Subaru Forester Owners Forum banner

1 - 20 of 20 Posts

·
Registered
Joined
·
160 Posts
Discussion Starter #1
I'm thinking about putting a power inverter in the centre console. Ideally, I'd like to run it on its own circuit, but as I never use the cigarette lighter, I think it would work to splice off that. I'm not looking to make extra work for myself.

I'm still in the "research" phase of this project, and will remain so until some funds can be freed up for this. With a kid on the way, that might be a while...

What I'm worried about is a couple things. First, heat. Is there any type of ventilation in there? I'd install it in the lower compartment, but if I had to, I could install a vent in the bottom to allow some circulation.

Also, I'm wondering about how to run the wires. I'm not looking for a huge power supply (somewhere around 100W), just enough to run a cell phone charger, PDA charger, or laptop power supply (which might require a lot more juice than the other two). What size wires would I need, and am I in danger of burning the fuse for the cigarette lighter? I wouldn't imagine it would, as I'm most likely going to purchase one that's designed to plug into the lighter (rather than run off the battery).

Lastly, I'd like to have a separate switch for it. I've got some extra change-holders that I never use, and I was thinking about putting in a switch (much like the seat heater switches). I don't know if I could get a two-position switch that would match the 3-position ones that are already there. If it doesn't match, then I'm not interested. A lighted switch would be even better...

I'm thinking about the best position for the outlet. Maybe in the rear of the car, behind the rear-seat cupholders. But that raises the question of liquids spilling into it. I don't want to leave the outlet on the inverter, because I'm worried that with a charger plugged in, the lid wouldn't close.

I want this to be totally hidden: i.e. I don't want to change the appearance of the car at all. I'm very interested in keeping things hidden.

I think the simplest option (but also the lowest on the "that's cool!" scale) would be to add a 12V outlet inside the centre console and just plug in an inverter when needed.

Any advice? I've read about relays, etc. and have some electronics experience, but I've never fooled with automotive electronics. Is this something that I can get myself into a lot of trouble doing? I don't want to mess up my car, as it's my only mode of transportation...
 

·
Administrator
2018 2.5i Premium CVT
Joined
·
18,832 Posts
Most of the inverters I've encountered would be a tight fit inside the console, and I think that cooling might also be a problem. How about putting the inverter under one of the seats, anchoring it there (velcro?), and running the AC wiring into the console?

100 Watts might be a bit low for your laptop.

Assuming you get a 150 Watt model, and assuming 100% conversion efficiency which is not a reasonable assumption, you would be pulling about 11 Amps at the 13.8 volt vehicle voltage. Can anybody help with a good estimate of conversion efficiency? Absent any real data, I'd tend to guess 50%, which brings you up to 22 Amps, which calls for 10 gauge wire on the 12 volt side of things.
 

·
Mr. April 2008, Image Master
2005 X
Joined
·
1,325 Posts

·
#8 Post ho
1999 Subaru Forester
Joined
·
2,441 Posts
100 Watts is more than enough for a laptop

I second the "under the seat" idea
 

·
Registered
Joined
·
160 Posts
Discussion Starter #5
I had considered that, but I'm worried about feet/dirt/liquids etc. We're not exactly the cleanest, most car-friendly family in the world... Is there enough space to tuck it up under there safely? Would it block the rear seat vents at all?

Does anyone know what guage the wiring to the DC outlet (cigarette lighter) is? Also if it's fused at any amperage? I'm worried about burning the wiring with this.

I will look into the under-the-seat application. It would most likely have to be under the passenger seat, and I might wire up an outlet in the centre console for convenience's sake.
 

·
Administrator
2018 2.5i Premium CVT
Joined
·
18,832 Posts
SenorSubie said:
100 Watts is more than enough for a laptop
The power supply on mine is rated at 150 Watts max output. Input is 100-240 Volts at 2 Amps. I've never measured the actual current draw of the computer, so I don't know whether it's actually pulling anywhere near this much power. But I do have a big screen laptop.
 

