Empathy List Archives

trawlers@lists.trawlering.com

TRAWLERS & TRAWLERING LIST

Re: T&T: 12/24Volt wiring ???

Steven Dubnoff

Wed, Mar 1, 2006 5:08 AM

However on the particular subject of drawing a 12 volt load from a 24 volt
battery bank, contrary to other posts there is in fact a way to do exactly
this.

Since I was the "other poster," I should probably respond to this
message. The exchange was

Does anyone know if there is a way to connect a 12V load "equally"
to two batterys in a 24V series system?

My response was:

There isn't and it is generally a bad idea. A much better idea is a
24 to 12 volt converter.

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.

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. Plus, if the $500 prices quoted on
equalizers are to be believed, you can buy two 30 amp converters for
the same price. 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.

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.

Best,

Steve

PS For a good thread on this subject in rec.boats.electronics, see:

     http://makeashorterlink.com/?K4A0619BC

Steve Dubnoff
1966 Willard Pilothouse
www.mvnereid.com
sdubnoff@circlesys.com

>However on the particular subject of drawing a 12 volt load from a 24 volt >battery bank, contrary to other posts there is in fact a way to do exactly >this. Since I was the "other poster," I should probably respond to this message. The exchange was >Does anyone know if there is a way to connect a 12V load "equally" >to two batterys in a 24V series system? My response was: There isn't and it is generally a bad idea. A much better idea is a 24 to 12 volt converter. >>> 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. 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. Plus, if the $500 prices quoted on equalizers are to be believed, you can buy two 30 amp converters for the same price. 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. 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. Best, Steve PS For a good thread on this subject in rec.boats.electronics, see: http://makeashorterlink.com/?K4A0619BC Steve Dubnoff 1966 Willard Pilothouse www.mvnereid.com sdubnoff@circlesys.com

Scott H.E. Welch

Wed, Mar 1, 2006 6:05 PM

Steven Dubnoff sdubnoff@circlesys.com writes:

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"

Steven Dubnoff <sdubnoff@circlesys.com> 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"