is designed for by attaching an inappropriate load and it will fail.

Guess it's also a great advert for the incompatibility of "12V" lithium working voltage range, compared to lead-acid. Big blue door stops ?
 
OffGridInTheCity said:
Its a great reminder that details matter. Its what makes the discussions on this forum so interesting.
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Interesting. So the moral of the story is to properly size your car battery to the alternator.

They used a 3.6kwh battery at 50% SoC. That's rather large. A car battery only needs to have a high cranking amps, not high capacity. A lithium battery should always be at 80-100% SoC (unless you left the car unused for over 2 years) and if properly sized it should have been charged and should reach absorbtion charging stage relatively quickly and the current draw would have been reduced dramatically.

I can see people in using converted vans into RVs using a separate battery as their power source and would use the car engine to charge the main battery instead of an external source such as solar. In this case I can see why a properly sized alternator is needed and with regulation. I think this is more inline with what Victron is trying to explain, rather than a blanket Lithium ion is bad for alternators.
 
not2bme said:
Interesting. So the moral of the story is to properly size your car battery to the alternator.
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I would say it's best to size your alt to your battery. In these types of cases, the battery is built to handle a certain type of load beyond what the vehicle was originally designed with or could handle, and/or for use while the engine is turned off. Then charging is done when the engine is started when leaving/moving/etc.

not2bme said:
They used a 3.6kwh battery at 50% SoC. That's rather large. A car battery only needs to have a high cranking amps, not high capacity. A lithium battery should always be at 80-100% SoC (unless you left the car unused for over 2 years) and if properly sized it should have been charged and should reach absorbtion charging stage relatively quickly and the current draw would have been reduced dramatically.
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They used a 50% SoC battery strickly to draw the most amps possible as they wanted to demonstrate the possible/max loads that would be stressing the alt. I agree that normally the battery would only be 70-80% SoC as the lowest.

In the video they demonstrated what would happen if the alt ran at lower rpms. This is what caused the issue. And note, it wasn't the heavy load that destroyed the alt, but the lack of air flow keeping the alt cool.

This is the biggest problem using a standard alt to charge Lithiums, or any battery really. As he stated, an alt is only about 50% efficient, due to the heat produced. The reason there is heat is because the alt is self energizing. There are no magnets. If you were to take out the field coils and replace them with neodymium magnets, the efficiency would drastically improve. However, I'm sure there's more to it than that to do a conversion.
 
Korishan said:
I would say it's best to size your alt to your battery. In these types of cases, the battery is built to handle a certain type of load beyond what the vehicle was originally designed with or could handle, and/or for use while the engine is turned off. Then charging is done when the engine is started when leaving/moving/etc.

They used a 50% SoC battery strickly to draw the most amps possible as they wanted to demonstrate the possible/max loads that would be stressing the alt. I agree that normally the battery would only be 70-80% SoC as the lowest.

In the video they demonstrated what would happen if the alt ran at lower rpms. This is what caused the issue. And note, it wasn't the heavy load that destroyed the alt, but the lack of air flow keeping the alt cool.

This is the biggest problem using a standard alt to charge Lithiums, or any battery really. As he stated, an alt is only about 50% efficient, due to the heat produced. The reason there is heat is because the alt is self energizing. There are no magnets. If you were to take out the field coils and replace them with neodymium magnets, the efficiency would drastically improve. However, I'm sure there's more to it than that to do a conversion.
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Exactly my point, it's not a lithium issue. It never was a lithium issue. It was just a matter of sizing either the alternator or battery. They used an oversized battery for what the duty cycle of the alternator was made for. It was made for charging a car battery under normal operations.
 
Well, that may be so, but they were also proving a point. ;) A standard alt without taking into considerations/factors will blow your alt up.

And yeah, I agree it wasn't a lithium issue. There's a reason why those people who make those vehicles have the sound system of a rock concert tucked in their trunk use multiple alts. Some of the crazy designs they go through to make it all work is just plain ridiculous
 
Korishan said:
And yeah, I agree it wasn't a lithium issue.
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At one point, it sounded like they were saying that Lead Acid has such a high IR ... the Lead Acid could *not* accept (and soalternator does not produce) as many amps as the Lithium-Ion with lower IR / can accept more amps.

It seems like a large Lead Acid battery bank would also 'overdraw' on an alternator - since multiple Lead Acids in parallel could 'accept more amps' - same as Lithium-Ion in the test.

Does their statement about a regular car battery not being able to accept very many amps so alternator will not overheat at idle make sense?
 
OffGridInTheCity said:
At one point, it sounded like they were saying that Lead Acid has such a high IR ... the Lead Acid could *not* accept (and soalternator does not produce) as many amps as the Lithium-Ion with lower IR / can accept more amps.

It seems like a large Lead Acid battery bank would also 'overdraw' on an alternator - since multiple Lead Acids in parallel could 'accept more amps' - same as Lithium-Ion in the test.

Does their statement about a regular car battery not being able to accept very many amps so alternator will not overheat at idle make sense?
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Oh yeah, that's right. The LA's have a much higher IR so charge current naturally regulated by the single/double batteries.

An alt has an internal regulator. It detects how many amps are required and will output what is needed (not sure of how it detects this). But also, the alt's amp output is proportional to the speed at which it turns. When the engine is at idle, the alts max amp output is only a fraction of what it's rated for. That's why when you have a dead battery and get a jump, you rev the engine to about 2000rpms to help charge the dead battery, and then after the jump, you drive to charge the dead one. Don't just idle.
 
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