It was surprisingly hard to find 500+watts of steady load around the house that still fit within the limits of my inverter (10ish year old Vector 700/1400 watt unit). Everything was either too big (e.g. heaters) or not constant duty cycle for a few hours.I finally ended up with a 250w heat lamp, 100w lamp, fan and stereo. So I have my fully powered campsite in the backyard, off the grid.The kill-a-watt started off at 501w of load but reads 493w as the voltage drifts down. The Turnigy is currently reading 53 amp draw and 599w at 11.26 off my second favorite 12v supply, a 2 year old Duralast 115Ah marine battery. Voltage drop from the battery to the inverter is .09v (I was worried about the small gauge wire on the turnigy but it is very short, then a little run of 4 gauge on one lead). Ring terminals on all connections.Not really worried about the exact timing or load profile on this battery as it discharges, though it is interesting to see how well it is keeping voltage up under a sustained load. This is a dry run for the same test on the AGMs.Waiting a little longer, 10.87v and 65.5 amp hours tripped the alarm at a bit over a 54 amp load. Time for a recharge.Jim

500 watt quartz construction lamp works great for load testing generators and the like. $10 at HD/Lowes/WW

Geat idea. Mine broke in out last move and I really miss it anyway.Testing has begun on the AGMs. I relooked at the Deka constant discharge curves. These batteries stay at above 11v to 90-95% discharged. Have to watch that. someone not paying attention could run them way too low and the inverter is never going to make a peep. I only plan to run to about 30% discharge.Jim

Here is the curve I got at higher load than my earlier tests. Volts vs amp hours removed. Test ran for 70 minutes.Seems to agree pretty well with the Deka published constant amperage curves. Interestingly even though it was constant wattage, it is a 50A discharge curve to within almost 1% because of how tightly the batteries held the voltage once they started giving power to the inverter.Jim

On my setup of three 85AH batteries I will run my batteries down to around 12.0VDC which should be pretty close to 50% charge state and then start re-charging. Going all the way to 10.5VDC I think would be much harder on my batteries. Usually my daily drain on my 600WATT PSW Inverter is around 300 WATTS (24AMPS) between 8PM to 11PM and then 1-2AMPS for the rest of the time when camping off the power grid. I re-charge my batteries back up to their 90% charge state and can do these 50%-90% discharge states for around 10-12 cycle times before I want to fully charge the bank to their full 100% charge state. My batteries seem to keep performing at full specs doing it this with my setup.My bigger problem is usually being allowed to run my generator for more than a couple of hours in the morning and maybe three hours in the early evening at most camp sites to get my 10-12 50%-90% charge cycles for three hours completed each day. Then when I need to re-charge to a full 100% charge it takes a good 12 hours or so of generator run time and I can't find a camp ground that will allow me to run my generator this long at most camp grounds. This is usually when we go home. Only place I can run a generator for 12-hours continuous is the Natl Forest areas but only during the day light hours (8AM to 8PM).just my thoughtsRoy Ken

Roy from 90% to 100% for you is something like 25.5 amp hours, correct? Ok more because that last 10% is hard. You could use a small DC-DC charger from another battery like your tow vehicle or a jump start battery to do this over night if your loads are not too high. You could also pull one battery out of the bank, and use it to top off the other two, rotating which one each day for 3 days. Or alternately pull one out and use the other 2 working batteries to top charge it. Just rotate evenly.I love cheap little $10 eBay boost converters for this kind of job. Gensets and even solar are kind of sad at top charging where you need lots of hours but not many amps (well, unless you have mega solar that gets you out of bulk early in the day). Batteries with an extremely efficient buck converter are very good at it if you have hours in your day where loads are minimum for a while.Jim

Backyard boondocking - 600w load test | Good Sam Community

31 Replies

mena661
Explorer
May 26, 2013
pianotuna wrote:
Hi Jim,

So which inverter? I'm still lusting over a 3000 watt continuous. No room for a Victron, so I'm looking for another "stackable" unit.

