Report of First BD with Lithium/Solar

[lsbrodsky]

Here was my thinking: I really do not know how the BMS works, in terms of multi-staging. I do know that it balances cells and stops charging when the battery voltage requires same.
The best move would have been for me to wire to portable panel through the Victron solar controller, along with the roof panels. But, I took the easy path by using a simple 7-way adaptor, easy to plug in to the trailer cable. That cable charges just like the alternator.
When I watched voltages and charging current at both the solar controller and the battery, I could see that these two were not fighting each other. When charging was required and enabled, I was getting plenty of charge from both. I cannot say whether they fight in absorption or float, but they do not seem to in bulk mode. Works for me.
Larry

[uncle_bob]

Hi

Proper BMS operation with a lithium setup (yes if you spend enough money they
integrate the BMS into a stack for you...).

1) The device monitors the cell voltages in the stack. To get to 12V you need multiple cells. If one gets in trouble you very much want to know about it.

2 The device (may) equalizes the charge on the cells. When cells are manufactured, there is a tolerance on the capacity of the cells. One of the "tricks of the trade" making stacks is to sort the cells into groups and use similar capacity cells to make a stack. If you buy cells individually ... not so much. If you buy from some guy named Bob who doesn't know how to match them .... not so much. Even with matching, the charge on the cells will not be dead equal. You can only do so much. The equalizing circuits take care of the imbalance.

Why do these things matter on Lithium? The reason you *want* lithium is that the output voltage holds up very well as you discharge them. The flip side is that unlike lead acid, the output voltage does not self equalize over quite as wide a range. Large capacity cells need help in this area. How much help? When you see the super duper "5,000 charge cycles" numbers up in the bold print, they are talking about an equalizer setup (or a single cell). When you see the posts about "my Lithium's only made it to 800 cycles", that's a stack that could have used some help.

Yes, there is the *possibility* of something really nasty happening. Put a lead acid charger on a Lithium stack and you are asking for trouble. Put a dead short across one (no fuse ) and things will get really warm really fast. Have a cell in a stack go dead short (without detection) and you likely will loose the rest of the cells. None of this is very common. If it was my trailer, even an uncommon risk fire engulfing the whole thing would be something to avoid. Even more so if it was relatively cheap to do.

Bob

[lsbrodsky]

Bob,

Not sure what your message is. With an all Victron setup, everything is taken care of. The batteries are top notch, the BMS is intended for the batteries, and the I/C is setup for Lithiums. The latest batteries have individual cell monitoring, but mine pre-date that. The trucks alternator and the portable solar feed, instead of the alternator, are the only voltage sources not coming through a Victron controller and they feed the BMS, which takes care of shutting them off when required.
Larry

[uncle_bob]

Originally Posted by lsbrodsky

Bob,

Not sure what your message is. With an all Victron setup, everything is taken care of. The batteries are top notch, the BMS is intended for the batteries, and the I/C is setup for Lithiums. The latest batteries have individual cell monitoring, but mine pre-date that. The trucks alternator and the portable solar feed, instead of the alternator, are the only voltage sources not coming through a Victron controller and they feed the BMS, which takes care of shutting them off when required.
Larry

Hi

In your previous post you stated "I don't know how the BMS works" ...now you know.

Bob