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Old 08-09-2010, 03:36 PM   #1
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What voltage range for the 12 volt system?

I am finally getting around to hooking back up my electrical system on my 1973 31' Sovereign International. I have a new Xantrex panel and integrated charger that I am really happy with so far. What I have noticed though is that the voltage level on the main 12 volt line that is hooked to the battery and the charger output does have variation. Of course a battery will discharge somewhat with use too when not hooked up to shore power. I have also been experimenting with getting the factory original LPG powered DC generator working. It is rated to put out voltage in the range of 12 to 15 volts. I got it running over this last weekend and was surprised to see that it was putting out voltage in the range of 16 to about 18.25 volts when direct wired to my nearly fully charged battery. The question about why the generator is putting out so much extra voltage is perhaps a separate issue. My questions about the 12 volt system are the following:

1.) What is the range that I should expect to see on my 12 volt main line? Surely light fixtures, the refrigerator and other 12 volt items would have some maximum and minimum acceptable voltage levels for their operation.

2.) Is there typically anything built into a modern charger such as my Xantrex XADC 60A charger that does anything to regulate the voltage level?

3.) Are there voltage regulator products available that can be attached to the main 12 volt line to help stabilize the voltage level there?

4.) What prevents a battery from overcharging in a typical 12 volt system? Is there something built into the charger that automatically reduces the current as the battery comes up to full charge?

5.) What would prevent the battery from overcharging if I run my propane powered generator too long?

Thanks,

Malcolm
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Old 08-09-2010, 03:52 PM   #2
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The newer converters are generally 3 stage, high charge, maintain, and storage.

With this type of converter you don't have to worry about voltage regulation.

Now if you are not connected to shore power the batteries will drop depending on your usage. While everything will continue to work at lower voltages you don't want to battery to drop below 10 volts as damage will start to occur in the battery itself.

Any 12 volt system that can not accept low voltage, computer driven items, will shut themselves down at around 9.5 volts. The control on the frig may fall into this category but the lights and radio will still work so you have to be aware as to how low the voltage is to protect the battery.
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Old 08-09-2010, 03:55 PM   #3
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That is a rough & tumble generator meant to get a battery up to 85 or 90% charged - no fancy finishing circuit on it, no taper or float regulation. You the operator are considered the computer-controlled charging logic...

Over charging would be bad only if you boiled the battery dry - exposed plates to air, otherwise the occasional mild overcharging could be considered
equalizing'. When it comes down to knowing what the battery state-of-charge (SOC) using an electrolyte specific-gravity float tester would be your best bet,

What was the battery SOC when you began? The battery holds voltages down while there is current flowing - you might've checked the voltage but did you check the current? If the battery is nearing 100% full charge current flow drops to nearly nothing and voltage will climb.

Example - a small wind turbines output will see a discharged battery as a near short circuit and slow way down, even maybe stop turning in the wind - and will see a fully charged battery as an open circuit and run away into overspeed since nothing is holding it back - its the everything inbetween that works well...

What were the connecting primary charging cable lengths and sizes? Was it as short of run as possible using the heaviest gauge wire? If too-small cable and/or old oxidized connections were in circuit than the resistance may have been high enough to keep real current from flowing and allowing the unit to show a 'open-circuit' voltage...
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Old 08-09-2010, 04:00 PM   #4
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Originally Posted by malconium View Post
1.) What is the range that I should expect to see on my 12 volt main line? Surely light fixtures, the refrigerator and other 12 volt items would have some maximum and minimum acceptable voltage levels for their operation.
You should expect to see anywhere from 12.0 to 14.5 volts.

Quote:
2.) Is there typically anything built into a modern charger such as my Xantrex XADC 60A charger that does anything to regulate the voltage level?
Yes. It has both a current and a voltage limit. I don't know about the XADC, but some Xantrex converters are temperature compensated, so that they will produce a somewhat higher voltage at lower battery temperatures.

Quote:
3.) Are there voltage regulator products available that can be attached to the main 12 volt line to help stabilize the voltage level there?
None commercially available that I'm aware of, designed for that application. It's usually not a problem. Incandescent lights are most sensitive and will still work acceptably well at common voltages. Electronics, including electronic ballasts for fluorescent tubes, generally have their own regulating power supplies to deal with slight voltage swings.

Quote:
4.) What prevents a battery from overcharging in a typical 12 volt system? Is there something built into the charger that automatically reduces the current as the battery comes up to full charge?
Yes, exactly. Older systems that predate the availability of solid-state voltage regulators designed the charger so that the current would more or less taper off at higher voltages. Many still work this way. As long as the battery is vented and kept watered and the charging current is reasonable, it doesn't matter much.