·
#8 Post ho
1999 Subaru Forester
Joined
·
2,441 Posts
I figured I'd take a peek and find out what I've been using

Mine will fit under the seat no problem, with plenty of room for air etc, and
there is a "lip" before so dirt shouldnt' be a problem, but it is inconvienent
to plug things in down there..



 

·
Registered
Joined
·
160 Posts
Discussion Starter #10
I can get adapters for everything, but the whole point is to avoid that. I don't like having to purchase new adapters every time I get a new piece of equipment - or borrow something. I find it a better idea to drop a little more money on the inverter right off the bat, and then not have to keep buying adapters...

Especially considering how much apple charges for power adapters. It's more expensive for one then for the whole inverter set up. And I'm not even sure how much I'm going to use each piece of equipment - most likely it'll always be either my cell charger or PDA charger (so I can use it as an mp3 player for long durations).
 

·
Administrator
2018 2.5i Premium CVT
Joined
·
18,832 Posts
I just scored one of the little 175 Watt Xantrex inverters that The Wraith described for an eBay bid of $20.49! Brand new. It opened at $19.99 and the other bidder just bid the opening price. Reasonable S&H too.

There's another one up in two days if anybody wants to go for it. Search for Xantrex 175. (Sounds like a medication.) Another one sold exactly two days ago, so it looks like it might be a regular offering by this seller.

I needed this win. Earlier today I was going to measure the actual conversion efficiency of another inverter in order to fine-tune my original response to this post. It smoked violently when I plugged it in. It had come from one of those return outlets that sell on eBay, and I knew I was taking my chances when I bought it. I guess I now know why it had been returned. Win a few, lose a few.
 
A

·
Guest
Joined
·
0 Posts
No sure if your car has this sort of box between front chairs. Mine has and I didn't find it usefull enough. When I was looking for inverter I was thinking about the size that may fit this box. The one I found in Radio Shark or so was about 30 CAD and has been working for about 2 years now. I power laptop, different sort of chargers for phones, camcorder etc even used it to run orbital polisher or desktop with CRT monitor. Mine is rated 170W of output and it seems anough for all my applications. And it's convenient, right under my hand. Just flip top cover, plug and turn on.
I noticed that power socket in this box as well as in trunk is a bit weaker then cigaret lighter's one (brobaly because of different wiring). Sometimes inverter starts beeping (especially when front light is on, brake pedal is pressed and car is idling. But when it runs at some reasonable speed - then no problem.
Have not noticed any excessive heating problem.
 

Attachments

·
Registered
Joined
·
81 Posts
As far as laptops and inverters, 175W is enough to run the laptop, but when the laptop battery is dead it takes much more than 175W to charge the laptop. I have a 300W inverter and it will overcurrent when the laptop battery is almost dead. If I start charging at 50% or so it is no problem. Also these inverters are thermally protected, but I wouldn't push my luck with a tight enclosure. Under the seat or in the cargo area sounds like the area to put it. If you are worried about liquids mount it to the seat frame or somewhere up off the floor, but I think that dust will be your worst enemy. No way around it, it needs ventillation. They are relativly cheap anyway.

Remember that the inverter will cause noise in the AM radio, if you listen to that. Maybe FM and other parts of your head unit. That is why most people use DC to DC adaptors.
 
A

·
Guest
Joined
·
0 Posts
One may easily check power required by a laptop, looking at back of AC/DC adapter used by the laptop. Mine says 65W.
As I mentioned before, very important to have good wiring all the way from battery to inverter. It needs more then 10A of current, so even 0.5om resistance somewhere will drop output power drastically.
 

