Convert 120V to 12V

[mtofell1]

I Just got a macerator to empty tanks at home and am a bit stumped on powering it. I know I can pull right off the battery but am wanting to run it off my house/shore power. Reasons being I have two tank outlets on my 5th wheel so wiring up to both is a hassle. Also, I mainly bought this thing just to avoid lines at dump stations and so if I use my RV at home I can dump. I may wire up the RV at some point but for now I'm just looking for home use.

Anyway, I'm so familiar with house wiring that I'm embarrassed to even be asking these questions. I've installed electric panels in houses and wired too many things to count (I'm a building inspector by trade so I even got all the permits to ensure I did it right :))

So, what I'd love to find is a simple device I could plug into my outlet at home and wire up the two legs of this macerator to. In searching I'm getting confused by all the terms - transformer, inverter, converter - 12V, 24V.

I've got to think the part I need is simple to find but an internet search seems to just turn up inverters (I know what this is and know it's going the wrong way). From what I do understand I think I need a transformer - like for a doorbell, but the 20A rating and wire size on this macerator tell me I need way more than something for a doorbell.

Thanks for any advice.

[MEXICOWANDERER]

Ummm, with direct current is it not the rule the fewer the watts, the less the heat?

What does, and does not (Ewwww) make it successfully through the grinder makes required watts an issue. Overkill versus (Ewwwwwwwwwwwwwwwwwwwwww) clogging is therefore heavily biased in my book.

[SoundGuy]

mtofell1 wrote:
I think I ended up with a pretty good setup - 25' 10 gauge "generator" cord at Lowes for $46. It's a pack of 4 conductors so combining 2 each side gives me approximately 7 gauge (per an online calculator for combining conductors).

Since you've now purchased cable the point is moot for you but may be of use to others ... I've been using a 20' run of 12 gauge zip cord to power my own FloJet for 10 yrs now with no issues at all, speed isn't any different than it would be when connected directly to the battery, works just fine. Yes I know, the manufacturer specs 12 gauge for 10' runs and 10 gauge for 20' but I had some 12 gauge on hand so that's what I used - no motor overheating, just works as it should. :B

[MEXICOWANDERER]

And it will be flexible and easy to roll up. Good tip about Lowes.

[mtofell1]

I think I ended up with a pretty good setup - 25' 10 gauge "generator" cord at Lowes for $46. It's a pack of 4 conductors so combining 2 each side gives me approximately 7 gauge (per an online calculator for combining conductors).

[valhalla360]

mtofell1 wrote:
So, if wiring off the battery I'm seeing wire size recommendations from 8 to 14 gauge in the last handful of posts. Online I found some voltage drop tables but they talk about different % (3% table, 10% table, etc.). Does anyone have an opinion as to what table is used for the motor in this macerator? There seems to be a pretty big difference depending what table is used.

Something I did not know from a lack of DC wiring knowledge is the drastic wire size increase necessary when traveling distance. In houses it rarely is an issue unless pulling a feed to an outbuilding. Sometimes, with a very large house you might put a second panel at an opposite end. But I've often suspected the 2nd panel is as much about convenience for the electricians as it is voltage drop due to long runs.

It's not an AC vs DC thing.

It's an amperage thing. The higher the amperage, the more losses. Since 12v is 1/10th of 120v, for the same power, you are pulling 10 times the amperage. This results in much shorter runs before voltage drop becomes an issue and you have to up-size the cable.

This is a big part of why many other countries run 240v household AC. It allows smaller cheaper wires to be used. 120v or 240v, if you lick the live ends, it's not a good thing, so not much safety difference. Only reason the USA doesn't switch is everything is set up for 120v.

