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Old 21-01-2016, 12:27   #1
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DC over voltage

Hello, first-time poster here.

I have an RV that had an old battery charger. Based on opinions I found here and elsewhere, I decided to replace it with a ProNautic 1230. That's why I'm here, this forum seems like a better resource than anything dry land-specific. The install went fine, and everything is working great from what I can tell.

EXCEPT: When it's charging now, with temperature compensation on, I see the voltage getting up to 15.2V, as it should. But the way I have it wired, the house appliances are seeing this same voltage. The furnace in particular is blowing really really hard, and I know this isn't good for it (It's speced to run up to 13.6V).

It seems like this should be a common problem, yet I haven't seen any solution in all the research I've done. No diagram I've dug up of RV or boat wiring seems to address this. Do others just let the house appliances run on higher voltages?

It looks like I might be able to solve the problem with a DC/DC converter like this:

8-40V to 12V, Step-up + Step-down, 120W : Current Logic, Expert of DC-DC Converter

Says it takes in from 8-40V and outputs 12V. I think 120 watts would be enough for my modest needs.

But I am curious what others may have done.

Thanks!
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Old 21-01-2016, 16:15   #2
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Re: DC over voltage

I'd ask here:

Marine Battery Chargers - Installation Tips & Considerations | SailboatOwners.com Forums scroll to the top.

The charging voltage appears/sounds to be way too high. Where did you get 15.2 from?
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Old 21-01-2016, 16:21   #3
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DC over voltage

Sounds like maybe it's in equalization?
I don't see over 15 V being normal in any temp?
I know nothing about that charger though

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Old 21-01-2016, 16:31   #4
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Re: DC over voltage

I concur, that sounds like equalization.

When our batteries are cold, the regulator allows the voltage to climb as high as 14.8 but never higher.


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Old 21-01-2016, 16:54   #5
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Re: DC over voltage

What kind are your batteries? Highest normal charge voltage I've seen is 14.8 for flooded lead acid. My charger is set to 15.5 for equalization only and there is a warning to turn off voltage sensitive equipment before equalizing.
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Old 21-01-2016, 16:57   #6
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Re: DC over voltage

The battery is flooded. It's the temperature compensation, it is programmed to start at 14.8 and I'm usually charging in temperatures below freezing. I can't find the spec for how the ProNautic does it, but here's something you can read if you want:

http://www.tekrispower.com/pdfs/xant...20Charging.pdf

Regardless, even 14.8 is outside the operating limits of the furnace and lights, so back to the original question?
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Old 21-01-2016, 19:39   #7
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Re: DC over voltage

Say 14.7 is the battery manufacturer recommended absorption voltage. This is at 77F/25c. If the batteries are 32f/0c , the absorption voltage should be raised to 15.3v.

Temperature compensation and all. All battery manufacturers will post details how much to raise or lower absorption and float voltage based on temperature, with absV at 77F being the figure most people quote as being correct for ANY temperature.

When one is plugged in, unless there is only a limited time to remain plug in, one could just charge slower at a lower voltage. It will take longer to reach 100%, which might not be a factor, but a healthy battery should still be able to eventually reach a full charge at lesser voltages.

The absorption phase should be about 4 hours long, so one might decide to just turn off the furnace while the charger is in ABS mode and turn it back on when the charger reverts to float.

I think if the speed of the furnace at 15.2v was distressing to me, I'd put a PWM motor speed controller on it, rather than putting a voltage bucker on the circuit.

http://www.amazon.com/VicTec-Motor-S...SF6J3N40CW0V9A
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Old 21-01-2016, 20:16   #8
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Re: DC over voltage

Quote:
Originally Posted by Sternwake View Post
Say 14.7 is the battery manufacturer recommended absorption voltage. This is at 77F/25c. If the batteries are 32f/0c , the absorption voltage should be raised to 15.3v.
Makes sense to me.....Our batteries never get below about 50f
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Old 21-01-2016, 20:23   #9
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Re: DC over voltage

Yeah, it's the temperature compensation, I'm in a cold place. Thanks Sailmonkey.

The speed of the motor seems a little distressing, but there's also a logic board in there I don't want to fry. Plus all the lights and maybe the fridge... What do you see as the downside of using a voltage bucker?
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