Getting power from a 12 v high (250amp) alternator into my lithium bank

[Benihanas]

ok guys so I want to know how I can get a ton of power into my battery bank using a high amp alternator (or even how fast it would be safe for the batteries to charge).... planning on having 9kw of lithium from bigbattery, not sure if im going to do a 24 or a 48 v system yet (leaning towards 24 but I might do a 48)but I know Ill need the power... im going to have two 370 w seraphim panels on the roof (12' wide body box truck converted to an overland vehicle) to help keep me topped up during the day but I will also be running an air conditioner that draws about 600 w of power almost every night, so it would be awesome to charge up a nice chunk of the 9000w really quick during my daily one or two hours of driving and allow the panels to keep me topped up from there.. I looked into the Sterling bat to bat charger but it looks like its limited to about 800W per hour of charging and a 70 amp input, which completely shuts down the idea of using a beefier alternator... is this possible? would I be able to use an isolator and rely on my batteries BMS? im completely clueless about this particular part and would love some clever opinions.

thanks in advance, been here for a few days and already learned so much couldn't be more appreciative!!!

 

[Benihanas]

anyone?

 

[sshibly]

Op,
I will have a DC to DC charging solution for my 280AH Eve pack someday.

Things to consider:

1. Do you know the output curve of your alternator?
Do you think you have access to all 250A at 13 volts at your disposal at all times?
Are you going to be charging when you are parked?
If you are parked, will you sit in the driver's seat and plant your right foot on the gas to keep the engine RPMs at 2500 rpm?

Take a look at my Ford Transit's Alternator curve:

FORD Transit BEMM - 2016.5

Ford Transit BEMM. Has details of alternator ouput, wiring etc. Too Big to upload here. Page 131 has the output curve for Ford's factory HD alternator with temp. This is good guide to understand Alternator's output curve.

diysolarforum.com

I plan on charging my batts when I get back on the interstate and drive at around 2000 RPM, I am guessing from my HD unit curve, I will get around 150A.
I plan in using NO MORE than 60A of this to charge battery.

If you are going for a 48v system, then that means you will have 15A @ 48v, this number might make you want to cry like a 2 year old, well join the club.
FYI: I have a high idle ECU option, but my 3.5 twin turbo gasser with direct injection might run into trouble in carbon and other curd.

A 2k honda genset and an electrical charge looks very attractive to zaaaaaap mucho amps into your 48v battery.

 

[jwelter99]

Sterling Power for a B2B. Call them as they have some newer models that are higher power about to be released but delayed due to COVID.

They will have options up to 3500W output. The 12V to 12V will be 240A output at lithium compatible charge voltages.

 

[mikefitz]

Adding an additional 24/48 volt alternator is one option, and is the better method of extracting power from the engine.

Extra Large Case Alternators - Balmar

Extra-Large Frame AlternatorsDesigned for Heavy Duty Cycle Applications 97EHD-Series Designed for Extended Duty Operation Case Ground or Isolated Ground Terminations Available Maximum RPM: 7,000 External Regulation Required USCG Title 33 Compliant Extra-Large Case 97EHD-Series Alternators are...

balmar.net

With the existing alternator the most you could expect with reliability is around 100/150 amps at idle speed, thats 1200/1800 watts with a 12v alternator. Any battery to battery charger 12 to 24/48 will not be 100% efficient, say 1000/1500 watts output to the battery pack.

You could use a combining relay with a direct connection to the alternator/starter battery and rely on the system resistance to limit the charging current into a 12v lithium battery.
With suitable cables and equipment its possible to have a 12v system running air con and appliances, its not the most efficient but works and is common in European RVs.

Mike

 

[jwelter99]

Adding an additional 24/48 volt alternator is one option, and is the better method of extracting power from the engine.

Extra Large Case Alternators - Balmar

Extra-Large Frame AlternatorsDesigned for Heavy Duty Cycle Applications 97EHD-Series Designed for Extended Duty Operation Case Ground or Isolated Ground Terminations Available Maximum RPM: 7,000 External Regulation Required USCG Title 33 Compliant Extra-Large Case 97EHD-Series Alternators are...

balmar.net

With the existing alternator the most you could expect with reliability is around 100/150 amps at idle speed, thats 1200/1800 watts with a 12v alternator. Any battery to battery charger 12 to 24/48 will not be 100% efficient, say 1000/1500 watts output to the battery pack.

You could use a combining relay with a direct connection to the alternator/starter battery and rely on the system resistance to limit the charging current into a 12v lithium battery.
With suitable cables and equipment its possible to have a 12v system running air con and appliances, its not the most efficient but works and is common in European RVs.

Mike

Also worth pointing out most new Transits and E450's have the option of twin 12V alternators that get you just under 400A total. If you have such a platform it makes sense to try to utilize this. In my case I have a twin alternator E450 so wanting a 12V input B2B that could consume 200 - 250A was the best path forward to use the alternators that came factor installed and factory warranted.

With the next-gen Transit slated to get the hybrid option out of the F150 this will open even more options for van builders as the inverter, battery, generator, and in motion charge is all handled for you. Question will be how easy it is to add solar/shore charging.

But fully agree that going from 12V to 24V or 48V will never be as efficient as using the correct voltage alternator. I do still prefer a B2B and not just a combiner (as you point out with Balmar the B2B is replaced with the smart regulator they offer) to adjust for charge voltage based on RPM/Temp/Battery chemistry. And Balmar is really the top choice here.