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Old 08-14-2020, 03:14 PM   #1
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Power supply in lieu of dump light

This is a bit of a cross-post (sorry) from a thread in the tank forum where I was asking for options to wire a Flojet portable macerator pump I just bought. If you don't know what it is, it connects to the 3' dump, macerates the bad stuff and pumps it up to 100ft away.

As I was looking for potential power supplies, I noticed the dump light right by the dump station. I took it off and noticed it's connected to the line that powers the water pump among others, with a 15A fuse in the box. The wire gauge seems decent and the existing hole in the underbelly looks like may fit a SAE quick connect socket like this one: https://www.amazon.com/CERRXIAN-Weat...dp/B07TB7XH2H/.

If I could do this, it would be nothing but perfect as it would make using the pump super convenient, with no alligator clips and wires running to the battery box.

As the pump needs 20A, it looks like I would have to upgrade the fuse. Would it be reasonably safe to do so? Is there anything else I may be missing that would set my AS on fire?
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Old 08-14-2020, 03:18 PM   #2
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Interesting idea. I will be looking forward to seeing what those who are in the know think.
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Old 08-14-2020, 05:13 PM   #3
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15 amp fues is normally on 14 ga wire. If you use a 20 amp fues the wire needs to be 12ga. Don't want to melt anything.
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Old 08-14-2020, 05:30 PM   #4
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YouTube full timers "Changing Lanes" did a video on this, but didn't mention wire gauge. I'd think you'd want a 12 ga wire because the pump seems to work pretty hard.
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Old 08-14-2020, 05:51 PM   #5
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Originally Posted by A W Warn View Post
15 amp fues is normally on 14 ga wire. If you use a 20 amp fues the wire needs to be 12ga. Don't want to melt anything.
Thanks - I'm not sure what's the gauge of the wire in the AS harness, however I just got the pump: the wires are labeled 12ga and they definitely seem smaller than the ones I have in the AS. The socket I linked to above is 10AWG. I'm guessing that if the smallest gauge is at the pump I should be fine?
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Old 08-15-2020, 12:42 PM   #6
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I would just try running it with the 15 amp fuse, perhaps a “slow blow” type, like for the A frame jack, I like the connector you found.
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Old 08-15-2020, 02:14 PM   #7
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NEVER 'upgrade' a fuse without ensuring the wire is adequate fore the rating of the fuse. Fuses are put in the circuit to protect the wiring. If you put a higher amperage fuse, the wire may become the fuse and could possibly start a fire.
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Old 08-15-2020, 03:00 PM   #8
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I would go for it and use the 15 amp fuse. Some of the smaller garbage disposals work on 15 amp circuits. A macerator pump serves the same function further down the line, with you doing the hard work of pretreating the garbage.

The only potential trouble I see would be running another appliance, such as the water pump, simultaneously on that circuit, popping the breaker.


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Old 08-15-2020, 04:46 PM   #9
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I believe Airstream uses 12 ga. wire throughout the trailers, at least they did that in mine. You said yours is the same circuit as the water pump. They typically require 7-8 apps so don't use both at the same time. On my Flowjet I use my lithium battery booster for power. It works great. It is also a good backup power source for the Relax Awning.
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Old 08-17-2020, 10:45 PM   #10
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Well, so far so good. The adapter arrived and it sits perfectly in the dump light pre-drilled hole. It took me probably 5 minutes to fish out the main cables, verify they are indeed 12GA and connect them to the adapter. I kept the 15A fuse: the pump description claims 20A, but the sticker on the motor says 16A so I may have some leeway.

The pump started! My tanks are empty now so I didn't put it through a real test, but it should work. I'm now just missing a bit to drill pilot holes in the skirt to secure the adapter then I should be able to post a pic for those interested.

I'm pretty happy with the result so far though, plugging in the pump is a breeze and I love that I don't have to lug long extension cords to the battery or a separate power supply that needs tending to.
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Old 06-30-2022, 05:16 AM   #11
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Can you provide an update on this approach? I am looking at taking the same approach. My main issue is the low mounting location of the Airstream discharge. I want to be able to pump into my "poo cart" without having to mess with using the flex pipe to get everything into poo cart.

Note that the power draw for any pump increases with flow rate, so for my application, I will be restricting the discharge flow so that I draw less amps (my pump shows a 12A draw).
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Old 06-30-2022, 05:33 AM   #12
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Note that the power draw for any pump increases with flow rate, so for my application, I will be restricting the discharge flow so that I draw less amps (my pump shows a 12A draw).
Iím not sure thatís the right approach.
In my limited experience, when an electric motor is free wheeling it draws the least amps. When the load is increased, amps increase.
Putting a restriction on the discharge side is resistance that the motor will see as a load, and will work harder to overcome, drawing more amps.
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Old 06-30-2022, 05:51 AM   #13
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Quote:
Originally Posted by CivilEngr
Note that the power draw for any pump increases with flow rate, so for my application, I will be restricting the discharge flow so that I draw less amps (my pump shows a 12A draw).

Restrictions are like equivalent lengths of pipe in a head loss chart. Or just static head. Throw it in hazen-williams eq and see what you get.
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Old 06-30-2022, 05:55 AM   #14
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One thing to consider is that amps go up as voltage goes down. If you're running your converter while the pump is running you'll keep the voltage higher, therefore the pump will draw less amperage. Trying this with low voltage in the batteries (like after a long night of dry camping) would have the opposite effect.
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Old 07-01-2022, 06:42 AM   #15
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Iím not sure thatís the right approach.
In my limited experience, when an electric motor is free wheeling it draws the least amps. When the load is increased, amps increase.
Putting a restriction on the discharge side is resistance that the motor will see as a load, and will work harder to overcome, drawing more amps.
I must admit that as a civil engineer for the past 40 years, this has always seemed strange to me too! You throttle back a pump or huge fan and it certainly sounds like it is working harder - but the amp draw goes down. Maybe this small crappy (pun intended) pump my react differently - I will check with an ammeter at different conditions.
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Old 07-01-2022, 06:51 AM   #16
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For my application, I won't be pumping more than 10' horizontally and 1' - 2' vertically, so there won't be any significant head on the pump. Restricting the flow into the poo cart will make the filling process less exciting!
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Old 07-01-2022, 06:54 AM   #17
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One thing to consider is that amps go up as voltage goes down. If you're running your converter while the pump is running you'll keep the voltage higher, therefore the pump will draw less amperage. Trying this with low voltage in the batteries (like after a long night of dry camping) would have the opposite effect.

I just upgraded to a 400 A Lithium (Battleborn) system, so the small amount of draw from this pump shouldn't have any impact.
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Old 07-01-2022, 07:54 AM   #18
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I just upgraded to a 400 A Lithium (Battleborn) system, so the small amount of draw from this pump shouldn't have any impact.
I was thinking more about the wiring and fuse than the batteries. Sounds like you have it covered though.
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Old 07-01-2022, 08:07 AM   #19
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When most pumps run with the discharge wide open they tend to cavitate. When you pinch down on the discharge, the discharge pressure increases and stops the cavitation making it run smoother.
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Old 07-01-2022, 03:05 PM   #20
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Also depends on which discharge is being restricted. If restricting the discharge from tank into pump or discharge out of pump.

Note restricting discharge from tank into pump would increase risk of blockage.
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