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If ok to use MPPT solar controller as a DC to DC connect to Car alternator to charge LifePo4?

gingerboy

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Aug 13, 2020
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Hi, think about this idea for a while. Use the Car alternator directly charge the LifePo4 is a NO GO, damage the battery and burn out the alternator.
But how about put in MPPT controller on it?
I have a spare MPPT controller, it has function limit charge current. If I set the charge current like 20A, 25A, will it be safe?
 
Unlikely the alternator can provide sufficiently high voltage for the MPPT to operate.
 
Adding to what snoobler said above, my Victron MPPT requires the input voltage to be +5 volt higher than the battery voltage to start charging. Once charging has started, the input voltage only needs to be +1 volt higher than battery voltage.

So no, your solution probably won't work.
 
My car is 2009 Lexus RX350, just check it start the car with battery voltage 12.2V. Checked voltage from the alternator cable, (not the battery terminal), it read from 14.56 to 13.85, I believe it depend on the battery SOC. Going to try it when I have time.
 
Adding to what snoobler said above, my Victron MPPT requires the input voltage to be +5 volt higher than the battery voltage to start charging. Once charging has started, the input voltage only needs to be +1 volt higher than battery voltage.

So no, your solution probably won't work.
yep, think about the cheap boost converter, but those are all charge range from 24v - 72v, not 10 - 15v to 14V.
Reason I am thinking about it, to charge the LifePo4, absorb can be just 14.0 - 14.4, and float just 13.4 - 13.6. It seems to be fit.
 
Forget it, there are $10-$20 boost converter module on eBay, just set the output voltage to 13.4, much easier to setup and wiring.

Thanks.
 
If you are trying to protect the alternator, why would anyone want to be using the MPPT's current boosting feature?

I thought the purpose of using an MPPT was to use the charging current limiting. Set the MPPT charging Volts to 13.3 - 13.5 and stay away from the upper knee.
 
Since you have a spare, give it a go. Love to hear the report.

BTW have you checked the manual?
 
If you are trying to protect the alternator, why would anyone want to be using the MPPT's current boosting feature?

I thought the purpose of using an MPPT was to use the charging current limiting. Set the MPPT charging Volts to 13.3 - 13.5 and stay away from the upper knee.

What is a "current boosting feature?"

MPPT has a POWER boosting feature, where max power is extracted at optimal voltage and current.

MPPT is a DC-DC converter, much like the DC-DC chargers. It has a maximum output. If the concept were viable, a 20A MPPT would only put out 20A to the battery and pull a little less than that from the alternator.

If you could get an alternator to output 16V+, it would probably work on most MPPT.
 
What is a "current boosting feature?"

MPPT has a POWER boosting feature, where max power is extracted at optimal voltage and current.

MPPT is a DC-DC converter, much like the DC-DC chargers. It has a maximum output. If the concept were viable, a 20A MPPT would only put out 20A to the battery and pull a little less than that from the alternator.

If you could get an alternator to output 16V+, it would probably work on most MPPT.
My understanding is that Volts in excess of the charging Volts are converted into current. So, current is boosted.

My Morningstar SSMPPT 15L has a 15A current limit, although a lower current can be set. I run 400W with 9.5A ISC of solar which could generate 30A.
I think what gelmjw meant was that an MPPT device can see 36v but only 8 amps from the PV and turn that into ~12v @20amps (for example) to the battery.
That is correct.

My SCC could be used to limit a charge current to 15A or less to the battery. The SCC would see a 100A, 14V output from an alternator as a 1400W power source. However due to the 15A limit, no more than about 200Watts would be drawn from the alternator. The output current is settable from 0 to 15 Amps.
 
yep, think about the cheap boost converter, but those are all charge range from 24v - 72v, not 10 - 15v to 14V.
Reason I am thinking about it, to charge the LifePo4, absorb can be just 14.0 - 14.4, and float just 13.4 - 13.6. It seems to be fit.
Yeah those boost converters might do the trick. Clever idea, let us know how it goes. Hopefully it's safe.
 
My understanding is that Volts in excess of the charging Volts are converted into current. So, current is boosted.
Boost controllers actually raise the voltage, often used for eBikes and other high voltage devices. Basically the opposite of a normal MPPT.
 
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