How to not blow up your Alternator when charging Lithium

In this video, we put both a traditional and a regulated alternator through its paces. Using different RPM's, we charge a 300ah lithium battery and test the results.

[philippschneidenbach]

Ok, so the actual perception is: 3000 alternator rpm if created from a 1000rpm engine with general overdrive of ratio 3 gives healthy 40ish degrees and 78.9 Amps off of a 70a Citroen Alternator. Good.
Real verdict of this video without the voice is that a fully loaded alternator should not be operated below 1000 engine rpm (=do not 100% load in idle, which is not hard to understand) but is very fine when driving (lets say approx. 2000 engine rpm).
Regarding Lithium everybody should know that a lead acid battery as a buffer to avoid load off voltages and then DCDC off to a Lithium with current limiting to a current value/number below (80%) the alternator limit is a good ballpark.

[Goodkiwibloke]

In an internal combustion engine situation, the alternator typically runs at 3 times crank speed. So 1500 crankshaft rpm = 4500 alternator rpm = way out of danger zone.

Your test rig seemed to run alternator rpm = motor rpm = overheat problem

[fourfortyroadrunner]

Your comment about the 1500RPM test "the engine running at idle" is incorrect. Typical engine crank to alternator ratios vary from at least 2:1, more typically 3:1 to 4:1. I have not documented modern stuff very much, it is possible that some engines are a higher ratio yet. In my day, my 440 Plymouth was 4:1, meaning, that if the engine was spinning 6K RPM, the alternator was screaming at 24, 000 RPM. I did fail a couple of them.

[freakyflow]

One of many first things i done was swapped my 85amp alternator to a 145amp alternator that was for the same make of Van with Power/heated seats option And at idle (650Rpm) it is rated to 100amps. Other upgrades was thicker copper wire And extra ground points I run a total of 400amps Life4po And 400 watt solar panel And a shore power 115volt outlet And a few Victron products to keep it all together running smooth ...4 years now And no issues

[fowler]

This is spot on for sailing boat install. I am converting to LiFePO4 batteries and was wondering about alternator charge from a small 8HP Yamaha outboard engine. So in a small sailing boat you'll have a "large" Li batterie (150-200 Ah) and a small <10 H.P. outboard engine that will not run for a long time typically. (If there is no wind I usually don't go out sailing) From your video I conclude it will make no sense to try recharge a large Li battery under these conditions and would probably don't even bother cabling it. I'll have a proper AC charger that is plugged to the AC unit in the boat when on shore, and use it to recharge the batterie.

[geraudcoste]

As many I guess, this video worried me a bit thinking I'll blow my 2 x 115A 18 year old alternators mounted on 2 Volvo Penta D4 engines. But then I kept on looking because I didn't like the more complex DC/DC chargers known to be heat producers with quite small amp output. And I found some very interresting stuff about this video such as the fact the test was made with a Citroen alternator. So I ended up thinking, what the heck, if my alternators blow, it'll just be time to change them anyway. I did the test with the following setup: 2 alternators feeding 2 Victron Argofet battery isolators with 3 outputs feeding my 3 battery banks: 1 bowthruster/winch Optima 5.5 battery - 2 port engine 5.5 Optima battery - 3 starboard engine & house battery (this one is a mix of 75Ah Optima 5.5 + 400 Ah LiFePO4). I've monitored carefully the current draw (meter + Victron App) and I've never seen more than a 120 Ah draw, even with the lithium fully discharged. I also checked the heat on the alternators and everything was normal. Actually, most of the time the charging curent is around 80Ah which should be ok for 2 x 115A alternators. This is my first year with this setup and so far it works like a charme. No anomaly seen and the Daly BMS as well as the Victron App have never reported any error. I will follow up this comment if a noticeable problem arises of course.
Geraud in the Med area of France

[LawpickingLocksmith]

Knowing the internal resistance of both the alternator and the battery is key to planing the setup. If the battery has a lower impedance, a buckboost combo can protect both. Best of all is an on dash selector where the operator can choose to limit to 80% of the capacity. Careful usage planning ahead of time will give you optimum longevity. Best to use 2 batteries for ultimate redundancy. For cold weather use a battery heating will lift life expectancy.

