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Old 07-20-2017, 11:53 PM   #1
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Macerator blowing 20 amp fuses

So I had to, for the third time, replace the 20 amp fuse for the Macerator. As with the other occasions, it instantly blows on activation as I don't even hear the motor starting.

After some pain, found the manual for the Flojet pump they use and it says 20 amp is the right fuse. And that maximum current usage is 16.5. My sense is that though the initial start up current is much higher causing the fuse to blow.

After replacing the fuse it runs fine for multiple clean ups. Last time we flushed it was just 10 days ago so stuff had not sat there for too long.

Anybody else see this problem?
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Old 07-21-2017, 10:02 AM   #2
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So I had to, for the third time, replace the 20 amp fuse for the Macerator. As with the other occasions, it instantly blows on activation as I don't even hear the motor starting.

After some pain, found the manual for the Flojet pump they use and it says 20 amp is the right fuse. And that maximum current usage is 16.5. My sense is that though the initial start up current is much higher causing the fuse to blow.

After replacing the fuse it runs fine for multiple clean ups. Last time we flushed it was just 10 days ago so stuff had not sat there for too long.

Anybody else see this problem?
More than likely there is hair or other debris on the rotor, and it is causing the motor to draw more amps when it starts up. I had to replace my pump when it blew one of the nuts holding on the endcap. But what I did see when I removed the end cap was a lot of hair wrapped around the rotor. So be sure to use a strainer in the shower if you use it for that purpose.

The only way to tell is to remove the pump and take the end cap off the macerator.

Another possible suspect may depend on what type, if any, of sanitation fluid or packets. It has been reported that the dissolving packets will not dissolve completely, and can also cause headaches in the pump. I never use them so I can't really say.

Finally, Airstream's poor design of the sewer system allows fluid to always remain in the pump because the pump is lower than the outlet unlike other manufacturer's where the pump is at least the same plane as the bottom of the tank. What goes up, does not go out when the hose becomes partially empty and starts pumping air. This liquid just sits there, day in and day out, and it can't be good for the health of the pump. I modified my Interstate and after each use, I can drain the entire 3" hose so the pump won't sit in water for months on end.

Finally, it just also may be just a bad pump motor, bearing, or other defect.

The cure is to simply replace the pump. I am on my third pump after 6 years.
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Old 07-21-2017, 04:44 PM   #3
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We had a similar issue when we first got our AI. It appeared to be a combination of too much toilet paper and not enough liquid in the tank when we dumped. After that we made sure that prior to dumping there was plenty of water in the black tank. No further issues for the past three years (knocking on wood).
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Old 07-21-2017, 05:03 PM   #4
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You can use a slow blow 20 amp fuse.

Same protection but protects fuse from very sure term current spike if it blows you have a problem as described in post above.
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Old 07-21-2017, 06:20 PM   #5
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We had a similar issue when we first got our AI. It appeared to be a combination of too much toilet paper and not enough liquid in the tank when we dumped. After that we made sure that prior to dumping there was plenty of water in the black tank. No further issues for the past three years (knocking on wood).
That makes sense. Still I think it is a poor design where the system is functional regardless even though it blows the fuse.
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Old 07-21-2017, 06:21 PM   #6
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You can use a slow blow 20 amp fuse.

Same protection but protects fuse from very sure term current spike if it blows you have a problem as described in post above.
I know about slo-blo fuses but I don't think they come in automotive blade configuration that is used in AI. So I would have to re-wire it to use an in-line glass fuse.
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Old 07-21-2017, 10:41 PM   #7
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So I had to, for the third time, replace the 20 amp fuse for the Macerator. As with the other occasions, it instantly blows on activation as I don't even hear the motor starting.



After some pain, found the manual for the Flojet pump they use and it says 20 amp is the right fuse. And that maximum current usage is 16.5. My sense is that though the initial start up current is much higher causing the fuse to blow.



After replacing the fuse it runs fine for multiple clean ups. Last time we flushed it was just 10 days ago so stuff had not sat there for too long.



Anybody else see this problem?


Have you checked to see if the macerator impeller is free with a screwdriver in end of motor shaft slot? Procedure is in maintenance section of your owners manual at about page 9-16.

This will tell you if the pump is jammed by something and usually can be cleared with a few twists of screwdriver.
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Old 07-22-2017, 11:54 AM   #8
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I have not but as I mentioned, it runs just fine with a new fuse. So the stickiness is super slight and it frees it on its own.
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Old 07-22-2017, 12:58 PM   #9
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So I had to, for the third time, replace the 20 amp fuse for the Macerator. As with the other occasions, it instantly blows on activation as I don't even hear the motor starting...

Anybody else see this problem?
For ten years, I've had a macerator pump on my little 1955 airframe trailer. Recently it began blowing fuses. Believing that the peak amp draw when the pump activated was the culprit, the solution was to install a relay in the circuit, which seems to have solved the problem.

Michael
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Old 07-22-2017, 10:13 PM   #10
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Slow blow auto blade type fuse are FSK ATO

Here is one listed for $1.90

http://www.mouser.com/ProductDetail/...hHmSl1xw%3d%3d
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Old 07-23-2017, 07:31 AM   #11
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What does one do if on a trip the macerator fails? Is there an emergency procedure to drain the tank if it is not working?
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Old 07-23-2017, 10:58 AM   #12
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Slow blow auto blade type fuse are FSK ATO

Here is one listed for $1.90

http://www.mouser.com/ProductDetail/...hHmSl1xw%3d%3d
Thanks. Unfortunately I think that is a mistake on Mouser web site. If you look at the spec sheet at littlefuse (http://www.littelfuse.com/products/f...fuses/fks.aspx), you see that they label them as "FKS Series - ATO® 32V Fast-Acting Automotive Copper Blade Fuse.

