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Date:         Mon, 1 Aug 2011 00:25:12 -0700
Reply-To:     Daniel Rotblatt <d.rotblatt@VERIZON.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Daniel Rotblatt <d.rotblatt@VERIZON.NET>
Subject:      Re: Inverter/Aux Battery question
In-Reply-To:  <BAY152-ds4B4EB87666CD5CD9F67BBA0390@phx.gbl>
Content-Type: text/plain; charset=us-ascii

Dennis,

You're right, computers can take 60-100 watts charging power. That's about .6-1 amp/computer - not a heck of a lot. Even so, I never expected to have to run the computers (or whatever) for too long. The beauty of laptops is they do have their own batteries with 2-3 hours charge in them. A small fan for desert heat might also be nice at night - the smallest I saw only took about 40 watts - or .4 amps. Either way, I'm not running anything big or necessary on it - it's a convenience and when it needs a charge I'll stop using it and that's fine. I just figured that I'd be able to run something on it with the engine off!

Hope I don't sound cranky - I do appreciate the info - all is appreciated, and I'll see what kind of run time I get on the upcoming Santa Fe trip (assuming fixing the posts works...).

Dan Los Angeles, CA "Winky" the '85 Westy Weekender

On Jul 31, 2011, at 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 >>


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