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5.) What would prevent the battery from overcharging if I run my propane powered generator too long?
Perhaps nothing, so don't do that. I'll reply on the other thread in greater detail.
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Old 08-09-2010, 06:48 PM   #5
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Quote:
Originally Posted by Wabbiteer View Post
That is a rough & tumble generator meant to get a battery up to 85 or 90% charged - no fancy finishing circuit on it, no taper or float regulation. You the operator are considered the computer-controlled charging logic...

Over charging would be bad only if you boiled the battery dry - exposed plates to air, otherwise the occasional mild overcharging could be considered
equalizing'. When it comes down to knowing what the battery state-of-charge (SOC) using an electrolyte specific-gravity float tester would be your best bet,

What was the battery SOC when you began? The battery holds voltages down while there is current flowing - you might've checked the voltage but did you check the current? If the battery is nearing 100% full charge current flow drops to nearly nothing and voltage will climb.

Example - a small wind turbines output will see a discharged battery as a near short circuit and slow way down, even maybe stop turning in the wind - and will see a fully charged battery as an open circuit and run away into overspeed since nothing is holding it back - its the everything inbetween that works well...

What were the connecting primary charging cable lengths and sizes? Was it as short of run as possible using the heaviest gauge wire? If too-small cable and/or old oxidized connections were in circuit than the resistance may have been high enough to keep real current from flowing and allowing the unit to show a 'open-circuit' voltage...
My battery is an Optima closed cell type so I can not use a specific gravity tester. The SOC was nearly fully charged when I first hooked it up but I did crank the generator over several times before the engine started up. I imagine it was purging the air out of the propane line for one thing. I see what you mean by your wind turbine example but I wonder if I will still get up to 18 volts on my main DC line at some point if I am charging the battery and it gets near full charge. I just read in the newly acquired service manual that there is a governor on the generator. Could it be that this would slow down the charge rate as the voltage comes up? The charging cable lengths were the same exact size as in normal use but the lengths were shorter. In actual fact it was part of the original charging wire that I cut off when I wired up my new main panel. The new panel was a little closer to where the wire bundle came out of the wall. The connections at both ends were fresh connections. I think the wires might be about 30" long.

Since my generator has a remote start panel with a timer that means that the generator turns off when the timer gets back to 0. I could envision the possibility of adding a simple circuit that would cut off the timer early when the battery reaches a specific voltage. Do you know of any simple pre-built voltage sensors that I could use for that sort of thing without having to build one from scratch?

Thanks,

Malcolm
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Old 08-09-2010, 08:44 PM   #6
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Danger Will Robinson!

That charger is expressly made for flooded lead-acid batteries - preferably non-automotive style deep cycles with heavy plates..

It'll damage sealed lead-acid, AGM, gel batteries since it depends on having a dumb battery to soak up its noisy dumb output. (think Uni-Volt)

It still might be usable if you feed the output into a DC to DC charger that will limit voltage and let current vary ie: large inrush on discharged battery that rapid tapers off without letting voltage climb.

Remember batteries in the 1960s were expendable especially on top-of-the-line RVs.
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Old 08-11-2010, 02:03 PM   #7
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Danger Will Robinson!

That charger is expressly made for flooded lead-acid batteries - preferably non-automotive style deep cycles with heavy plates..

It'll damage sealed lead-acid, AGM, gel batteries since it depends on having a dumb battery to soak up its noisy dumb output. (think Uni-Volt)

It still might be usable if you feed the output into a DC to DC charger that will limit voltage and let current vary ie: large inrush on discharged battery that rapid tapers off without letting voltage climb.

Remember batteries in the 1960s were expendable especially on top-of-the-line RVs.
Can you point me to that type of charger?

Thanks,

Malcolm
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Old 08-11-2010, 02:28 PM   #8
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I'm not coming up with the specs for the charger - is there nameplate details on it, voltage, amperage, wattage and such? I seem to remember they are small numbers, 400 watts charging?
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Old 08-11-2010, 04:42 PM   #9
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Here's a programmable voltmeter with alarm outputs. You could set the "alarm" point to the point at which you want the generator to shut off, then wire the relay outputs accordingly:

PD695 4 Digit RMS AC Voltmeter
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Old 08-12-2010, 01:11 AM   #10
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I'm not coming up with the specs for the charger - is there nameplate details on it, voltage, amperage, wattage and such? I seem to remember they are small numbers, 400 watts charging?
I meant can you suggest a DC to DC charger - not the specs for my charger.