Indeed if you look at the specs, they are identical to fast blo fuses. At 200% current for example, minimum trip time is 0.15 seconds which is the same for both types.

Slow blow glass fuses are made with much thicker elements that I suspect doesn't fit in such small footprint as blade fuses.

I think the proper protection for this is a DC circuit breaker, not a fast blo fuse.
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Old 07-23-2017, 11:44 AM   #13
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Macerator blowing 20 amp fuses

Quote:
Originally Posted by amirm View Post



I think the proper protection for this is a DC circuit breaker, not a fast blo fuse.

Agreed. I believe that is what's used on the big Class A rigs that have a macerator.
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Old 07-23-2017, 04:25 PM   #14
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Thanks. Unfortunately I think that is a mistake on Mouser web site. If you look at the spec sheet at littlefuse (http://www.littelfuse.com/products/f...fuses/fks.aspx), you see that they label them as "FKS Series - ATO® 32V Fast-Acting Automotive Copper Blade Fuse.
No. They are slow blow. Go to the original link. Click on the underlined link "FKS ATO" in the chart on the left of the page and you will find that Littlefuse defines every fuse on the chart as as slow blow.

The price tells me that they are not common fast blow fuses.
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Old 07-23-2017, 04:39 PM   #15
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No. They are slow blow. Go to the original link. Click on the underlined link "FKS ATO" in the chart on the left of the page and you will find that Littlefuse defines every fuse on the chart as as slow blow.

The price tells me that they are not common fast blow fuses.
They are higher grade fuses but their specs are identical to fast blo fuses from little fuse.

Here is the spec page for standard mini fuses:



Notice the trip time table on bottom right. Now the FKS one:



As you see they are identical. And I quoted directly from littlefuse web site in my other post where they refer to them as fast acting.
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Old 07-23-2017, 05:08 PM   #16
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I still beg to differ. The term "FKS ATO" describes a specific style of fuse and does not describe every fuse Littlefuse makes in that style. The image below is direct from the Littlefuse website and specifies those particular part numbers as slow blow..

I don't know what the timings are for the slow blow version, but I do know they are not as described in the previous images.
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Old 07-23-2017, 08:26 PM   #17
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Anybody else see this problem?
Getting away from the issue of fuses because that argument could continue forever otherwise, there are some tricks I have picked up to help the macerator pump work better and with fewer problems (I've only blown 1 macerator fuse in 5 years so I can't contribute to that argument anyway, darn it!):
1 - Before dumping the black tank, top it off with HOT water by using the handheld shower head to fill the tank through the toilet. In my case, I also modified the exterior shower to be able to hook up the shower hose to the black tank flush fitting so I could give the tank a hot-water rinse after dumping (the flush fitting has a check valve, plus I added another to the hose, so no worries about back-contamination). Hot water in the black tank helps soften organic solids. I even thought (briefly) about re-plumbing the toilet to flush with hot water all the time, but laziness overcame ambition.
2 - Add some dish soap to the empty black tank at the start of the trip and after every tank dump. Dish soap reduces water surface tension, and again helps soften or even dissolve water-soluble solids in the tank.
3 - Add a removable screen to the shower drain. The screw-in sink stoppers have slotted drain screens built in, but the shower drain doesn't. And since you can not only get hair down the shower drain, but whatever you track in on your shoes or feet when you use the bathroom (a drawback of a wet bath), the shower drain screen will do wonders to keep out stuff that can clog the pump.
4 - Use only quick-degrading RV toilet paper. Folks who dump through a slinky don't have to be so meticulous about choosing the right paper, but we macerator pump users have to be careful about choice. Or better, don't even put used toilet paper in the black tank, put it in the wastebasket. But not everyone is comfortable with that.
5 - If you use a tank deodorizer or tank treatment, choose a liquid type rather than a powder packet, so there is no plastic wrapper to end up in the black tank.
6 - Always use the black tank flush fitting to rinse out the black tank after dumping the black tank. As noted above, hot water works better if you can use it, but even a cold rinse is better than no rinse.
7 - Pull out all of the hose even if the dump station is only 3 feet away. Water (or ground-up solids) trapped in the coiled-up hose can cause significant back-pressure on the macerator pump if you don't pull it all off the reel each time.
8 - Never dump the black tank by itself. Always dump the gray tank after the black tank (and always top off the gray tank before dumping, same as with the black tank), so that no solids are trapped in the pump to clog it up for next time.
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Old 07-23-2017, 11:04 PM   #18
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Thanks for words of wisdom as always Protag. Great to see you back!

We don't use the shower so no issues with that. On Toilet, I just have my wife keep her foot on the pedal for a minute or so and then I pump that out too. The outcome is almost clear water coming out of the black tank. Have been too lazy to flush it with the hose.

We do use RV toilet paper as it is the same thing we use at home for our septic. The only gray water we produce is from washing our hands and teeth. We don't do any cooking, washing dishes, etc. on the RV.

While on this topic, when I pump the black tank, it all comes out filling the hose. When pumping the gray tank, it has plenty of air gaps. Is this normal?
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Old 07-23-2017, 11:32 PM   #19
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While on this topic, when I pump the black tank, it all comes out filling the hose. When pumping the gray tank, it has plenty of air gaps. Is this normal?
Yes, because the gray tank contains one thing the black tank doesn't— soap. That means bubbles in the water.
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Old 07-24-2017, 08:39 AM   #20
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6 - Always use the black tank flush fitting to rinse out the black tank after dumping the black tank. ....
The first (and so far only) time we used the black tank flush it broke something and (thankfully fresh) water spilled out into the coach. Be very careful to use minimum water pressure from the city water source.
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