New user

Re: New user

More small controllers tend to cost more than one large controller.

The small Morning Star has a maximum of ~70-75 VDC input, the larger ones have ~150 to 600 volt maximum input voltage (depending on model).

The fact that the controllers are not "coordinated" (end bulk, enter float) at exactly the same time) is not going to cause much in the way of problems. More or less, it just bugs the owner that the charging phases are not in synchronization.

The engineering issues with multiple parallel devices (whether controllers, battery strings, etc.)... Is that, typically, the more devices you have, the less reliable the system.

Yes, you do have redundancy (N+1 redundancy is a very common engineering solution for reliability). But, on the other hand, you have to design it to both have the ability to detect masked failures (a battery bank with 4+ parallel strings of batteries and a single open cell or cable connection is virtually undetectable in normal operation with standard hardware). So--If you have a "simple" N+1 installation and hidden failures, the system quickly become non-redundant.

Also, you have to protect against failures in redundant systems that you would not normally have if the system was not redundant. If you have a parallel battery bank and a shorted cell in a battery--That shorted cell will start drawing current from the rest of the parallel strings--Which can cause the rest of the bank to "go dead" unexpectedly, or even start a fire in the shorted cell/battery string (shorted cell overheating, or over charging other cells in the string).

And then there are the maintenance issues--If flooded cell batteries, each string is just that many more cells to check SG in and water.

As Marc mentions--Paralleled hardware/batteries need more fuses/breakers/wiring. More costs and chances for failures. If you don't do the design correctly, a short circuit can become that much more dangerous. If you have ever had a battery bank short of some sort (glowing red hot cables, all hard bolted to battery terminals and no switch/fusible link)--You would know the helpless of trying to find a large pair of cutters, fire ax or something to try and stop the current--Or just stand by and hope that a cable eventually burns out.

None of us are trying predict that bad things will happen to your system. We are just using good design guidelines to reduce the chances of failures and provide a reasonably safe system. Reasonable can be different for different people/installations. If the battery system is in a metal shed 20 feet from the home--Perhaps you can just let a (rare but possible) fire/short burn itself out. If the system is built in the middle of your home/cabin and a fire will take out the cabin and put your family in danger--Then different design guidelines may be a good idea.

We try to paper design systems that will not only work well 1-2 years in, but will still meet the operational requirements 7-10-20 year in the future.

Nobody here is looking to argue or slag somebody's system. However, if asked and we see safety or possible long term design issues--We will comment. We try to error on the side of safety and reliability--But the owner that will take suggestions here with a grain of salt. Hopefully we are helpful--But we do try to be educational.

-Bill