Ford Transit USA Forum banner

Alternator output

28687 Views 39 Replies 15 Participants Last post by  orton
Has anyone measured the actual output of the alternator voltage? I want to look at the possibility of using the alternator to provide a partial bulk charge to a lithium battery. Volts must stay below 14.5V.

Sent from my Pixel XL using Tapatalk
1 - 2 of 40 Posts
Just starting on my Transit but a couple of comments from charging lithium in a Sprinter.
Lithium batteries could easily draw 2 to 3 times the battery size in current. So a 100AH battery could safely use 200 to 300A. Clearly something that would not happen in a Transit or Sprinter. The sprinter alternator cables are only AWG 2 so as the current goes up there is more voltage loss in the wire. At high currents the voltage out of the alternator also goes down. The max I have seen, in a sprinter with a 220A alternator, was 80A. (I use 00 cable to connect to the transfer switch.)
I would expect the same from the Transit. It has a 180A alternator but would only deliver less than 100A due to voltage loss in the wire and the alternator voltage going down to protect itself.
But, when near full charge with the charge current going down the charge voltage goes up. I see 14.2V on a Sprinter. The Transit should be close since this is about the correct voltage for a standard battery. In my system (solar and alternator) I used a switch to disconnect the alternator once near full charge, to keep from overcharging the lithium. My Transit build will automate that function.
In my experience there seems to be very little gain in capacity by charging lithium (Voltronix) past 14V.
The 14.9V, mentioned earlier in this string, should / would never be applied to the battery unless there was some sort of a failure.
See less See more
  • Like
Reactions: 1
Groovy2 I think you are being a little too pessimistic.

In a previous build I used 480AH of Lithium Iron (the only type being used in RVs and much more forgiving compared to what is used in a cell phone or laptop). My standard MorningStar MPPT solar controller had a standard profile that was perfect and I used a cheap BMS circuit to disconnect the battery from the alternator when the correct voltage was reached. I used 14V.

Most of the time solar was fine to keep things charged. When I used a lot of microwave or the electric water heater the alternator would pump out about 80A to get to full charge pretty quickly. In that build (a sprinter) the factory wire to the alternator was AWG2 and there was enough voltage drop in the wire that the max current is limited to about 80A despite using AWG00 wire from the battery to the transfer relay. I suspect the same would be true of the Transit. I did not order the heavy duty alternator.

1 - 2 of 40 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.