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Old 04-13-2019, 12:57 PM   #12
bglad
Senior Member
 
City: Green Cove Springs, Florida
Join Date: Feb 2012
Posts: 344
Series parallel explanation

Taken a few minutes to put this together. Let me know if it makes sense:

The thruster battery bank should not back feed 24-volts to your other system. The only place that will see 24-volts is the output of the series/parallel switch. You can prove this by monitoring the voltage where the current charging leads attach while running the thruster. You will only see 12-volts. However, if the charging leads positive is on one battery and the negative on other then a short circuit will occur which you should be able to remedy.

I have attached a diagram that explains this. The series parallel switch has the batteries in parallel when at rest and in series when making 24-volts. If you look at the circuit you will see only the positive and negative of one battery should be connected to the engine starter (charging source) when the system is in parallel.

Properly connected the only thing that may happen is the batteries will go slightly out of balance since only one of the pair will be charging as the thruster is in use if wired the same as the diagram. This should resolve itself in short order once the thruster is put back to rest.

Quote:
Originally Posted by Wil View Post
I want to wire my 200a (continuous-rated) alternator directly (with a fuse of course) to my 12v 900Ah House bank, then automate the charging connection to my 12v/24v 220Ah Start bank. Both banks have the same charging profile.

The unusual issue is that the Start bank (2xG31) is normally in 12v (parallel) configuration, but will go into 24v (series) configuration via a heavy contactor when the bow thruster is 'Activated' by a manual switch in the wheelhouse. After the thruster is de-activated, the Start bank goes back (contactor relaxes) to its normal 12v configuration for charging, engine & generator start, and windlass use.

The way the boat builder (KK) afaik dealt with the voltage disparity/bank separation issue is to have an Alternator Output Selector Switch (AOSS) manually switched between either the House or Start banks, or Both banks combined. So the boat operator MUST remember to never activate the bow thruster when the two banks are combined. Also don't try to start the engine or generator, or run the windlass when the bow thruster is activated. This system has potential for fireworks , so I want to improve it.

The attached drawing shows three possibilities. All are meant to go where the boxes with question marks are in the drawing. I'm using 4/0 in that line for an emergency engine start if Start bank was critically discharged.

Regarding possibility #2, I have an inquiry into Sterling-Power-USA whether the PSR252 https://www.sterling-power-usa.com/P...solator-6.aspx will withstand the Start bank in 24v configuration trying to backfeed to the 12v House bank. If it can, that seems simplest and most reliable way to do this. And it doesn't have the inefficiency/voltage drop issues of regular battery isolators.

The Blue Sea ACR (will close when charging voltage at House bank is present) and RBS (will open when bow thruster is activated) seem a bit busy (less reliable?), and the heavy diode & DC to DC charger (to deal with diode voltage drop) seem lossy and clumsy.

This is a situation I haven't dealt with before, so any constructive advice or out of the box thinking would be most appreciated.
Attached Files
File Type: pdf Thruster series parallel switch diagram.pdf (89.2 KB, 48 views)
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