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Old 04-08-2016, 07:20 AM   #21
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"I'm still not clear on what the risks are to motors or other AC gear if the voltage is too low. Do they simply shut down or does it damage them?"

Modern AC motors demand a certain number of watts to operate.

V x A = W

So a 120v motor requiring 1200w to operate will draw 10A from the source.

The same motor at 100V will tale 12A from the supply.

AS the voltage drops the amp draw goes UP , yet the wires that make up the motor do not get thicker to handle the higher amps..

After a low enough voltage ,, a better grade motor will pop an overheat sensor , or an internal circuit breaker ,

but the chance is the feared "white smoke" will come out , and the motor will need a rewind or replacement.

IF you can,, always purchase any AC motor "universal wound" meaning it will have brushes in a brush holder.

Will be marked AC/DC.

These are fantastic as feeding them low voltage does not increase the amp draw, it simply makes the motor less powerful.

These are a great yard sale find for power tools for on board work with a non sine wave inverter or small gen set with a low power factor.

Also nice at home where 250 ft of extension cord will still operate a chain saw , just a bit slower.
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Old 04-08-2016, 07:48 AM   #22
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So here is my take...... A/C units.... even the most sophisticated newer models will accept voltages between 187 and 253 VAC for a 208-230 supply.
As mentioned earlier, when the voltage goes down, more current is drawn. When you are at the bottom of that range, a brownout/surge can have detrimental effects on not only HVAC/refrigeration equipment, but also any AC electronics.

One thing to take into consideration is how often you would be in this situation. Not all owners are subjected to a lot of different voltages, and in their case, I would not recommend the Iso-boost, unless they just wanted it to help with resale value later.
OTOH if they are coastal cruisers visiting many different marinas, I would recommend it.

There are ways to connect your isolation transformer to allow variable "taps". This is a more cost effective approach. That is if the isolation transformer has multiple taps for voltage adjustment. This setup would mean you would check the incoming voltage, set the tap to the proper incoming by a rotary switch prior to turning power on. IMHO this is as good an option as any.

Just my $.02
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Old 04-09-2016, 06:40 AM   #23
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It is a shame that the isolation transformer folks do not add to their product line.

With little effort the unit could function as a great power supply.

Take DC from the alt , chop it up and reassemble as "house current" for any application'\

With a DC noisemaker the unit would work as well as the new Honda gas units ,
no fixed operating RPM, just enough to supply the load.

And of course they could operate as a boost inverter does , taking juice from the batts to help a rotten dock power source or a tiny noisemaker get that 2nd or 3rd air cond started.
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Old 04-09-2016, 09:26 AM   #24
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If you are going to be spending a lot of time on a 208v dock with AC running, I'd advise doing something. Some sort of voltage booster will pay for itself over time in longer equipment life and usability of the boat. Find out if the isotransformer you getting a deal on can be tapped for switched boost. The manufacturer can tell you this and likely give instructions how. Or spring for the boost add on from Charles or Ward's (would be worth giving the latter a call and getting their advice).
I believe Charles sells a 50 amp Isoboost isolation transformer.
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Old 04-09-2016, 09:49 AM   #25
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I believe Charles sells a 50 amp Isoboost isolation transformer.
Yes, I had two of them on my Hatteras. They also sell boost-only for those who already have an isolation transformer and can't, or don't want to, hassle with tapping and switching. Wards makes one too and sells all.
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Old 04-09-2016, 02:35 PM   #26
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Originally Posted by seadogmike View Post
So here is my take...... A/C units.... even the most sophisticated newer models will accept voltages between 187 and 253 VAC for a 208-230 supply.
As mentioned earlier, when the voltage goes down, more current is drawn. When you are at the bottom of that range, a brownout/surge can have detrimental effects on not only HVAC/refrigeration equipment, but also any AC electronics.

There are ways to connect your isolation transformer to allow variable "taps". This is a more cost effective approach. That is if the isolation transformer has multiple taps for voltage adjustment. This setup would mean you would check the incoming voltage, set the tap to the proper incoming by a rotary switch prior to turning power on. IMHO this is as good an option as any.

Just my $.02
Thanks, Michael. Sounds like it's rolling the dice to assume shore power will be adequate and not damage equipment unless I have a boosting transformer.

Unfortunately, the unit that sounded like such a good deal doesn't allow variable taps. So I'm thinking I'll bide my time and ponder this some more.

I have also seen ACME buck and boost transformers advertised as "marine" units that are priced appealingly, but they don't mention ABYC compliance.
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