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Old 05-22-2018, 09:00 PM   #1
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Has any Solar Rig, with 500 watts or more, switched off Alternator.

And take some drain in power away from the engine, making it more efficient, more MPG. Think about it, if we are going down the road and getting sun, technically the Solar should be enough to charge the batteries and run the motor. But currently, if the rig is started then solar just gets disconnected because we can only have one charge controller in charge of the batteries at any given moment.

How much would be enough Solar, to justify just switching off the alternator? And put that energy back into the drivetrain. Solar is free energy, why turn it off when you turn the key.

Also, an (auto gen start) concept could be applied to the alternator if voltage drops to a determined level.
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Old 05-22-2018, 09:14 PM   #2
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I'll keep this simple , any solar is taking some load off the engine.

If your solar can charge your batteries and keep up with the electrical demand, the load on your alternator will be decreased and if the batteries are fully charged the load on the alternator should be minimal.



To keep it short you shouldn't have to manually switch the alternator on or off. The voltage regulator should do it for you automatically.
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Old 05-22-2018, 09:21 PM   #3
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And take some drain in power away from the engine, making it more efficient, more MPG. Think about it, if we are going down the road and getting sun, technically the Solar should be enough to charge the batteries and run the motor. But currently, if the rig is started then solar just gets disconnected because we can only have one charge controller in charge of the batteries at any given moment.

How much would be enough Solar, to justify just switching off the alternator? And put that energy back into the drivetrain. Solar is free energy, why turn it off when you turn the key.

Also, an (auto gen start) concept could be applied to the alternator if voltage drops to a determined level.

Interesting questing, but I am not sure part of your premise is correct. I believe you can have multiple charging sources charging your batteries. For instance, when I am plugged into shore power and the sun is shining, both my solar controller and my onboard converter/charger are charging the house batteries.


When driving down the road without the generator on only my solar panels charge my house batteries, but the alternator charges the engine battery. The reason for this in my case is that the solenoid that is supposed to connect the house and engine battery together has failed and I have not replaced it. I am not sure my 600 watts of solar could keep up with the demands of both the coach and the engine with solar only, but, like I said it is and interesting question.
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Old 05-22-2018, 11:07 PM   #4
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curious, how to turn alt off? i don't remember ever seen a switch or something.
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Old 05-22-2018, 11:37 PM   #5
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There is no switch to turn off the alternator and I don't believe that the alternator backs off when solar is there, but rather believe that solar backs off when it sees the alternator. Of course, while this would depend on the programming of the voltage regulators of both units, alternators generally don't have a "float" program, while solar chargers do. Alternators don't run for months on end and will put 14 volts or more on the battery for as long as you drive.
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Old 05-23-2018, 05:15 AM   #6
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They ignore each other and the charge rate for both is determined by the level of charge in the batteries. My GMC often only shows 12 volts on the gauge when the battery is fully charged and ramps back up when it gets a load. The solar controller will do the same.
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Old 05-23-2018, 05:44 AM   #7
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The problem with switching off the alternator is when you turn on high amp items or enough items, what's going to keep the voltage steady for the engine and transmission computers.

Wipers, fans, headlights all draw power. If you ever watched a battery monitor during a partly cloudy day, with solar, you would see how variable the output is. I've watched mine, while swinging at anchor, and just turning 45į effects it. On the road, going around a corner will change output.

If your going to be switching the alternator on and off, you better have a soft start regulator installed. Otherwise you could be burning belts off.

PS: Never disconnect a battery from a alternator while its spinning fast. It will burn out. You need to switch it off at the voltage regulator.
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Old 05-23-2018, 07:25 AM   #8
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I would not switch the alternator off even if I had a thousand watts of solar.

The alternator is a "Demand" device. kind of like the converter.. When I'm explaining the limits on how much you can run on 30 amps I mention that the converter.> Well my 9180 can draw a thousand watts or more putting it in the "Microwave" range if the batteries are run down. OR if the batteries are full it's just a few watts. (LED TV range)

Same with your alternator. IF the batteries are run down it puts out near rated current and draws considerable power off engine. But if the SOLAR has the batteries full up. the alternator is putting out next to nothing and the engine sees it more as an idler pulley than a load..

