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Old 08-15-2014, 10:14 AM   #1
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battery charger in addition to inverter

I'm redoing my boat's electrical and I'm wondering: since the inverter will charge the batteries, do I need to have a battery charger also? I don't quite understand how the two work together.
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Old 08-15-2014, 10:32 AM   #2
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no..but having one as a backup is nice as inverter/chargers seem to have more than their share of failures.
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Old 08-15-2014, 10:34 AM   #3
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The inverter is designed to charge the batteries it draws from. You can add an auto charging relay to also have it charge the starting batteries, or continue to use your existing charger for those. What additional batteries do you have? Genset starter? Bow Thruster? Electronics?

Stop right now, close your computer and get a copy of Nigel Calder's "Boat Owners Mechanical and Electrical Manual". The first three chapters cover your project in easy to read detail. Then you'd be better equipped to come back here and ask boat specific questions, if at that point you even have any anymore.
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Old 08-15-2014, 10:46 AM   #4
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Thank you

Appreciate the advice--I'm going to order the book now and do my homework
Kind regards.
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Old 08-15-2014, 09:06 PM   #5
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An inverter will not charge the batteries it's connected to unless it's an "inverter/charger".

An inverter/charger, as one might suspect, is an inverter and charger built into one package. If you have just an inverter (as I do), you will need a separate charger.

If you don't understand this, don't attempt to wire your boat without qualified help. If you buy a book and don't understand it, get qualified help.
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Old 08-16-2014, 12:04 PM   #6
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Thank you for additional info, Ron. And yes, I'll get professional help !
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Old 08-16-2014, 01:51 PM   #7
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If you have to ask that question you should not be doing the electrical work.

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Old 08-18-2014, 09:31 AM   #8
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no..but having one as a backup is nice as inverter/chargers seem to have more than their share of failures.

Agreed , the best seems to ne the portable units with a timer built in.

Most are 10-12a and are by far the best bet for recharging a battery that has gone DEAD, not down 56% 70% but down DEAD.

The fancy chargers need some sign of life from the batt to begin to recharge , these just need to be clipped on.

Have an interior light stay on in your car for a week?,,,
similar can happen to noisemaler , thruster or windlass batts .
Stuff happens , a stupid timed charger is one cure.

A batt drawn down to 100% will recharge but will never have its full abilities restored.
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Old 08-18-2014, 11:08 AM   #9
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Quote:
An inverter will not charge the batteries it's connected to unless it's an "inverter/charger".
Thanks for clarifying that Ron, I made a bad assumption that a newbie could well misconstrue.

Inverter/charges do not seem to have more than their fair share of problems, at least not the top tier brands. I suppose if you are using the inverter off a house bank that also supplies DC loads , having the ability to attach that bank to the starting bank's charger would make a lot of sense, why not? But we are going to start confusing things here discussing all the permutations.
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Old 08-18-2014, 10:45 PM   #10
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There is another more subtle reason to have a separate charger in addition to an inverter/charger. The voltage on many docks can be quite low, and most inverter/chargers look for some minimum threshold of power quality before they switch over. If the power is marginal or bad, it may never kick into charge mode and just keep running your AC off of the batteries. I'm experiencing this now on a dock with 208V. Even with a boosting isolation transformer, there are still times when the voltage is too low for the inverters to kick into charge mode.

A stand alone charger, on the other hand, typically has a very wide range of allowable input voltages and frequencies. The charger will start and run on pretty much anything. In these situations, and if appropriately sized, the charger can both compensate for the inverter's continued draw on the batteries, and give the batteries a charge as well.
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Old 08-19-2014, 10:12 AM   #11
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I remember a thread a long time ago on another forum where the poster wondered why his inverter/charger was not keeping the batteries charged.

Eventually, after several back and forth posts, it was determined that he thought the salesman told him that the inverter/charger would keep his batteries charged without being plugged into shorepower!

It wasn't clear if the salesman actually told him this or it was a misunderstanding but we got it cleared up for him.
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Old 08-19-2014, 12:15 PM   #12
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Another reason to have a second charger is to run both chargers when using the generator. This reduces generator run time. To have this work you may have to have a battery switch which creates for charging purposes two banks.
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Old 08-19-2014, 12:48 PM   #13
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I like having a separate charger for house vs start batteries. I have a separate battery bank for the bow thruster and a separate smaller charger there.
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Old 08-19-2014, 01:14 PM   #14
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On the Mainship I put 2-35 watt panels for the occasionally used batteries, one for the thruster and the other for th gen-set start. Both stand alone systems. No Long heavy gauge run to the 8d right next to the thruster. The gen set stand alone because if all else fails, ig you can start your genset there is hope.
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