Home » Public Forums » GMCnet » [GMCnet] Got my automatic transfer switch and 30A cord installed
| [GMCnet] Got my automatic transfer switch and 30A cord installed [message #268221] |
Thu, 25 December 2014 09:18  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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Senior Member |
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Hi Rob,
The issue with many of these so called "inverter" type MWs is the amp draw is way, way higher than the name plate rating. In my case with the Panasonic Inverter MW it only reached the amp draw on the name plate after 3 hours of running! Up to that point amp draw was considerably higher.
If batteries, wire, connectors and inverters were 100% efficient (they are not - more like 70% to 80% efficient) then for a given 120 vac AC amp load you would be pulling 10X that amp load from a 12vdc source. In your example, 13 amps x 120 vac = 1560 watts so to get 1560 watts out of a 12 vdc source you would need to pull 130 amps or more than 50% of the max capacity of your battery bank. In the real world your battery if fully charged would start out at around 13.2 volts and would drop rapidly to around 11 volts under that kind of load so the starting amp draw would be (assuming your system is 80% efficient) 1560 watts / 13.2 vdc = 118 amps / .8 = 147 amps which would increase rapidly as the voltage in your battery bank sagged down to 11 vdc or so, 1560 watts / 11 vdc = 141 amps / .8 = 177 amps.
Two 6 vdc batteries wired in series will yield 12 vdc at the same amp hour rating as the individual 6 vdc batteries. Two banks of two 6 vdc batteries in series which are wired in parallel will yield 12 vdc with twice the amp hour rating as the individual 6 vdc batteries. Two 12 vdc batteries wired in parallel will yield 12 vdc at twice the amp hour rating as the individual 12 vdc batteries. Since one 12 vdc battery of the typical auto size will have less than half the amp hour rating as one 6 vdc deep cycle battery of the same physical size, a bank of four 6 vdc batteries wired series/parallel will have a larger amp hour rating than four 12 vdc batteries wired in parallel. Plus, because of internal resistance issues, it is never a good idea to parallel multiple 12 vdc batteries to make a larger amp hour capacity bank, anyway. If you want a larger amp hour rating using 12 vdc batteries, use 4d or 8d size batteries which will provide around 200 to 240 amp hours each. Para
llel two of those any you will have about the same amp hour rating as a series/parallel bank of four 6vdc deep cycle batteries.
In our Royale we have 460 amp hour capacity battery bank (four large 6vdc deep cycle Interstates) and in the Clasco we have one 12 vdc 4d battery with 200 amp hours of capacity. The Royale is overkill unless you are going to dry camp for several days at a time. The Clasco is fine for occasional dry camping for a couple of days with careful use management, or an easy over night away from shore power.
If you are not sufficiently confused yet, wire size, wire length and quality of connectors on the dc side play a critical role in determining how a battery bank will perform under load. The more resistance you have in any of those the more the voltage will sag under load and hence the greater the amp draw becomes for a given watt load.
So, bottom line in running MWs off of inverters is 1) start with the most efficient MW you can find, not the cheapest, 2) don't plan on running it for more than a few minutes at a time off of the inverter - 10 minutes is about the max practical time limit, 3) size your battery bank and inverter to be able to deliver more than twice the real amp draw of the MW, and 4) use at least one size larger wire than you think you need. The other bottom line, it is easier to run the generator to run the MW.......
Hope this helps and why in the world I am writing this stuff at 7 am on Christmas morning is beyond me other than for the first time in decades Sharon and I are enjoying a laid back Christmas all by our selves! We will leave tomorrow to join in the ruckus of the more normal family Christmas with her sister's family plus part of our family in Portland. But, oh this peace and quiet is rally nice this morning.....Our best to all of you.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
Visitors always welcome!
glwork@mac.com
http://jerrywork.com
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Message: 11
Date: Thu, 25 Dec 2014 15:05:19 +1100
From: "Robert Mueller"
To:
Subject: Re: [GMCnet] Got my automatic transfer switch and
30Ampcordinstalled
Message-ID:
Content-Type: text/plain; charset="windows-1251"
Ken,
Here's the Sharpe Microwave in Double Trouble:
http://www.sharpusa.com/ForHome/HomeAppliances/Microwaves/Models/R820JS.aspx
If you go click on the Tech Specs tab you will find this:
ADDITIONAL SPECIFICATIONS
AC Power Required (Amps): 13
13 Amps X 120 Volts = 1560 Watts
The Xantrex has a 2000 Watt capacity and more on start up.