It is a "Demand" device, if there is no demand, then there is no load. and it basically shuts itself off.
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Old 05-23-2018, 08:28 AM   #9
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I would not switch the alternator off even if I had a thousand watts of solar.

The alternator is a "Demand" device. kind of like the converter.. When I'm explaining the limits on how much you can run on 30 amps I mention that the converter.> Well my 9180 can draw a thousand watts or more putting it in the "Microwave" range if the batteries are run down. OR if the batteries are full it's just a few watts. (LED TV range)

Same with your alternator. IF the batteries are run down it puts out near rated current and draws considerable power off engine. But if the SOLAR has the batteries full up. the alternator is putting out next to nothing and the engine sees it more as an idler pulley than a load..

It is a "Demand" device, if there is no demand, then there is no load. and it basically shuts itself off.



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Old 05-23-2018, 12:54 PM   #10
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i thought this over, i realized the op might have meant to "turn off loads" to alternator, rather than "turn off alternator". if so, i have been doing it for years.

my battery pack is lithium, and i don't have a starting battery (removed it to gain the space for lithium). i have 2750w solar panels to charge the battery. alternator is in place but i don't want it to charge my lithium without management system. so what i did was i set up a controller that automatically cuts off the connection between the alternator and the battery after 30 seconds of engine startup. there is button in cockpit however, a manual override, allowing alternator to charge the battery when need be, like in continuous rainy days and battery soc being low and i am driving... i have not seen ill effects yet.
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Old 05-23-2018, 01:29 PM   #11
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i thought this over, i realized the op might have meant to "turn off loads" to alternator, rather than "turn off alternator". if so, i have been doing it for years.

my battery pack is lithium, and i don't have a starting battery (removed it to gain the space for lithium). i have 2750w solar panels to charge the battery. alternator is in place but i don't want it to charge my lithium without management system. so what i did was i set up a controller that automatically cuts off the connection between the alternator and the battery after 30 seconds of engine startup. there is button in cockpit however, a manual override, allowing alternator to charge the battery when need be, like in continuous rainy days and battery soc being low and i am driving... i have not seen ill effects yet.
Your shutting off the load of the house battery bank. If I'm understanding what your doing, the alternator is still supporting the chassis loads.

If I understand him, the OP says he wants shut it down completely, and let the solar support the chassis.

Maybe I'm wrong.
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Old 05-23-2018, 01:47 PM   #12
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Your shutting off the load of the house battery bank. If I'm understanding what your doing, the alternator is still supporting the chassis loads.

If I understand him, the OP says he wants shut it down completely, and let the solar support the chassis.

Maybe I'm wrong.
actually i am shutting off the loads from "chassis" and "house" altogether (originally two cables from alternator to chassis and house. now in my system both lines are connected to the only "house", ie, "house" does both things). when my alternator is in off state, no loads to it.

i understand in a sunny day, a large solar system and a decent size battery pack can do the job, but what about night driving and in rainy days? shutting down the alternator completely without conditions wouldn't be practical.
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Old 05-23-2018, 11:09 PM   #13
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Has any Solar Rig, with 500 watts or more, switched off Alternator.

Iíve been having the same question since recently upgrading my electrical system. So I took some screen shots of my battery monitor while I was driving. Interestingly, my battery was receiving a lot more amperage than I would think makes sense based on the displayed SOC. Of note, Iíve got two Trojan T-105 REs. Click image for larger version

Name:	Image1527138414.802591.jpg
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ID:	204026 Thoughts? Seems like too much amperage hitting the batteries given the SOC. So, while I was not considering shutting down the alternator, I have been considering installing a disconnect between the Trojans and the alternator. Other note, chassis is a 2004 E-450.
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Old 05-23-2018, 11:45 PM   #14
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16.8a isn't too much, and your battery is lead-acid type, there won't be harm to keep feeding it as only as it's below than 14.8v.
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