I dunno what kind of antediluvian laptops are out there, but I just
looked at the three laptop power supplies we have here and none output
more than 2.1 amps @ 19 volts and that's 40 watts. Input power will be a
bit higher -- but just a bit because these supplies don't really get
very warm which indicates pretty good efficiency.

And again, I watch the ammeter on my aux battery pretty closely, and I
rarely see the laptop pull more than a couple amps. 24 watts.

--
RJS

On 07/31/2011 10:09 AM, Dennis Haynes wrote:
> Even a single laptop power supply can use 100 watts or more, especially with
> the laptop on and charging the battery in same.
> Yes you do have a battery problem but even with that corrected your use and
> run time with engine off is limited.
>
> Dennis
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
> Daniel Rotblatt
> Sent: Saturday, July 30, 2011 12:16 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Inverter/Aux Battery question
>
> Dennis-
>
> I didn't expect to have to use a full 400 watts - basically I just wanted to
> be able to charge some computers, etc.  I don't imagine more then 150 watts
> as a sustained load - and even then it's a luxury - i.e. if the kids are
> bored and noisy and need to watch a video, or something like that.  This
> issue is with no load on the inverter - just doesn't seem right.
>
>
> Dan
> Los Angeles, CA
> '85 Westy Weekender
>
> On Jul 30, 2011, at 4:30 AM, Dennis Haynes wrote:
>
>> This is going to be difficult to explain but there are a number of
>> things that are going against you.
>> When sizing a battery for an extended load the battery should be sized
>> for a minimum of  a 5 to6 hour discharge rate. To get 400 watts out of
>> a 120 volt inverter you need 400/12 = 33.33 Amp/Hr. Consider some
>> inefficiency and that fact that under load you will have less than 12
>> volts a full 40 A/Ah or more is required. The largest of the Yellow
>> Top batteries is 55A/Hr. over the 6 hour discharge rate. So you do not
>> have enough battery and this sustained load will damage it.
>>
>> Next problem is using a low cost inverter to charge batteries.
>> Modified sine wave inverters basically switch and filter DC to make AC
>> so most appliances can work. Motors due to their inductance do not
>> care and Most DC power supplies can clean it up enough the only bad
> effects are usually some hum or
>> buzz on audio equipment or fuzzy lines on old televisions.   However,
> cheap
>> power supplies for charging batteries use the batteries as part of the
>> filter and the peaks of the waveform pass right through them basically
>> making the batteries a heater they now have a load in addition to what
>> they actually need to charge. As such my 2002 Toshiba Laptop and a 400
>> watt inverter can take down a 60 A/Hr. battery in about 2.5 hours.
>>
>> So for all those low voltage toys and cell phones get the 12 volt
>> charger power cord for each device.
>>
>> Dennis
>>
>>
>> -----Original Message-----
>> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On
>> Behalf Of Daniel Rotblatt
>> Sent: Friday, July 29, 2011 5:17 PM
>> To: vanagon@GERRY.VANAGON.COM
>> Subject: Inverter/Aux Battery question
>>
>> Well, I just got back from a trip to Mammoth Lakes (separate post on
>> that) and got a chance to try out the aux battery and inverter I got.
>> The problem I had was that with the car off, the inverter didn't get
>> enough power to work.  When hooked up (and I tried two inverters and
>> got the same results), the voltage would drop from 12.6 to about 8.x
>> volts - not enough to run the inverter and it would automatically shut
>> off.  Thus, the only time I could charge the computers (keeping the
>> kids happy), etc., was when the car was running.  Is this how it
>> works?  What is the need for a aux battery, i could have just hooked
>> up the inverter to the main battery and not used it when the car wasn't
> going an saved $175 on the aux battery.
>>
>> Hook-up:
>> -brand new yellow top battery
>> -Stock attachement to the starting battery (had to replace the relay)
>> -Inverter hooked directly to the terminals of the yellow top - about
>> 4' of wire, (I tried just 8 gauge with about 3' of wire, and finally
>> with 3' of 8 gauge and a few feet of 12 gauge hooked to that with a
>> cigarette plug since that's what was on the inverter).
>> -Inverter is a 375 watt Tripp-lite (good reviews on amazon).
>> -Voltage at the battery (when new) was ~12.7 , with car running it's
>> ~13.6, with car not running and inverter attached it's ~8.5 -All the
>> inverters I saw shut off at a little over 10 Volts....
>>
>> So...is that what's supposed to happen or is something not right?  I'm
>> planning a trip to New Mexico next week, so it would be nice to have
>> it working.
>>
>>
>> Dan
>> Los Angeles, CA
>> '85 Westy Weekender
>>