Originally Posted by r3meyer
What are you using to protect your alternator? Most can’t take the charging of Lipo and burn up.
… well this question came up faster than I thought.
When I first researched this I knew that our Alpine can handle 8 house batteries and I thought that it has a monster alternator able to supply 250A+... come to find out the standard unit has 160A.
So lets explain for a sec why lithium batteries burn up alternators:
The charge current of a lithium battery is defined as a C rating i.e. my 400Ah battery at 1C (that is common) can take 400A with no problem. There are charge currents possible up to 5C … albeit not recommended by the manufacturer.
So a Lithium battery charges quicker that is one of its prized advantages and it does so because of its lower internal resistance (compared to lead acid).So the current flow is high and our little alternator would be running pegged out until the battery protect opens the circuit for high voltage. I would think at that time you can sweep up the melted aluminum housing from the alternator somewhere.
There are many van conversions out there i.e. the Sprinter running Lithium with no problem and a smaller alternator but that is because the current is throttled by the temperature of the alternator … ours is not.
So here are the solutions that I found:
#1 Just have the chassis battery connected disconnect the lithium from the battery isolator and be happy … hey maybe the sun is shining while you are driving.
#2 If money is no object I would install a DC to DC buck Boost. it limits the amps to what you programmed and even better it can take 12V from the alternator and still charge a 24V system if you would ever change to 24V down the road. Now that is nice... and expensive.
#3 just like the modern alternator we can throttle the current by using the sense wire and a temp probe on the alternator. The Balmar MC614H will do exactly that … not a bad solution as it will certainly provide longevity to our alternator no matter what.
#4 and this is the solution that I favor at the moment is to install a Victron 12/1200 and a fuse that limits the current. This is really nifty so the installed fuse lets say 50A will heat up once its gets to tis designed current limit and thus changing its resistance the controller can sense that and throttle back the current. The nice part is that you can install a fuse as you see fit for the possible current. With our 160 A alternator I think charging with 50A while driving is plenty … maybe 80A I have to see.
So there you have it. I took my coach for a 1h ride measuring current and temperature without anything in place right now and all was very much in spec but I ordered the Victron 12/1200 yesterday as an add on.
Also if you think about it once the battery isolator connects both batteries all the current will flow to the lithium battery and very little to the chassis battery … path of leased resistance. So this is another reason to add the current limiter.
Looks like I have to learn how to write shorter posts