Posted: 5/3/2014 2:28:43 AM EDT
|
I'd like to get an inverter for use in my van. I'd like to be able to use power tools while on the road.
The van is a 2014 Sprinter and it lists this for the battery and alternator: Battery: 12 V/95 Ah, alternator 14 V/200 A What size inverter would my charging system be able to handle? |
|
That 200 amp alternator rating is probably at some pretty fast engine speed. At engine idle, it'll be just a fraction of that amount.
Also, the maximum output current is usually specified when the alternator is cold. It'll be less as the alternator heats up, or when operated in hot weather: 
Assuming you aren't running other high-drain vehicle accessories (headlights, air conditioning/heater blower, rear window defroster, windshield wipers, heated seats, etc.), your engine probably won't be demanding more than 10-20 amps from the alternator - which will leave all its remaining current available for powering the inverter. Assuming your 200 amp alternator actually produces 100 amps at idle (warm), and your engine requires 20 amps of that amount, you'll have 80 amps available for the inverter. Normal alternator output voltage is around 14 volts. 80 amps X 14 volts = 1,120 watts. Assuming your inverter is 85 percent efficient at converting that DC power into AC power: 0.85 x 1,120 watts = 950 watts So........your inverter would be capable of supplying a tad less than 1 KW, continuous. Note that your battery can also contribute extra current to the inverter, albeit only for brief periods - which means that the inverter will also be able to supply more power for brief periods. Also, if you have some way of increasing the engine idle speed while you're running the inverter, you'll get more alternator output current - and thus more power out of the inverter. |
|
I'm glad I asked.
The ohms law part of it is easy for me (electrician) but I had no idea about the real output of vehicle alternators. Would it make any difference that this is a diesel engine that normally runs lower RPMs? 1,000w is smaller than expected, I see a lot of people with 2,500w inverters. I'm glad I asked before spending the money, thanks. |
|
Quoted:
Would it make any difference that this is a diesel engine that normally runs lower RPMs? Quoted:
Would it make any difference that this is a diesel engine that normally runs lower RPMs? No - Even though the engine may run slower, the pulley on the alternator is sized to spin it at the same speed as it would in a gasoline engine. 1,000w is smaller than expected, I see a lot of people with 2,500w inverters The fact that some folks have huge inverters doesn't necessarily mean that they're actually getting huge amounts of power out of them - or at least not for very long. There's no reason why you couldn't use a 2,500 watt inverter - as long as you understand that you're probably not going to be able to get 2,500 continuous watts out of it in your particular vehicle. |
| What about installing a high idle switch if it is a diesel. Drive by wire I assume. I wonder if high idle is an option on the sprinter. I know on Fire engines we can hit the high idle and it will idle around 1200 RPM and the 400A alternator is working all the warning lights, air compressor, winch,etc. |
|
There are high idle kits, at least for the previous Sprinters. But I don't want to go that far for this project.
I just figured I would pickup an inexpensive inverter to power some tools and temp lights when I need to shut the power down to a house. One of the tools I would use is the Hilti which is rated for 13A ( around 1,600w) so I wouldn't be able to power that. |
|
Quoted:
One of the tools I would use is the Hilti which is rated for 13A ( around 1,600w) so I wouldn't be able to power that. What kind of tool is it? Does it actually draw anywhere near 13 amps all the time, or is that the peak current just before it stalls? Does it run continuously, or just intermittently? Again, the rough estimate I described is for continuous power. Intermittently, your Sprinter's electrical system could probably provide quite a bit more power than that. |
|
Quoted:
small genny is the answer. I got a nice little Honda 2,500 watt generator. It's small but it's as good as any 20A circuit. But it's still 100lbs. to lift in the truck and then have to deal with gasoline and smells and noise, etc. This is my usual choice for temp power: http://i57.tinypic.com/2w3t5bm.jpg 
|
|
Wire a 2500 watt inverter to the battery and call it good. As long as you're not continuously running a load for extended periods of time, you'll be fine. When the tool isn't running, the alternator will recharge what you drained out of the battery. Most inverters come with a low battery shutdown, incase you're running a 2500 watt microwave for 30 minutes at a time, and your electrical system becomes overloaded. Now if the tool you're using is on and running a load for more than 5 minutes at a time, a generator will be necessary. For example, I would never run a greater than 5 gallon air compressor off of an inverter.
Same thing happens when people run winches, lift gates, electric hydraulic hoists for dumping, etc. The alternator is never enough to run these on their own, the battery is the gas tank. |
|
I am an electrician also, and have a Tripp-lite FC1250 (if I remember the model number correctly) installed under the passenger seat of an 07 gm van with a 6.0 liter gas motor.
It will run my little hilti, and a big te75 as well as a shop vac and a 3/4hp air compressor. It will pull the charging voltage down, but none of these items are ran for long duration. So I use the tools as needed, then leave the truck running for another 15 minutes or so afterwards. My truck burns about a gallon an hour at idle according to gm industrial. I have #2 welding cable from the batt to the inverter. |
|
Quoted:
I got a nice little Honda 2,500 watt generator. It's small but it's as good as any 20A circuit. But it's still 100lbs. to lift in the truck and then have to deal with gasoline and smells and noise, etc. This is my usual choice for temp power: http://i57.tinypic.com/2w3t5bm.jpg Quoted:
Quoted:
small genny is the answer. I got a nice little Honda 2,500 watt generator. It's small but it's as good as any 20A circuit. But it's still 100lbs. to lift in the truck and then have to deal with gasoline and smells and noise, etc. This is my usual choice for temp power: http://i57.tinypic.com/2w3t5bm.jpg OH, the noes... Dontcha know that could be dangerous? Pul-eeese don't do that... 
I like the fuse your using, the long orange thing with 3 wires in it... 
I was running a Hilti TE804 with abt 100 of 10 ga and 12 ga ext cord off a Xantrex 1800 Sinewave -this one... 
It was marginal, and I discovered a high resistance connection on the battery bank...
|
|
if you want to run tools i wouldn't run the inverter directly from the altenator. i'dd add a second battery system and run the inverter from the battery and allow the vehicle to charge the battery.
that protects your tools, your inverter and your vehicles electrical system. |