I’ve recently overhauled the battery compartment on my sailboat. During the process I added a dedicated “Start” battery and a Cyrix-Ct combiner and a SmartShunt.
I’m getting a parasitic drain of the Start battery when the boat is shut down and both the “Start” and “House” switched are “Off.” In a couple of days away from the boat I’m finding the that Start battery has dropped from 12.7+ Volts to <12.0 Volts.
Recently I’ve been disconnecting the positive (+) cable that runs from Start battery to the Cyrix when I’m away from the boat. Doing so has stopped the parasitic drain. Does anyone have any thoughts on what may be causing the draw on the battery?
Look at the datasheet. The Cyrix is a relay, when it is energised (closed) it has a current draw of 220mA for the 120A version and 320mA for the 230A version. That is either 5Ah or 8Ah per day, so easy to draw down a small starter battery.
The datasheet also clearly states that if one of the batteries has a low voltage, the relay will close, so by isolating the house battery but leaving it connected you are making it energise.
This is the problem with relay based battery combiners. To stop this move the positive wire to the Cyrix to the output side of the isolation switch so when you isolate the starter battery, you also completely turn off the Cyrix.
Thanks very much for your feedback, I appreciate it. I certainly didn’t realize that the draw was so significant.
I’ll make the change you’ve suggested and report back.
It should not close:
In order to prevent unexpected operation during installation or when one battery has been disconnected, the Cyrix-ct 12/24 will not close if the voltage on one of the two battery connections is lower than 2 V (12 V battery) or 4 V (24 V battery).
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@chrigu mskes a good point, one I had missed, which makes it slightly less easy to understand it staying enegised unless there is a way for some voltage to bypass the switch. I still suggest it is wired to the off side of the switch.
So, the question becomes: Which is “Battery 1” and which is “Battery 2”?
The Cyrix schematic has terminal 87 listed as battery 1 and terminal 30 as battery 2. At present, I have the start battery as battery 1 and house as battery 2.
My house bank is huge compared to my actual needs (510 Ah, 2 x 8D), it came with the boat. The start battery is a group 34, 55 Ah cranking battery.
Should I move the house bank to the battery 1 terminal and the start to battery 2?
Afaik that doesnt matter, the Cyrix has voltage sensing on both sides, it can and will also switch if either side rises in voltage.
Ive got mine between starter and aux battery. Solar MPPT is hooked up to the starter battery, while the mains charger is hooked up to the aux battery. It will keep both batteries charged no matter which side the charge source is connected to.
This is based off the assumption that you are using a common negative on both battery banks, and are switching the positives with the cutoff switches