question

dr-bob avatar image
dr-bob asked

Cyrix CT giving too low a voltage for charging

I have had a new narrowboat delivered with a Cyrix CT linking the engine start battery to the bow thruster battery. When the engine is started, the alternator is delivering 14.4V (as normal) but the voltage on the two battery terminals of the Cyrix are typically 13.8V to 13.9V and the two batteries the same voltage (although the bow thruster is down around 0.1V - long wire run to front of boat). In the two weeks we have been off-line only once did the voltage reach 14.0V. Voltage is reported on the Victron BMV712 smart and also checked on my calibrated multimeter. Voltage recorded via my Rasp Pi running the victron software.

Anyone got ideas why the Cyrix is dropping the voltage (or is anything else likely to be dropping it)?

Cyrix Battery Combiner
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2 Answers
ceriw avatar image
ceriw answered ·

The Cyrix switching element is just a relay so there is almost no voltage drop across it - as confirmed by your measurements of the terminals. Sounds like the voltage is being dropped elsewhere before the Cyrix - wiring or connectors maybee?

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dr-bob answered ·

Thanks Ceri. That is what I had assumed - it is just a relay.

I have checked all the connectors I can see - but it is new boat so not sure of where all the wire runs are. The battery leads to the 87 and 30 terminals are 50mm cables so likely to be direct to both batteries but a fuse on one side. I'm not even sure where the fuse is to check the terminals on that.

I guess if the alternator is showing 14.4V and the 87 and 30 terminals 13.8V then any bad connection is going to be between the alternator and the 87 terminal. Is that correct?


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