·
Administrator
2018 2.5i Premium CVT
Joined
·
18,832 Posts
alexmolin said:
One may easily check power required by a laptop, looking at back of AC/DC adapter used by the laptop.
The wattage that you see specified on the power supply is most likely the wattage that it can deliver to the laptop at the laptop's DC voltage, not the wattage it consumes from the AC input (wall or inverter). These wattages will not be the same, due to losses in the process. That's why the power supply gets hot.

My power supply for example specifies:

- DC Output: 19v, 7.9A Max (150W max). This is the most it can deliver to the laptop. Laptop might not always need that much, depending on the state of its battery.

But

- AC Input: 100-240v, 2A, which at a typical US/CDN line voltage of 120v works out to an AC consumption of 240 Watts. This is what the power supply takes from the wall or the inverter when delivering max power to the laptop.
 
A

·
Guest
Joined
·
0 Posts
I doubt that adapter is able to dissipate 90W (equivalent of 100W light bult). It must have heat-sink with forced air then otherwise it gets melted. In fact it's just closed, air sealed box.
 

·
Administrator
2018 2.5i Premium CVT
Joined
·
18,832 Posts
The one I described above does have a fan, and it gets pretty warm in spite of the fan. But those are indeed max figures. My main point is that you need to rate your inverter by the AC draw of the power supply, not the DC draw of the PC itself, and it's most likely that the figure you see on the supply is that of the DC capacity of the supply.
 

·
Dodgy Post Whore - eh!
2003 XT 2.5 AT
Joined
·
1,825 Posts
bbottomley said:
100 Watts might be a bit low for your laptop.
SenorSubie said:
100 Watts is more than enough for a laptop
I would say it depends on the laptop. I wouldn't personally recommend going below about 150W, and if you want to charge and work at the same time you could easily be pushing it even with 150W. But have you considered working on your laptop while charging it, your phone, and PDA at the same time?

bbottomley said:
Can anybody help with a good estimate of conversion efficiency?
Typically around 85% efficient, with "good" inverters around 90%. Of course, not going direct with a DC-DC transformer for your cellphone means a second 85% efficiency exchange from the mains voltage down to cellphone charger voltage. That probably isn't a problem unless you're an efficiency freak (no offence - efficiency is good).

Also, take note of standby current, when the inverter is plugged in and switched on but doing nothing. I've seen figures from <0.3 to 0.7 amps on 300W inverters. If your battery is OK it would cope with being left overnight with that sort of load, but such a waste, even if you're not an efficiency freak.

Thanks for this thread, BTW - saved me starting one myself to discuss some of the things mentioned in posts above. However, one question I have that I didn't see addressed was the rated surge current of inverters. Is that an instantaneous surge? Or extending over a few seconds/minutes?

Edit: I've now found answers for these questions as well, since I've just got an inverter - 500W surge, 300W for 5 minutes, 250W continuous. And just 0.2A standby drain.
 

·
Dodgy Post Whore - eh!
2003 XT 2.5 AT
Joined
·
1,825 Posts
bbottomley said:
The wattage that you see specified on the power supply is most likely the wattage that it can deliver to the laptop at the laptop's DC voltage, not the wattage it consumes from the AC input (wall or inverter). These wattages will not be the same, due to losses in the process. That's why the power supply gets hot.

My power supply for example specifies:

- DC Output: 19v, 7.9A Max (150W max). This is the most it can deliver to the laptop. Laptop might not always need that much, depending on the state of its battery.

But

- AC Input: 100-240v, 2A, which at a typical US/CDN line voltage of 120v works out to an AC consumption of 240 Watts. This is what the power supply takes from the wall or the inverter when delivering max power to the laptop.
The 2A figure is probably only at the minimum 100V input, so it'll be drawing a maximum of 200W. That means that if it was being fed 240V it would only draw 0.83A for the same 200W input. Same power output with all input voltages, max 150W, which means a 75% efficient transformer at full load (which seems a tad low, but isn't too unreasonable).

I've just taken a look at my own laptop power supply and if I'm reading it correctly it says 45W output :!:
 
1 - 20 of 20 Posts
Top