Bud Martin
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Victron video: How to not blow up your Alternator when charging Lithium.
Victron: How to not blow up your Alternator when charging Lithium
- Thread starter Bud Martin
- Start date
Notice with the lithium battery alternator the rpm is higher than the stock alternator.
The theory is good but the test should have the same rpm and therefore cooling on both alternators.
Plenty of people let their engine idle with a high load on the alternator (bad).
It does show that manufacturers should have temperature derating of alternators from factory.
The theory is good but the test should have the same rpm and therefore cooling on both alternators.
Plenty of people let their engine idle with a high load on the alternator (bad).
It does show that manufacturers should have temperature derating of alternators from factory.
Alphacarina
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Unless you're driving a steady speed down the freeway, plenty of low speed operation is eventually going to occur - That's why the used of a DC to DC charger is so highly recommended
Don
I understand (sorta) about lithium charging profiles. I have a B2B. The question I have is; is it okay to run my alternator directly to the lithiums for short periods of time. Not talking unsupervised, long drives, or routinely. Say 1/2 an hour.
mikefitz
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Provided there is a reasonable amount of resistance in the feed to the lithium battery to keep the current at acceptable levels and you are able to monitor the process, I would think there would be no issues.
I have tested such an emergency arrangement in my RV and sail boat in case of B to B charger failure.
In a vehicle at engine idle speed, I would think pulling around 25% of the alternators rating would be safe, as much of the vehicles loads would be off, ( wipers, heater motor, headlights).
In my tests using around 4 meters (12 feet) cable run with series fusing and 16mm2 cable (AWG 5) at 50% battery capacity, the current was 38 amps. Alternator rated at 160 amps, output 14.3 volts at engine speed 700rpm, battery 220Ah.
As part of the experiment I found adding link fuses in the cable run gave a volt drop up to 100mv per fuse and thus reduced charge current.
Mike
"Provided there is a reasonable amount of resistance in the feed to the lithium battery to keep the current at acceptable levels". Can you tell me what that means please. Not to charge the batteries to 100%? Or is it not to charge them from 0%? I haven't gotten around to understanding the internal resistance thing if that's what's at issue.
mikefitz
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The issue was discussed in depth here.
Experiences charging LFP from alternator WITHOUT a DC-DC charger
Does anyone have medium or long term experience charging a LFP house bank from the alternator without a DC-DC (B2B) charger. Either using an external regulator, a purpose built alternator, or just cavalierly ignoring safe methods and hoping for the best. Whatever the case I would like to hear...
diysolarforum.com
In simple terms regard the current into the battery being controlled by the resistance in the charging circuit,
Amps = (alternator voltage - battery voltage)/ circuit resistance4
Mike
That really didn't clear things up for me very much. I'm getting the impression that internal resistance goes down with the soc. So charging directly from the alternator is less likely to cause problems for either the alternator or the batteries with partially charged batteries. I'm thinking to test this out with the soc between 50 - 80% with me right there watching the monitor and shutting it down once I come to some feeling as to what will actually happen. Specifically interested to see the how the volts and amps compare to what comes through my B2B.
SoC doesn't change IR significantly enough to remove this problem. They'll still happily take as many amps as the alternator can throw at them (cable resistance notwithstanding).
So an alternator puts out xxx amps. And a portion of that goes to run the vehicle. And what's left over should be available to the storage batteries. And that the amps an alternator produces varies with the condition of the alternator. Am I understanding this approximately correctly? The question I'd like to find an answer to is; is there a way to measure how many amps are being used for basic vehicle functions and what is the maximum total the 'my' alternator will generate?
Zwy
Solar Wizard
This must be the 10,000th post about charging LFP with an alternator. It's getting old, use the Search function and read up on it.
You will find the LFP bank will take whatever the alternator can produce for amps. You run an alternator at full load for extended time frames and the rectifier will overheat and burn out. Alternators put out max output under high rpm, lower rpm produces less and also leads to lower cooling.
How to determine vehicle base load? Simple, inductive clamp placed around a battery cable at idle, all accessories on including blower motor on high, ac on, all lights on. Then inductive clamp is placed at alternator lead and see if the 2 match. Record both, then look up alternator capacity in a parts catalog for your vehicle. Some vehicles have options for higher output, take for example a mid 2000's Chevrolet Silverado, some had the 130a alternator and some had an optional 165a. If you can't determine which one, then go with the lower amperage one. Subtract your recorded readings from the alternator rated output, divide result by a factor or 2 and that would give you an approximate amperage you could utilize for charging auxiliary batteries. Alternators never were designed to be battery chargers, they are designed to maintain a battery and supply electrical loads of the vehicle.
You will find that if you continually overload the alternator, it will burn out. It's that simple. Idle is the worst time for an alternator as the temps underhood can get high, the fan in the alternator will not move as much air and alternator output is low due to low rpm. Loads are constant so this taxes the alternator quite heavily.
Use a DC to DC charger to limit load, your alternator will thank you for it.
It depends on what your alternator is rated for. Without that rating we're just guessing.
According to specs the alternator is 136A. I've been reading some things on StackExchange that suggest, (suggests - not says) that it doesn't take a lot of juice to run the basic functions of a car. Maybe 2A for the ignition. 2 for the fuel pump. My vehicle in question is a 2000 so it doesn't have a lot of the modern car dependance on electricity. Fan runs off the belt and etc. If I'm not running a heater, aircon or some such high draw device it sounds to me like there should be lots of left over juice. Wife's away with it not but I will be testing when she gets back.
So the wife is back. I tested the draw to the chassis battery = 14A+-. It's about what expected. This is sitting in the driveway with nothing in particular drawing power beyond the normal day to day systems and the battery voltage at 14.6. The draw to my lithiums, either directly from the alternator or via the B2B was 34+-A. The lithiums were at 25% soc. So the B2B will I suppose control the voltage and over time the amps but I can't see much harm in 'short term' charging of lithium directly from an alternator. Beyond that issue, and more importantly, what this adventure tells me is that if my alternator is up to spec and capable of producing 135A it shouldn't have a problem charging my lithiums through the B2B. All of these readings were done with the vehicle idling and the ambient around 60F. I'm given to understand that the real problem with using an alternator to charge house batteries is over heating so I'm still left with that question. Hot hot should it get and how to measure it. Appreciate any input.
