Forum Discussion

jornvango's avatar
jornvango
Explorer II
Mar 14, 2022

What size inverter do I need?

Our Casita trailer has one Duracell AGM battery and a 100V Renogy portable solar panel. By 11 AM, the battery is typically 100% charged so we don't use all that much (I presume). Inside the RV, we use LED lights and other than that, the 3-way fridge and water pump use the RV battery, as well as us charging an iPad and cell phone by using the 12V outlet in the RV.

Now ... for charging my laptop while we're traveling, I bought a (cheap) 400W inverter at Walmart to plug into the RV's 12V outlet. Since the laptop charger is 90W, the solar panel barely keeps up while the laptop is charging during the day, but it works fine.

Question: I want to use my electric hair clipper, perhaps once every two weeks for 10 minutes, to keep my hair short. The hair clipper says on the back "120V AC 60Hz 8W".
When I plug it into the 400W inverter however, the blades don't move fast enough to cut my hair. It works but it hurts my head while cutting so I can tell it needs more 'power' to run faster as intended.
Can anyone tell me how big of an inverter I should get if 400W isn't enough?

Is it accurate to say that the hair clipper needs 120V and a 15-amp outlet so 120x15 = 1800W to run as intended and I only have 400W at the moment?

Thanks! (Yes, I'm challenged when it comes to electricity)

Jorn
  • valhalla360's avatar
    valhalla360
    Navigator
    Mar 17, 2022
    MrWizard wrote:
    Your problem is voltage drop, going to the inverter because the wiring going to the 12v outlet is too small or your battery is not getting fully charged and is slowly dying, 8w at 12v is only 0.75 amps add in inverter conversion loss and is still only 1.0 amps or 12'watts power use,
    I suggest you try connecting the inverter directly to the battery, and maybe do your hair cut late in the afternoon just before the end of charging cycle when the battery is at its peak for the day, or maybe plug your inverter into your tow vehicle and cut your hair, even run the engine if need be , 10 minutes every two weeks should not be a strain or a financial drain from fuel costs


    If the 8w is correct, it's unlikely to be a voltage drop issue. As you say, that's only 0.75amps plus a little for the inverter to operate. Voltage drop comes into play when you try to force a lot of amps thru too small of a wiring system.

    Also, the OP says the battery is hitting full charge, so his battery should be fine.

    Yes, connecting with short fat cables to the battery is better but voltage drop is unlikely to be the issue.
  • MrWizard's avatar
    MrWizard
    Moderator
    Mar 17, 2022
    Your problem is voltage drop, going to the inverter because the wiring going to the 12v outlet is too small or your battery is not getting fully charged and is slowly dying, 8w at 12v is only 0.75 amps add in inverter conversion loss and is still only 1.0 amps or 12'watts power use,
    I suggest you try connecting the inverter directly to the battery, and maybe do your hair cut late in the afternoon just before the end of charging cycle when the battery is at its peak for the day, or maybe plug your inverter into your tow vehicle and cut your hair, even run the engine if need be , 10 minutes every two weeks should not be a strain or a financial drain from fuel costs

    I have run hair Clippers, pet trimmers, box fans, table fans drills, vacuum cleaners, from inverters for many years,
    Most cases power to the inverter is the cause of problems, in my previous RV I ran a residential 120vac compressor fridge on MSW inverter for ten years , the current owner has used it for 4 years , the inverter and fridge are now 14 yrs old and still work,.I doubt the type and size of inverter is the problem,
    Try my suggestions and post back with the results
  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    Mar 15, 2022
    ewarnerusa wrote:
    jornvango wrote:
    ...
    Now ... for charging my laptop while we're traveling, I bought a (cheap) 400W inverter at Walmart to plug into the RV's 12V outlet. Since the laptop charger is 90W, the solar panel barely keeps up while the laptop is charging during the day, but it works fine.
    ...
    Jorn

    The laptop needs 90 watts to charge and that is a fixed variable, but you could find a 12V charger for your laptop to plug into the Casita's 12V outlet and leave the inverter out of it. That takes away the conversion loss associated with inverter efficiency. This is hardly going to save the day, but just something I wanted to point out. Doing it the way you're doing it, you're converting 12V DC to 120V AC, then converting 120V AC to whatever the laptop brick does (probably 19V DC?).


    X2!