Remember to take the full round trip when using the tables to calculate the length (If you coil up 50' of cable in the circuit, that counts towards the length)

I wouldn't use the 10% table. If you are fully charged it can work OK but if the battery is down, it tends to compound. Say you use 10AWG copper.
- 12.7v (fully charged battery) @ 20 amps = 254w with 9.45% voltage drop with 11.5v at the motor. The motor will run a little warm but likely will survive if you don't use it a lot.
- 12.0v (45% charged) with 10% voltage drop results in 24amps and 12% drop end result 10.56v at the motor and that will be hard on the motor and being weaker, may result in greater likelihood of jamming on solids.

The site below has a nice explaination:
https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity


Edit: My calculations assumed 30' roundtrip, so 15' from battery to motor and I see you just posted 20' w/ 12AWG. That should result in around 12.5% voltage drop or 10.48v at the motor if the battery is at 12.0v. Bump up to 8AWG and that gets you 5% drop or 11.4v at the motor.

I would jump up at least to 8AWG and might even consider 6AWG but that does get pretty big and costly.

[time2roll]

I would have #6. Marginal cost is very small.

[mtofell1]

Also, just noticed the amp rating stamped on the motor is 16A but the manual lists everything for 20A.

[CA_Traveler]

At 12.7V 10% drops the motor voltage to 11.4V.

Use 8 ga.

[mtofell1]

25' run, 20A

3% is telling me 8 gauge
10% is telling me 12 gauge

Seems like a pretty big difference. I bought a 12 gauge cord today but am not sure it's the right one for the job.

[CA_Traveler]

Use 3%, 20A, 12.7V, copper wire, wire length and what does the calculator indicated for gauge?

Yes, use a online calculator.

[MEXICOWANDERER]

With DC it is a real pain to maintain adequate voltage over a long distance. My issue with macerator is this...

With varying loads (don't ask) 17 amps at the motor may be a dream in worst case. I demonstrated this to a fellow in a Crown bus conversion. His bus was 12 volt. At the macerator motor he was getting 10.9 volts while his house batteries were registering 12.7 with the converter charging them up.

I applied 14.8 volts, the macerator speed ramped way up and the fellow got the concept rapidly. He exchanged his 12 gauge wires for 8 gauge (about a 30' run) then checked with me again. "Cuts the time needed about in half".

There are 2 pin high amperage sockets and plugs in case you wish to have a macerator with a short DC pigtail.

[mtofell1]

So, if wiring off the battery I'm seeing wire size recommendations from 8 to 14 gauge in the last handful of posts. Online I found some voltage drop tables but they talk about different % (3% table, 10% table, etc.). Does anyone have an opinion as to what table is used for the motor in this macerator? There seems to be a pretty big difference depending what table is used.

Something I did not know from a lack of DC wiring knowledge is the drastic wire size increase necessary when traveling distance. In houses it rarely is an issue unless pulling a feed to an outbuilding. Sometimes, with a very large house you might put a second panel at an opposite end. But I've often suspected the 2nd panel is as much about convenience for the electricians as it is voltage drop due to long runs.

[theoldwizard1]

Pipeman wrote:
I made up a longer set of wires and attach them to the macerator wires with alligator clips. I hook them up to my 12 volt batteries in the trailer and pump into the 35 gallon black water tote that I have or into the house when at home. When dry camping I usually have the gennys running and at home the 5er is hooked up to a 30 amp plug to keep batteries charged. Simple.

Simple ! Elegant !

I would use at least 14 gauge wire, 12 would be better. Also, for heavy DC loads like that, install a set of Anderson PowerPole 45A connectors close to the batter bank with a 30A inline fuse. Couple of bucks on eBay.

[wa8yxm]

To SoundGuy. THe O/P wants to use a converter.. I don't.

To the O/P.. Now that I recall it. back before I got the wiring and jack installed to make it easier to battery power it off the RV..

I used a JUMP START battery pack. All RVers should have one and keep it charged.. THey are very useful for many things

THe one I have now is operating my main slide out due to a controller failure. Works great.

Heaven forbid I run all the batteries in the RV down again (Did it once) Jump pack has the oomph to fire up ye old ONAN and recharge.

Runs portable battery operated fan

RUns other stuff.

Very nice device.