I'll eventually change all eight batteries. Four of mine are now eight years old and four are nearly four years old. The choice may be between marine trolling or agm. I'll most likely stick with 12 volt jars.
I would suggest Mastervolt inverters but I think they may be physically the same size as Victron. Not even 80% sure on that. Worth a look though.

http://www.mastervolt.us/
HiTech
Explorer
May 26, 2013
Raw data:

May 25,2013

Time, amps, volts, watts, amp hours, watt hours
Start, 0,12.91,0,0,0
7:10,49.4,12.10,605.8,.421,7.1
7:11,50.001, 12.12, 604.5,1.359,18.4
7:12,49.757,12.14,604.2,2.085,26.0
7:13, 49.688, 12.15, 604.0, 3.017,30.6
7:14, 49.554, 12.16, 602.5, 3.948, 49.9
7:15, 49.536, 12.16, 602.7, 4.670, 58.7
7:16, 49.524, 12.16, 602.6, 5.496,68.7
7:17, 49.531, 12.16, 602.6, 6.322, 78.8
7:18, 49.552, 12.16, 603.0, 7.35, 91.3
7:19, 49.568, 12.16, 603.1, 8.108, 102.6
7:20, 49.596, 12.16, 603.0, 9.110, 112.7

Time, amps, volts, watts, amp hours, watt hours
7:22, 49.637, 12.16, 603.5, 10.867, 134.0
7:24, 49.663, 12.15, 603.7, 12.396, 159.2
7:26, 49.704, 12.15, 603.8, 14.488, 178.1
7:28, 49.711, 12.14, 603.9, 16.146, 198.2
7:30, 49.753, 12.14, 604.2, 18.012, 220.8

7:35, 49.847, 12.12, 604.3, 22.578, 276.2
7:40, 49.909, 12.10, 604.1, 26.840, 327.8

11.97 at inverter, 12.09 at battery

Time, amps, volts, watts, amp hours, watt hours
7:50, 50.110, 12.05, 603.9, 36.114, 439.8
8:00, 50.246, 12.00, 603.2, 44.791, 544.2
8:10, 50.430, 11.95, 602.5, 53.705, 652.2
8:20, 50.592, 11.89, 601.8, 62.546, 756.3

8:21, 0, 12.35, 0, 62.848, 757.9
8:22,0,12.41,0,62.848, 757.9

Based on my earlier results I expect to put 72.1 Ah back in to get back to where I was, replacing the 62.848 drawn in the test, which I believe was still not quite charged. It Took multiple amp hours to get from 12.89 to 12.90 before the test, and over 3 ah to get from 12.90 to 12.91 which was the starting point for this test.

Jm
HiTech
Explorer
May 26, 2013
I understand all to well :)
pianotuna
Nomad III
May 26, 2013
Hi Jim,

30 amps is exactly what I want.
HiTech
Explorer
May 26, 2013
The only research I have done is looking at specs for units others have posted just out of casual curiosity. The three interesting thresholds for me are power plus margin to run coffee maker, microwave or AC. I guess the last even sillier one is 30 amp of AC for everything.

So far just making due with my old 700 watt (1400 surge) Vector.

Jim
pianotuna
Nomad III
May 26, 2013
Hi Jim,

So which inverter? I'm still lusting over a 3000 watt continuous. No room for a Victron, so I'm looking for another "stackable" unit.

I'll eventually change all eight batteries. Four of mine are now eight years old and four are nearly four years old. The choice may be between marine trolling or agm. I'll most likely stick with 12 volt jars.
HiTech
Explorer
May 26, 2013
For a tiny bank like mine they were not terribly expensive. Now when you need lots of amp hours, it adds up. :)

Jim
pianotuna
Nomad III
May 26, 2013
Hi Jim,

AGM are impressive units. Now if I did not have a beer budget....
HiTech
Explorer
May 26, 2013
Looks awesome but this is a lease. The EcoBoost is a great engine (I am a SHO fan from the original Yamaha SHO from 1989) bit I leased it just to be sure it would hold up. If the alternator blows it is Ford's problem. If it hangs in there I will buy the next one.

My '95 Yamaha SHO engine (the last year with a manual and the Yamaha engine) with serious mods and an LSD, that's my problem :)

Jim
mena661
Explorer
May 26, 2013
You could use that remote bridge rectifier setup MEX was talking about a few months ago. That way you could still keep the inverter and batteries in the RV.

http://alternatorparts.com/quicktifier-external-bridge-rectifier.html#order

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Backyard boondocking - 600w load test

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