alternator and mppt

[native pepper]

as long as he runs it through the MPPT - AND the MPPT is set for LiPoFe voltages - should be no problem.
Not knowing the type of alternator? could be an issue running at full output if the MPPT can use it (60a?)

Don't know the brand, they are old, second hand from a wreckers. Don't actually put out 60 amps, one puts out around 52 amps and the other a bit more he said. They are set to charge to 14v and theory is, unlike going straight into a battery and the building up resistance slows the charge rate, as in lead acid. hopefully, going through an mppt, there would be no resistance and the alternator would keep putting in full amps until the voltage hit 14v in the lifepo4. The mppt would switch off charge, the alternator wold stop producing because of the resistance in the wiring from the charge going nowhere. The cells would settle to 13,8 until they dropped to the restart voltage and a full charge would be put in, not a trickle.

If it works ok will probably put a couple of 120amp on the kubota, may even attach it to the trailer and run it on veggie oil. Nothing like having a few hundred amps available for a quick recharge of the bus if we ever get stuck without sun for a week or more, could even charge others rigs if they ran a bit low.

Told him, he should tap the ac side of the alternators and get a direct ac voltage, which I believe can be obtained by regulating the speed of the alternators. Like me, it drew a blank with him, saw my mate do it a few times when experimenting with cheap ac generation. My understanding which may be wrong, is if you bypass the alternator regulators by tapping the ac side of it, you can control the voltage output. You probably need some form of ac regulation, but don't have a clue what that would be.

Dibs, he only just got his cells, not sure of the exact price, wasn't involved this time, but think it was between 60 and 53cents an amp for the 50amp cells plus freight etc. When I got mine, paid 72.5c an amp, plus freight and customs charges for 45amp cells. Bus ones cost me 64c an amp for 40amp ones and got my 12amp portable 40amp and some spare cells from free.

[bagmaker]

he may have to keep an eye on the alternator temperature, full output for long periods, old age, etc..

[native pepper]

Spoke to him yesterday, he's got it all set up and only using one alternator to test it. Doesn't want to blow 2 mppt's up. so will tread cautiously and says it will only run for a hr or two, pumping in over 100amps. He has his panels so this is a backup and as he has been using lead acid for decades to power his house, has yet to experience or understand the huge difference in usability he will have. So reckon, like my lister, it will sit for very long periods of time doing nothing and my kubota may never get setup, my 700amh on the house has been adequate since got them.

[T1 Terry]

Where does the alternator output go when the MPPT controller deems the battery to be fully charged? Where does the alternator sense battery voltage? A separate voltage sensing wire or internally?
The simple and easiest method is the connect the alternator to the battery via the battery monitor so all charging current is recorded. If it has a separate voltage sensing wire, connect a voltage boosting circuit to a DPDT relay with the common connected to the alternator sense wires, the N/C to battery and the N/O to the voltage booster circuit set to 14.8v. Simply power the relay when the battery has reached the target voltage, this will send 14.8v to the alternator voltage sense wire and internal voltage regulator will stop the charging until it sees less than 14v again.

The house system I'm just finishing off has 600Ah @ 24v, equal to 1200Ah @ 12v, the house uses 54% over night but even in over cast showery conditions the 5.6kW of solar still cover the day time house use and get the battery back to 97% by sun down.
Today is a sunny day and at 10am the system was putting 92amps @ 27.5v across the battery after powering the house needs and there was 80Ah remaining to bring the battery back to 100% SOC....... what to do with the remaining 6 hrs of solar input that peaks for 3 hrs at 130amps?
Bought a cheap and turned out to be nasty 4000w modified sinewave inverter to dump excess into the 3600w hotwater element, the smoke came out as soon as it was powered up even with nothing connected..... now have to wait for the evil bay seller to either send another one or buy a better quality unit and fight for a refund....... but that will only use up an hr or so of excess output, then what do we do with the rest? Is this what they call a 1st world problem

T1 Terry

[native pepper]

Where does the energy go when you try charging a dead battery and it doesn't take the charge, doesn't the alternator protect itself from battery malfunctions. Doesn't an alternator requires an energy source to produce energy, so when the mppt cuts out, there would be no power to incite the alternator and it would stop producing.

That's our logic, which could be entirely wrong. He should have it up and running now, so will drop in when get the chance and see how it all went. It''s a really simple setup, the only difference is where the charge went straight to the batteries, it now goes to the mppt.

[T1 Terry]

The average automotive alternator has an inbuilt voltage regulator, older models had internal voltage sensing while newer models have a voltage sensing lead and a warning light wire that requires power to get the alternator charging. An alternator produces AC voltage and uses diode to rectify this to DC voltage. There is a voltage drop across any and all diodes and this creates heat so serious cooling is required in a high output alternator running at full output for an extended time.
Once the alternator starts charging it will produce its max possible output in regards to speed and temp till the voltage regulator senses the target voltage is reached, then it reduces the current on the field windings which in turn reduces the output.
If the alternator is putting out its max output and it suddenly has no where to go, the voltage climbs very rapidly. With and internal voltage sensing model the voltage regulator will react and lower the field current and the output current will reduce till the target voltage is met, but this takes a while so a voltage spike is created, then the output voltage reduces and the current tries to flow back to the lower voltage side of the output diodes......not good for extended diode life and will often cause an instant failure of at least 1 diode in the diode pack and generally a cascade effect until the whole lot fails.
It is even worse with an external voltage sensing type that has a voltage sensing wire, it only sees battery voltage and not the fact something in between has blocked the output current. The voltage spike is huge and generally the alternator goes up in smoke.

I can't see any advantage in putting an MPPT controller between the alternator and battery, what would you gain?

T1 Terry

[Wilbor]

I can't see any advantage in putting an MPPT controller between the alternator and battery, what would you gain?

T1 Terry

That is what I suggested, connect direct to the LiFePo4 and keep a close eye on the voltage. My understanding of this setup is that the Diesel engine running an alternator was for emergency use only and that solar was the main power source

[native pepper]

I can't see any advantage in putting an MPPT controller between the alternator and battery, what would you gain?

T1 Terry

Full and proper control over your pack, no need to switch anything other than from panels to kuboto and just the same charge controller and equaliser.

Saw him last night, he has been worried that as we've had a few days of very little sun, his pack would run to low before it could be charged again and we are looking at the same again this week. That's why he wanted to get the kubota connected, because that's how his AGM batteries acted and he was expecting the same, or similar.

But he soon discovered that lifepo4 charge really fast and his 1000ah pack switched off in the morning after just a couple of hours of sun and was full on the first day. So he hasn't fired up the kuboto and is so happy that he has heaps of energy, amazing what 10kw of solar will do for a lifepo4 pack, compared to agm over just a couple of hours. His lady is extremely happy, she has been able to do anything she wants, without worrying whether there will be enough power for the night. She now wants induction cook tops like us, bigger TV, another computer for the kids and electrical kitchen aids.

Expect he will fire up the kubota one day and will let everyone know what happens.