    I have mentioned this in the past but most folks here seem reluctant to use a 12V car charger for laptops for some odd reason :h



    You do not have to buy one specifically for your laptop brand, there are "universal" chargers which will set the voltage and amperage for your laptop by selecting the correct plug for the charger.

    Found HERE for $36..

    The one in the link is what I bought for my DDs Dell i7 "two in one" laptop/tablet which I added a SSD drive to.. DD exclusively uses the universal charger since it can plug into 12V for in car use/charging or at home it plugs into 120V outlet..

    Going direct means you are not double converting (IE 12VDC to 120V AC and then 120V AC to 18V-20V DC) which adds more wasted battery capacity.

    For very small draw items like cellphones, tablets that use 5V USB chargers, consider using cig lighter plug type 12V car chargers which take 12V DC directly to 5V DC..
  • ewarnerusa's avatar
    ewarnerusa
    Nomad
    Mar 15, 2022
    jornvango wrote:
    ...
    Now ... for charging my laptop while we're traveling, I bought a (cheap) 400W inverter at Walmart to plug into the RV's 12V outlet. Since the laptop charger is 90W, the solar panel barely keeps up while the laptop is charging during the day, but it works fine.
    ...
    Jorn

    The laptop needs 90 watts to charge and that is a fixed variable, but you could find a 12V charger for your laptop to plug into the Casita's 12V outlet and leave the inverter out of it. That takes away the conversion loss associated with inverter efficiency. This is hardly going to save the day, but just something I wanted to point out. Doing it the way you're doing it, you're converting 12V DC to 120V AC, then converting 120V AC to whatever the laptop brick does (probably 19V DC?).
  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    Mar 15, 2022
    valhalla360 wrote:
    Lwiddis wrote:
    A Jackery is about as an expensive solution as you could find. (It’s a battery!) Add another solar panel and another RV deep cycle battery. Consider Lithium.


    From his description, he has plenty of solar and battery already. He just needs a way to convert that into something that will run the clippers.

    It would be silly for him to spend a ton of money building a system that he doesn't need.

    The rechargeable clippers should take care of the issue...and simply plug them in and see if they charge off the cheap inverter (don't leave the inverter running all the time). Otherwise, charge them when you are on shore power.


    Sometimes it is the simple low cost solutions that work the best. Rechargeable battery powered clippers? Yep, solves that problem.. Should be able to get multiple uses before needing recharged.
  • valhalla360's avatar
    valhalla360
    Navigator
    Mar 15, 2022
    Lwiddis wrote:
    A Jackery is about as an expensive solution as you could find. (It’s a battery!) Add another solar panel and another RV deep cycle battery. Consider Lithium.


    From his description, he has plenty of solar and battery already. He just needs a way to convert that into something that will run the clippers.

    It would be silly for him to spend a ton of money building a system that he doesn't need.

    The rechargeable clippers should take care of the issue...and simply plug them in and see if they charge off the cheap inverter (don't leave the inverter running all the time). Otherwise, charge them when you are on shore power.
  • jornvango's avatar
    jornvango
    Explorer II
    Mar 15, 2022
    Thanks for the advice, I went to Walmart and bought a cordless hair clipper. That will be much cheaper than severely upgrading the electrical system in the RV.

    I guess the reason I didn't buy a pure sine wave inverter was that I didn't shop around. I just went to Walmart and bought what they had available.

    Regarding avoiding buying an overpriced jackery, our Casita doesn't have any roof space available for installing a solar panel, so we use a portable 100 watt solar panel at the moment. I do realize that a jackery which is basically a battery with a built-in inverter, is more than what we need. If I can just add a second battery and another solar panel to the casita, we will be all set. However, I'm not sure how long we will keep the Casita so I like the idea of the jackery being portable into our next RV solution.
  • TurnThePage's avatar
    TurnThePage
    Explorer
    Mar 15, 2022
    Lwiddis wrote:
    A Jackery is about as an expensive solution as you could find. (It’s a battery!) Add another solar panel and another RV deep cycle battery. Consider Lithium.
    This is what I would do. If you could install the panels on the roof, it would be almost no maintenance or thought there after.
  • theoldwizard1's avatar
    theoldwizard1
    Explorer II
    Mar 14, 2022
    KD4UPL wrote:
    Modified sine wave inverters are like black and white televisions. You could buy one but why?

    Given modern technology, there should less than $50 difference on a less than 1000W modified vs pure sine wave inverter.

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