I have a laser printer that I've been wanting to use on the go in the car with an inverter.

The power consumption section in the printers manual:

Average operating mode    Less than 310W
Ready mode                Less than 30 W
Power save mode           Less than 1.2 W
Power off mode            Less than 0.45 W (0.1 Wc)

I bought a 500W inverter for the car thinking this would be adequate. I connect up the inverter and the printer, the printer turns on, and then just as it hits its warm up process the inverter trips and everything stops. My first thought is that the cars wiring doesn't like pulling ~500W through the cigarette lighter socket... even though the fuse didn't blow. I then connect it directly to the battery under the bonnet and the same thing happens. Out comes the multi meter, I set it to measure DC amps and connect it in series between the car battery and DC side of the inverter and press the power button on the printer watching it intensely for a spike just before it dies. As expected the multimeter reads something like ~7.3x.

Now, my question is, how many Watts is the printer using at this point in time?

  1. is it 12V (input voltage) * 7.3A (input amps) = 87.6W
  2. or is it 230V (output voltage) * 7.2A (input amps) = 1656W
  3. or something else?

It seems right to multiply the volts and amps using measurements from one side of the inverter (1.) but it can't be using 86.4W otherwise I wouldn't have an issue. However, multiplying a measurement from one side of the inverter with a measurement from the other side (2.) doesn't seem right, but it's giving me an answer that seems more realistic to me.

Any clarification on the matter is gratefully received.

  • \$\begingroup\$ You definitely want to check the supply current while your printer is heating up, the power drawn will be much higher than average. Are you using an RMS meter, as the measurement may very well differ from the real value. Also notice the difference in VA and Watt, the VA rating here is very important too. Probably best results will be obtained with a real sine wave inverter. \$\endgroup\$
    – jippie
    Oct 30, 2013 at 7:17
  • \$\begingroup\$ +1 for "switch to an inkjet", but i'd also be interested in folks' insights on whether a gas generator would fare any better. \$\endgroup\$ Apr 8, 2016 at 6:11
  • \$\begingroup\$ I had some problems with my inverter because the cables/connectors were not good enough for the high peak current draw, i.e. that the voltage drop over the cables becomes so much that the inverter trips an under-voltage event. Probably you really do need to buy a 1500w pure-sine inverter though. \$\endgroup\$ Jan 23, 2017 at 22:49
  • \$\begingroup\$ Most UPSes, even up to 1000 VA have a warning not to connect laser printers to them for exactly this reason. Peak warm up power draw from a laser printer is extremely high. \$\endgroup\$
    – Evan
    Dec 6, 2018 at 0:20
  • \$\begingroup\$ I'm voting to close this question because it is an off-topic query about the use of consumer electronics, and attracts abuse of the answer form by those asking similar questions. \$\endgroup\$ Dec 6, 2018 at 0:20

7 Answers 7


you can try and measure the peak current by monitoring the current while the printer is connected to the mains power,(caution about 230Vac). As there won't be a breaker dropping out you should be able to see the current drawn through the complete cycle of the printer.

However I caution you about measuring current on the 230Vac.

It does sound like the peak load at warm up is outside the peak that your inverter can provide.

The heater that is being turned on would have a low cold resistance and hence draw more than its running current when first switched on.

  • 2
    \$\begingroup\$ Last laser printer I dismantled used a long halogen lamp sort of thing as the heater, so it will have a sizeable current spike at startup. Plus most cheap inverters are quite nasty & use about 6dB's worth of marketing bullshit in their specs. \$\endgroup\$
    – John U
    Oct 30, 2013 at 17:14
  • \$\begingroup\$ @JohnU Yeah, I've noticed the marketing crap that surrounds the cheaper inverters too. \$\endgroup\$
    – OdinX
    Oct 30, 2013 at 19:56
  • \$\begingroup\$ @TomGeorge I though about measuring it when its on mains, one question though, my multimeter is labelled for DC Amps, should I have an AC Amps option or is it the same/safe to use the DC option? One last thing, could you tell me which value (Watts) was correct and why? Thanks \$\endgroup\$
    – OdinX
    Oct 30, 2013 at 20:01
  • 1
    \$\begingroup\$ You'd need AC amps, AC clamp meters are V.cheap these days. Also, you don't say if your inverter is a standard "pseudo-sine" type - 99% of them are, they put out a pretty nasty square wave as opposed to a smooth sine wave you get from the mains. This can upset some equipment and is generally unhelpful. \$\endgroup\$
    – John U
    Nov 1, 2013 at 9:26

I have the same problem. Not realizing the huge current required to run a laser printer, I've incrementally bought bigger inverters and smaller laser printers with no success. Running a laser printer from your vehicle, it turns out, is an expensive proposition neither the printer manufacturers nor the low end inverter manufacturers will warn you about.

