Scamp 12v Charging on Road Question - Page 3 - Fiberglass RV


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Old 08-14-2014, 06:25 PM   #29
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Originally Posted by Steve L. View Post
Or think of this fine gentleman, think of your alternator as filling the cup (the battery charge). If he's drinking faster than.... Oh never mind.
Errr... Steve... Is that a recent or an older selfie?
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Old 08-14-2014, 06:59 PM   #30
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I'm pretty sure I sort of butchered my explanation. But from the alternators perspective the house battery is a load, the TV accessories are a load, the TV battery is a load.

If the alternator can't produce the amps for the regulator to maintain voltage greater than charge voltage of house battery it won't gain charge, if the load is running high enough the alternator output won't be able to maintain voltage above house battery and battery will lose charge.

Fridge heating element won't stop being a load no matter what the voltage is, it won't get as hot at lower voltage so fridge won't work as well and below a certain threshold probably won't cool much if any.

Going from #12 to #8 won't improve the alternator output so it won't "solve" an alternator power deficit. In terms of just charging the house battery going down the road that .2 volts is all benefit. Roughly 8% higher voltage near as I can figure. Especially useful if the stock alternator is designed to meet the load of the vehicle accessories which are running and your trying to put a charge in the house battery you just spent the last couple of days running down.

I thought I read that the more amps one runs through a wire the greater the voltage drop. If I have it correctly #12 would have around twice the voltage drop as #8 at 10 amp draw. This does not take into account the alternator/regulator working to keep the voltage at a constant target voltage. Not sure how that all plays out, especially if I have to do math.

I am not an EE or even electrician so this is just my somewhat fuzzy understanding. I would rather have folks with more knowledge clarify my fuzzy so I can learn than have bad information out there.
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Old 08-14-2014, 07:14 PM   #31
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10 gauge is wimpy. Use 8 for ground and B+ if you want to run a high draw fridge. You want all those yummy volts coming out of the end of the wire. You may have to trim some strands off the 8 ga. to fit into the 7 pin connector, but it won't hurt the performance, since resistance is additive by length.
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Old 08-14-2014, 07:20 PM   #32
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Originally Posted by Steve L. View Post
Or think of this fine gentleman, think of your alternator as filling the cup (the battery charge). If he's drinking faster than.... Oh never mind.
Steve,
I think he is getting a full charge! He learned a long time ago you need large diameter hoses.
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Old 08-14-2014, 07:40 PM   #33
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I think you are on the right track, it's all about sensed voltage. As the alternator senses that the combined voltage of the two batteries in parallel with each other reached optimum value, it starts reducing it's output voltage, therefore it's charging current.

As a vehicle battery will reach full charge quickly after a starter cycle, the higher voltage of the vehicles battery raises the average voltage of the two battery's and reduces the voltage (and available current) to the coach battery, resulting in a lower than desired charge current to the coach battery.

This, combined with the 8-10 amps needed by the refrigerator, results in drawing down the coach battery while, at the same time, the charge voltage (current) to the coach battery is lower than needed. phew.....
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Old 08-14-2014, 08:02 PM   #34
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Gauge 10 12v wire running from TV battery to 7 pin connector (about 20' in length) runs 3-way refrigerator and charges trailer battery just fine while driving. #10 ground wire to 7 pin connector comes from the closest ground point in the trunk area of the TV.
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Old 08-14-2014, 08:13 PM   #35
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I think that is the nub of the question. What is the perceived voltage by the alternator. Followed by its capacity to raise that voltage. Someone mentioned Kirchhoff's voltage law as determining the voltage at the charge wire. Might that determine the voltage being responded to by the regulator?

When I think of the batteries as load the TV battery becomes a non-load pretty quickly in that it gets up to the voltage the regulator is shooting for in a short period of time. Except absent a diode one way bridge what keeps the TV battery from contributing voltage if the circuit voltage is lower than the battery.

Put another way without isolation how would the house battery go dead and not the TV battery?

Someone needs to start filling my hat faster. If I'm going to have this headache I should have had more beer.
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Old 08-14-2014, 08:39 PM   #36
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Ok gentlemen, I'm completely lost. But I am most definitely smiling and completely entertained with your cerebral banter.

What a bunch of great guys!


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Old 08-14-2014, 08:41 PM   #37
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Quote:
Originally Posted by Bob Miller View Post
As a vehicle battery will reach full charge quickly after a starter cycle, the higher voltage of the vehicles battery raises the average voltage of the two battery's and reduces the voltage (and available current) to the coach battery, resulting in a lower than desired charge current to the coach battery.

This, combined with the 8-10 amps needed by the refrigerator, results in drawing down the coach battery while, at the same time, the charge voltage (current) to the coach battery is lower than needed. phew.....
Raising vehicle battery voltage increases current flow to the trailer's battery and refrigerator. The Ohm's law. Sure the charge voltage on the trailer battery will always be slightly lower than TV battery voltage because of refrigerator's draw, but it will be enough to continue the charging. The thicker the wires are, the lesser will be the difference in voltage.
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Old 08-14-2014, 09:51 PM   #38
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We have a deep freeze at home. We stock 64oz juice bottles filled with water(or tea) in the freezer.
We chill the fridge on shore power before a trip then place some of these bottles in the fridge along with food stuff.
We often still have ice after 5-7 days.
We also have cold water, iced tea or lemonade to drink as they thaw!
I almost never use the 12V setting on my fridge.
My Tow vehicle does keep my battery charged for lights, television, DVD, furnace, fantastic fan, etc.
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Old 08-14-2014, 10:30 PM   #39
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Quote:
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Amps times Amps = ???
Power Formula sez: Amp times Volts = Watts
Voltage drop over a distance is relative to current flow and is not a fixed value.
I (current) x R (resistance) = E (voltage drop)
With reference to the fridge heating element.
My point is that as the Voltage drops the Current decreases.

As a result the power decreases because Power = Current times Voltage.

Also Voltage equals Current time Resistance.

As a result by substitution power equals Current times Current times Resistance.

The effect of dropping voltage is felt twice because when the voltage drops the current drops as well. Regardless power is also equal to current times current times resistance.

Roger and others,
I agree you want to be as efficient as you can be but to go from #12 to #10 wire only buys you a 1/10th of a volt at 10 amps.

To me it's not worth replacing wire to get a 1/10th of a volt on 20 feet of wire. If we're talking about an even shorter ground line it makes less sense.
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Old 08-16-2014, 05:45 PM   #40
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I don't know about charging, but I know I have 12V running back from my Tug to the Scamp (while under way). I have not had a battery hooked up since getting the Scamp several months back. Feeling that the A/C might work better with a little more air flow across the coil I installed a smallish auxiliary fan behind the unit. It is 12v and I put a switch up in the closet so it could easily be turned on and off. Last week leaving our last camp I forgot to turn it off, but since I do not have a battery it quit when I unplugged from shore power. I never knew it was running the whole time going down the road as it stopped each time I stopped the tug along the way, Had I not made a quick stop and not shut the Tug off I would not know it was running yet (when under way).
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Old 08-16-2014, 07:29 PM   #41
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Time to wire in a "on" or lighted switch
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Old 08-18-2014, 10:10 PM   #42
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I'll have to try this on my trip in two weeks. I've never ran it on 12v.

I don't forsee an issue, but I could be wrong. 10 gauge wire and a 130 amp alternator should provide everything it needs.


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