Mac has noted that my two 6 VDC batteries have total maximum of 2700 Watts.
Question: to get the microwave to run I need:
a) How many 6 VDC pairs in series for 12 VDC connected in parallel to the Xantrex?
Trojan
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] Got my automatic transfer switch and 30A cord installed [message #268224 is a reply to message #268221] |
Thu, 25 December 2014 09:45  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Jerry,
Sure glad you had a quiet Christmas morning to jump in on that -- saved me
straining my brain & I sure don't have anything to add -- except maybe to
note that most inverters seem to shut down completely at about the 11 VDC
level you mention as being so soon reached. :-)
Merry Christmas -- today AND tomorrow.
Ken H.
On Thu, Dec 25, 2014 at 10:18 AM, Work Jerry wrote:
> Hi Rob,
> ...
>
Hope this helps and why in the world I am writing this stuff at 7 am on
> Christmas morning is beyond me other than for the first time in decades
> Sharon and I are enjoying a laid back Christmas all by our selves!
...
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Got my automatic transfer switch and 30A cord installed [message #268229 is a reply to message #268224] |
Thu, 25 December 2014 10:54 |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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Senior Member |
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Ken's info below is probably the most likely cause of Rob's inverter supplied microwave oven's early shutdown. As I wrote earlier, Rob's house battery supply is very limited in power delivery. The draw of the M/W oven probably drops the battery voltage below 11 VDC from its 12.6 resting fully charged state in very short order.
We hams have problems with dropping voltage to our mobile transceivers. And that's with only a peak maximum battery draw of 30 Amps or less. Battery boosters are available to partially compensate for that. They can provide 13.8 V (desired operating voltage) with battery supply as low as 10.5 VDC. At that point, they shut down as well to hopefully leave enough battery capacity to restart the engine!
In all cases, use of extremely low resistance connections and adequately-sized primary power cables is almost as important to a ham's operation as they are in the low voltage DC wiring in RVs.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~ ~ ~ ~ TZE166V101966 ~ ~ ~ ~
~ ~ ~ '76 ex-Palm Beach ~ ~ ~
~~ k2gkk + hotmail dot com ~~
~ www.gmcmhphotos.com/okclb ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
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> From: hend4800@bellsouth.net
> Date: Thu, 25 Dec 2014 10:45:31 -0500
> To: gmclist@temp.gmcnet.org
> Subject: Re: [GMCnet] Got my automatic transfer switch and 30A cord installed
>
> Jerry,
>
> Sure glad you had a quiet Christmas morning to jump in on that -- saved me
> straining my brain & I sure don't have anything to add -- except maybe to
> note that most inverters seem to shut down completely at about the 11 VDC
> level you mention as being so soon reached. :-)
>
> Merry Christmas -- today AND tomorrow.
>
> Ken H.
>
>
> On Thu, Dec 25, 2014 at 10:18 AM, Work Jerry wrote:
>
>> Hi Rob,
>> ...
>>
>
> Hope this helps and why in the world I am writing this stuff at 7 am on
>> Christmas morning is beyond me other than for the first time in decades
>> Sharon and I are enjoying a laid back Christmas all by our selves!
>
> ...
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| Re: [GMCnet] Got my automatic transfer switch and 30A cord installed [message #268243 is a reply to message #268229] |
Thu, 25 December 2014 15:25 |
Hal StClair
Messages: 971
Registered: March 2013
Location: Rio Rancho NM
Karma: -12
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Senior Member |
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Another thing I've noticed about MW ovens is that they don't like square wave inverters. They (mw's) make at lot more noise and take appreciably longer to heat. The true sign waves let them run like the grid or genset. Sure saves battery power.
Merry Christmas all,
Hal
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane."
1977 Royale 101348,
1977 Royale 101586, Diesel powered,
1974 Eagle Bus 45',w/slideout,
Rio Rancho, NM
[Updated on: Thu, 25 December 2014 15:27] Report message to a moderator |
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