As a mobile technician I need to be able to print from my truck so I can have the customer sign a printed work order when I'm done. I may have a job in Pennsylvania followed by a last minute assignment in Maryland, West Virginia, and Virginia or DC. Searching for, and driving to a Kinkos, FedEx, or UPS store to find a printer enroute is a PITA. In southeast DC, Hoodbridge VA and parts of PG County in MD you don't even want to stop at traffic light, let alone get out just to print a document. Additionally, I often need drawings, schematics and checklists up on a scissor lift, a ladder, a man lift and bucket truck. Quickly printing out the latest and greatest revision on-site to carry up with me in paper form reduces the danger (and expense) of dropping the laptop or tablet on someone's head.

According to Don Rowe you'll need a pure sine wave inverter with 1,500 Watt capacity such as the Samlex SSW-1500-12A, costing about $350. This is five times more expensive than the $69.99 750W Schumacher inverter X175DU I got from Walmart and almost 4 times the $89 price of a Samsung Express M2830 laser printer I got on sale from Staples.

  • 8.8 amps * 120 volts = 1,056 Watts for a purely resistive heating element in the fuser. Some laser fuser elements are inductive (use the VA unit instead of W). You may be able to get away with a 1KW inverter instead of a 1.5KW. Either way you ain't going to be able to simply plug into the cigarette lighter. You're going to have to do some heavy duty cabling directly to the battery routed through a hole in the vehicle firewall, another expense and something to potentially fail.

  • Due to sensitive electronics in the laser printer, a square wave or pseudo sine wave inverter is not recommended.

You might want to just give up the laser printer idea altogether and try an inkjet printer. Using the wattmeter built into my Schumacher, a HP Deskjet F4180 doesn't even measure any power use at all. I can run both my laptop and the printer without having to run the engine to charge up the truck battery for an hour or so.

Note: carry jumper cables if your inexpensive (cheap) inverter keeps going when the battery voltage drops below a certain threshold.

Another benefit of a deskjet, besides its low power consumption, are the pretty color pictures you can print, albeit not as quickly or with as fine a resolution as a laser printer.


Laser printers have very high peak power needs, manufacturers tend to quote average power usage.

Power consumption   135 watts

During Printing: At nominal line voltage.   
  Model A (120V): Maximum of 700 W, Average of 210 W 
  Model AB (240V): Maximum of 625 W, Average of 210 W

Inrush Current: (Duration: significantly < 1 second)    
  Model A  (120V): 23 A peak (20 deg C, from cold start) 
  Model AB (240V): 40 A peak (20 deg C, from cold start)

enter image description here

See https://superuser.com/a/466645/52492

700 W from 12V is 58 Amps (+30% for inverter inefficiency?). You may need to run heavy cable to the vehicle battery (via a suitable fuse). If averages are a guide, your laser printer may have 2.5 times the peak power needs as quoted in this example.


Use an NTC termistor on your AC output. It will limit the inrush (peak) current when you start the printer.

This only works if there is only 1 peak current and only at startup. If there is a peak current every time the heating ellements are switched on then this won't work. Once the NTC is warm, it won't limit peak currents anymore. I don't know if printers have peak currents every time or only when they're cold.


In this case, the power (Watts) consumption would be determined on the input side. The reason for this is that if you measured voltage and current coming out of the inverter, you would have only the power provided by it, and not the total power your circuit is consuming, because the inverter does not have perfect efficiency. So you are in fact, at the moment the multimeter measures it, using 12V (input voltage) * 7.3A (input amps) = 87.6W of power. However, there could be a momentary spike you're missing that is much much higher current. Note that your printer's manual specifies "Average" operating mode, it says nothing about the peak! In addition, make sure your inverter's power rating is continuous, and not peak. For example, this inverter is listed as 500W, but if you read the fine print, you can see it only supports 300W continuous output power. Your issue may be a combination of these factors.

As a side note, in the US, most cars are rated for 100-120W on the cigarette lighter port. I suspect the circuit breaker in your inverter is blowing faster than any fuse your car has for that port.


The problem is that your printer documentation specifies only average power consumption, and not peak power consumption. On the other hand, your inverter is an electronic device, so it might not be able to provide much more than the nominal power figures, not even for a very short time. Most probably your inverter has a built-in current limit (either on the primary side, or on the secondary side), and the peak inrush power required by your printer makes the inverter bump into its current limit, thereby limiting the output voltage. Since the printer has a switched-mode power supply, whatever voltage it gets, it wants to suck up the needed power - this quickly makes the inverter recognize the load as a short, and it simply turns off.

I don't think you could measure the real power needed by the printer using that inverter, because of the current limit I mentioned. Instead, you might want to connect the printer to a normal household socket, and measure AC current/voltage there. Your multimeter should be quick, as the peak probably lasts only a second or even less. Trying it several times might give you a clue about the magnitude of the peak. If had to guess, I'd say an inverter of at least 1000-1500W would be needed even for a smaller laser printer.


Your printer requires a "pure sine" ac current flow. Your cheap inverter is putting out an incomplete wave, which fools the printer into registering incorrect voltage. You can destroy a printer this way. Follow the advice above and get a Deskjet, or shell out $1500.00 for a pure sine inverter, deep cycle 12V accessory battery and controlling circuitry/HD wiring. You may need a 160+ Amp alternator as well.


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