High output alternator charging a high capacity carbon agm battery bank

Abdul

New member
Hello

Please excuse my English as it’s not my first language.

I have a land cruiser 79 series single cab. It has a 1gr-fe engine the same engine in the Fj cruiser from 07-09. My truck is used for my daily commute and overlanding. my first setup was a 100 amp hour lead acid cranking battery and some other accessories connected to it like my ham radio, led light bar and tire air compressor the things I use mostly when the engine is running. A second 100 amp hour agm battery connected to the first battery via an isolator. I use it mainly for my chargers, camping lights, a small dometic 12v fridge freezer and a 3000W inverter which I use daily to cook my lunch in the instant pot as I drive home from work (the distance is 100 miles) I usually have the instant pot running for the first half of the drive then stop to have lunch. This setup lasted for a year. After that I have noticed that my charging system cannot keep up with my needs. When the engine is idling the volts go down to about 10.5v while the instant pot runs. So I started my research I have found out that my stock alternator is JUST 80amps!!! and 13.2v when hot. I started looking for a replacement I have found a local shop that could fit a large Mercedes 180amp alternator in place of the stock one by doing some custom bracket. On my first overlanding trip I was in the middle of a desert without any cellphone coverage and the nearest town was 20 miles away the custom bracket broke so I lost everything my charging system, my power steering and my cooling system luckily I had my satellite phone with me so I called a friend and he came and he towed my truck. I wasn’t comfortable doing this again. So I started looking around again and I found an old guy who has designed a custom bracket to fit a 140 amp GM alternator as a second alternator he was doing this for more than 10 years without any problems so I went to him and installed it. I was very comfortable going this way because if god forbid something happen I have my stock belt and I can just install it and my truck would be still running.11853595-544F-43B8-B183-19AAA57E971D.jpeg 92006536-A075-4518-A227-CA7074438219.jpegThis is my stock alternator down there.
70786C9D-B20B-4EE3-8F7E-591E04C4CC1F.jpeg756FD064-1E46-48BD-96EB-31E4C0CAC963.jpegAnd this is the GM alternator. This is the part number
B9659313-5184-4AEF-B5B6-735F76032DBB.jpeg

I’m planning on adding camper in my trucks bed. I live in a hot climate we average a 47 degrees celsius in the summer ( 115 degrees fahrenheit) so air conditioning is a necessity. I’m going to buy a small 5000BTU air conditioner I found a unit that draws 500 to 600 watts. I’m going also to fit 4-217 amp hour agm lead carbon batteries Northstar Blue+ and the second alternator would be responsible for just charging these four batteries directly. Now my stock alternator is making some whining noises it has to be replaced. My plan is to buy a mechman alternator they have one that replaces my stock one and it’s 240 amp it will be used for charging the two batteries inside the hood with my old isolator and I’m going to buy another 400 amp alternator also from mechman that will replace the GM unit and it will be used just to charge the batteries in my camper (the 868 amp hour batteries). Is my plan good? Is the 400 amp alternator going to harm my battery bank from the high voltage? Will the 400 amp alternator fit? Because as you can see the GM alternator is sandwiched between the engine and the second battery. Is there a DC-DC charger that supports +200amps?

Thank you for your time11853595-544F-43B8-B183-19AAA57E971D.jpeg
 
Last edited:
Do you have a DC-DC charger in between the starting battery and house batteries, in addition to your isolator? I see that a full size Instant Pot is rated at 1200 watts. I wonder if the the charging system can keep up with the draw while cooking?
 

Abdul

New member
Do you have a DC-DC charger in between the starting battery and house batteries, in addition to your isolator? I see that a full size Instant Pot is rated at 1200 watts. I wonder if the the charging system can keep up with the draw while cooking?


Thank you for replying.

Now the isolator is connected to a switch inside the cab just incase I needed to jump start from my auxiliary battery.
The instant pot I have is 1000w when the engine is idling the volts drop down to 12.0v-12.4v But when I’m cruising the volts are stable at 13.7v.
Each alternator is connected to its battery directly without any DC-DC chargers.
 

Abdul

New member
My only guess is that the inverter is drawing too much from your electrical system. What gauge wires are you using ?

I’m using 2 gauge from the second alternator to the auxiliary battery (Less than 2 feet) and 2 gauge from the auxiliary battery to the inverter (Less than 3 feet)
 

Forum statistics

Threads
185,538
Messages
2,875,656
Members
224,922
Latest member
Randy Towles
Top