[gaidin]

2 things: 1, you did not simulate the engine compartment of the vehicle which typically has a radiator fan located very close to the alternator and blows air on the alternator helping with cooling. 2, as far as sudden shut down of the lithium charging which could damage the alternator, most vehicle engine scenarios include a lead acid battery in the charging loop which will absorb the output of the alternator when the lithium suddenly stops accepting a charge because the BMS shuts down charging.

[quuark]

Smart external regulators, like the ElectroMaax Pro-X, or Balmar, allow you to control the alternator output at various rpm’s, and they also monitor current flow and temperature to optimize charging and protect the alternator. ElectroMaax also has alternators with separated rectifiers to minimize heat generation in the alternator.

[MyGoogleYoutube]

"Charging lithium batteries at low RPM (revolutions per minute) can cause the alternator to overheat, potentially leading to internal coil damage." For the 1500 RPM test "....note this is still above the typical speed of an engine running idle" This indicates a fundamentally flawed understanding of how alternators are driven in vehicles by these folks in the video.

The alternator in this video was underdriven WAY below what it was designed for - no wonder it fried. Most alternators are going 3X (3:1) the speed of the engine RPM. What is the average engine idle speed? 800 RPM? Making the lowest alternator RPM of around 2400? The video shows an alternator running at 1500 rpm - so a 500 RPM engine idle?

Why wasn't the Balmar tested at a super low RPM? I am sure Balmar wouldn't have been happy with you smoking one of their alternators when it was tested outside of it's design capabilities?

I don't understand the comment about BMSs disconnecting the batteries when fully charged? Fully charged is 3.65V per cell - and by then it's constant voltage and current is just trickling into the batteries at that point. How would this harm the alternator if a load of a 50W or less was suddenly disconnected?

I charged a 200ah LFP house bank for several years using a standard Victron Cyrix combiner with zero issues. I would see around 70a going to the house batteries. I would only use this when needed and recognized I couldn't full top the batteries so I stopped charging around 90% SOC. I also monitor the alternator's output. When I upgraded to 600ah I did have go with a DC to DC because without I was getting 120A to the house batteries with a 160A alternator at idle. I went with Sterling's new DC to DCs which I think is much better than what Victron is offering currently with their Orions and Buck Boosts.

If you don't want to dive into the weeds on how this stuff works and don't want to actively control your house battery alternator charging like I am - get the Orion, get the Buck Boost, or some other DC to DC.

[andrewcheshire]

I'm gonna design and build my own. Nobody seems to have the simple idea of a dump load.

[keesras]

It is a pity you barely mention the issue of Li BMS shutting off the battery while charging. This will destroy the dynamo much faster than the overheating. How is the victron system coping with the BMS shut off?

[skinnerMTB]

DC DC is the way to go. You know it, I know it, we all know it :) Especially when you are increasing the aH. I'm upgrading my diesel pusher from 450ah flooded to 920ah LifePO4. It would have been so easy to replace my BIM-225 with a Li BIM-225, but the idea of stressing the alternator with such a high load forced my hand. So I'm losing my AUX start function, but my alternator will have a long healthy life!

[timandres]

Yeah but you are direct driving that alternator. Typically vehicle alternators are overdriven at least 3:1. Im not arguing against DC/DC converters, but your abusing that alternator to no end. The testing here is not realistic.

[bobjarrard]

I know that voice well. Hope you and the dog are well. Bob in Nevada

[keysersmoze]

Alternators are typically run faster than your tests.

[robertschulke]

What about protecting the alternator from voltage spikes resulting from BMS shutdowns, or heavy loads disconnecting?

[Nāmarūpa]

Takeaways for me personally: 1/ I need to track alternator temperature and 2/ I need to drive the field current (FR) appropriately, probably following charge state (BLK, ABS, FLT, OFF)

[antontsau]

the biggest problem with alternator is that it sits in motor so ambient temp there 100C easy.

And, yes, your alternators are typical light duty from small cars (70-90a), not designed for prolonged full current.

[TimeSurfer]

It might be a bit more complex, but what I'm thinking here is a bit convoluted and a tad expensive. The solution I see is a DC to DC Solution that I doubt anyone has addressed:
Use the Alternator to charge a Lead Acid Battery. Use the Lead Acid Battery to power an Inverter that powers a proper LiFePO4 Charger.
Alternators, after all, were designed SPECIFICALLY to charge Lead Acid Batteries.
Let them do their jobs.