Articles: Power

Doing things the wrong way: equalizers and converters

There are many advantages to having a 24 volt system on your boat when adding high load DC powered devices like windlasses and bow thrusters. To avoid excessive voltage drops from these high current devices in a 12 volt system requires large, heavy, and expensive cables. By switching these high load devices to a 24 volt battery bank system, cables that are a quarter of the size can be used to output the same power.

However, there are a few drawbacks to 24 volt battery systems - one of these drawbacks being that a lot of devices can only run on 12 volts.

After working on a boat for a few weeks, we noticed that there was a second 12V battery bank hidden under the forward bunk. What's more, the voltage across this battery bank was -8.4 volts! That is not a typo - this battery had gone in to reverse polarity! Further investigation was required to find out how this could be possible. \

From what we deduced from the wiring, which was a jumbled mess, several things must have happened. At some point the windlass was changed, and a dedicated 12 volt battery bank and control relays were installed in the bow area. Now this set-up can be a good idea, since the cable runs to the high amperage windlass become very short. Therefore, large gauge wires are not required as little voltage drop occurs. This dedicated battery bank sees minimal power drain because the windlass is run infrequently and so the charging cable can be relatively small as well. This second battery bank was being charged in parallel to the house bank.

 Now here is where someone got creative. At some point (we assume after the windlass), the previous owner had a 24 volt macerator installed. BUT instead of adding a 24 volt battery bank or another 24 volt source, they tried to wire both banks in series to get 24 volts. Wiring two 12 volt banks in series to get 24 volts sounds like a good idea, right? Wrong. I can imagine the ensuing confusion and sparks flying around as the installer tried to get this to work. Several wires, of what would have been a working windlass system, were cut and just left hanging.


If you remember, the windlass bank was being charged in parallel with the house bank, but now they're also wired in series, creating a dead short. So they cut the charging circuit to the forward batteries along with some of the other wires that powered the windlass. OK, now the macerator may have even worked for a while, but if you look at the circuit below. In reality, the windlass bank now connected in reverse every time the macerator was run.

This is the wrong way to wire batteries but it does happen, as we have seen. There were several ways to make this system work properly, including converting his house to 24 volts and using a 12 volt equalizer or a 12 volt converter to run his 12 volt loads. Another solution would be to install a new 24 volt battery bank in addition to his 12 volt bank.

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