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From: Scott H.E. Welch (no email)
Date: Wed Mar 01 2006 - 13:05:57 EST
Steven Dubnoff <> writes:
>The question was about "equally", and the specs for the Vanmar
>"equalizers" advertise a range between .1 volts and .5 volts at full
>load. Now, half a volt is a very big difference in battery
>voltage. A converter, in contrast, draws from the 24 volt supply and
>guarantees that the batteries have the same voltage at any
>load. That is a good thing.
True. But on the other hand this is in a loaded condition, whereas most of
the time the loads will be minimal and the voltage will be very accurately
even (I know because I have digital meters on both banks).
>
>A well built equalizer is a switching power supply with 99%
>efficiency. It will deliver solid, well regulated 13.6 volts from
>any reasonable input voltage.
True. But...
>Plus, if the $500 prices quoted on
>equalizers are to be believed, you can buy two 30 amp converters for
>the same price.
Also true, but....
>Put one in the pilothouse and another in the engine
>room. Run thin 24 volt wiring to the converter and less fat 12 volt
>wiring to your 12 volt electronics --- save money and copper all around.
Also true, but....
>
>However, I run my entire boat on one 30 amp converter. Raytheon
>electronics do not care about their input voltage. It is only vhf's
>and a few other odd things that require 12 volts.
>
>I may be dense, but I cannot see a good argument for choosing an
>"equalizer" over a battery converter.
Well, there are a number of arguments I could make.
First, by using a converter you now have a single point of failure for all of
your 12 volt electronics. That right there is pretty bad. With the equalizer,
even in the case of total failure you can continue to draw a 12 volt load,
since the load is being supplied by the battery, not the equalizer.
The next thing is sort of related to the first, and that is that you can draw
much higher loads. For example, I am going to add a few small 12 volt winches
on my boat. These draw about 80 amps, which I can do no problem, even with a
50 amp equalizer. Why? Because the equalizer is effectively a *charger*. not
a supply. I can draw a few hundred amps of 12 volts for short periods, and
the equalizer will quickly use the 24 volt bank to charge the 12 volt bank.
The final thing is that switch-mode power supplies are not totally benign.
They are electrically noisy, they generate heat, and they do not always
generate pure DC. All of those problems are eliminated using an equalizer.
So, all in all, I think that the equalizer is the way to go.
By the way, just as an aside, I also kept as many of my loads as possible
(all lighting, SSB, windlass, starting, etc.) 24 volt in order to minimize 12
volt drain.
One final note, there is one downside of using an equalizer, and that is that
it is impossible to use a amp-hour based battery monitoring system.
Scott Welch
FirstClass Product Manager
www.firstclass.com
"The person who makes no mistakes usually doesn't make anything"
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