I did a little web surfing and ran across what might be just the thing for limiting voltage for charging. The website seems to have some inaccuracies relative to the part numbers but the one in the link I am pointing to I think is actually the one that has a 20 amp capacity. That should be just right for my generator which is rated at 20 amps. I have a call in to the tech people to see if they feel it will work for my application and to clarify the part number issue on the page. See what you think.

Charge Controllers - Voltage Regulators

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Old 08-12-2010, 01:12 AM   #11
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Here's a programmable voltmeter with alarm outputs. You could set the "alarm" point to the point at which you want the generator to shut off, then wire the relay outputs accordingly:

PD695 4 Digit RMS AC Voltmeter
That seems like a good idea. I am not seeing any pricing on this unit though. Do you have any idea what it might be?

Thanks,

Malcolm
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Old 08-12-2010, 03:13 PM   #12
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Probably a couple hundred bucks.

Also, I came across these today which are probably cheaper and more suitable for what you're doing:

http://www.macromatic.com/literature...vap_series.pdf

You would want the VAP012D or VAKP012D. Newark has them in stock for $80. Newark has the sockets, too, for another $10 or so.

They only adjust up to 14 volts but for AGMs that's about right and you can put a 4.7 ohm, half watt resistor in line with it if you have to bring the trip point up a little.
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Old 08-12-2010, 04:25 PM   #13
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Wow Malcolm - those optimas are more sturdy than I remembered...

1st - the generator perhaps has very little output filtering - and if it did the capacitors then were small and wouldn't last these years - I wonder what AC ripple is coming out of the unit, the 18V you saw might've been 'phantom' from poor filtering, and from the "Rapid Recharge" specs below you have a great setup already! (IF you address adding some output filters, sealed batteries usually hate AC ripple)


Optima Spec Sheet Data:

Alternator: 13.65 to 15.0 volts

Battery Charger (Constant Voltage): 13.8 to 15.0 volts; 10 amps maximum; 6-12 hours approximate

Float Charge: 13.2 to 13.8 volts; 1 amp maximum; (indefinite time at lower voltages)

Rapid Recharge: Maximum voltage 15.6 volts. No current limit as long as battery (Constant voltage charger) temperature remains below 125F (51.7C). Charge until current drops below 1 amp.

Cyclic or Series String Applications: 14.7 volts. No current limit as long as battery temperature remains below 125F (51.7C). When current falls below 1 amp, finish with 2 amp constant current for 1 hour.

Recharge Time: (example assuming 100% discharge – 10.5 volts)
Current Approximate time to 90% charge
100 amps = 35 minutes
50 amps = 75 minutes
25 amps = 140 minutes
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Old 08-12-2010, 10:02 PM   #14
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Wow Malcolm - those optimas are more sturdy than I remembered...

1st - the generator perhaps has very little output filtering - and if it did the capacitors then were small and wouldn't last these years - I wonder what AC ripple is coming out of the unit, the 18V you saw might've been 'phantom' from poor filtering, and from the "Rapid Recharge" specs below you have a great setup already! (IF you address adding some output filters, sealed batteries usually hate AC ripple)


Optima Spec Sheet Data:

Alternator: 13.65 to 15.0 volts

Battery Charger (Constant Voltage): 13.8 to 15.0 volts; 10 amps maximum; 6-12 hours approximate

Float Charge: 13.2 to 13.8 volts; 1 amp maximum; (indefinite time at lower voltages)

Rapid Recharge: Maximum voltage 15.6 volts. No current limit as long as battery (Constant voltage charger) temperature remains below 125F (51.7C). Charge until current drops below 1 amp.

Cyclic or Series String Applications: 14.7 volts. No current limit as long as battery temperature remains below 125F (51.7C). When current falls below 1 amp, finish with 2 amp constant current for 1 hour.

Recharge Time: (example assuming 100% discharge 10.5 volts)
Current Approximate time to 90% charge
100 amps = 35 minutes
50 amps = 75 minutes
25 amps = 140 minutes
I am not following all of what you are saying here but I am catching most of it. Are you saying that I am basically OK as is with perhaps some minor adjustments? Is there any chance that my Xantrex XADC 60A charger might furnish some filtering capability as part of what it does? It is connected to the same power line after all. Otherwise what would I add to provide the necessary filtering? Are there commercially available units that I can just plug in?

Malcolm
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