| Author |
Message |
John Elnitski
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 24, 2005 - 4:18 pm: | |
How much power does a conveter rob power when having it hooked to an inverter to run 12v devices, is it recommended to have a switch to run direct from the batteries and switch to the converter/inverter combo when batteries are dead. I have a gen set |
Brian Brown (Blue_velvet)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 24, 2005 - 4:41 pm: | |
Yes, John, it seems a waste of power to go DC-AC-DC, for sure. Your batts. supply much cleaner DC anyway.
When I bought my 80's era conversion this year, I pitched the old 30A RV-style converters and wired the fuse panels right into my house side batts. I then purchased a decent 3-stage charger for about $100 (Shumacher brand) that is constantly running when I have AC power. I have a high-amp rotary switch to select charging either batt. set from the charger. It also charges either set from the alt. when driving.
I don't have an inverter yet, since I blew my budget on a diesel genny last week. But many of the high-$ RV inverters have a built-in 3-stage charger and xfer switch. One of these days I'll break down and buy one, but my charger will get me by until then.
HTH,
Brian |
Tim Strommen (Tim_strommen)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 24, 2005 - 9:07 pm: | |
Depending on the type of inveter or converter, and the size of the load, your losses can easily surpass your final consumption.
There are a few types of converter, but I'll just name the two most common:
1) Transformer-Rectified (regulated or unregulated). These will always consume power, even when there is no load present, as the transformer is not 100% efficient (a recent DOE "Energy Star" paper states that a 75KVA transformer, about 9KW handling, will lose 400 watts with no load and ~3KW at 100% load -roughly a full third!)
2) Switching-Regulated+Rectified. These are usually more efficient, as they "switch" the power components to match the load over several ranges. This means that a designer can tune a power supply for a specific size load (with several steps in the middle) and draw as little power as needed. These can be anywhere from 78%-94% efficient (some energy is still converted into heat by the components).
Inverters. Most inverters today have the same type of components, so I'll cast aside the WAY the inverter generates AC voltage (as their efficiency ratings are around the same area). These devices take a DC voltage and invert the polarity across a transformer (typical again guys). Based on the transformer windings the voltage gets stepped up to a voltage relative to the input Inverted DC voltage (for example a 10:1 transformer will multiply your 12Volt AC signal into 120Volts AC). Now again, you'll have a transformer loss (on those inverters that have them, usually found on the quality ones...). So here again you can lose up to 25-30% (worst case).
But here's what you should use for basic estimation: As an electrical engineer, I've found as a rule of thumb that you'll lose about 25% for each conversion step you do, in addition to the minimum sustaining loss in the system. Always start this estimation from the load and work your way back to your batteries: 12Watt desk lamp (DC), throught a converter means I now need 15 watts (12 watts* 1{load}.25{loss}) to run the lamp, then back to DC with the inverter means I need to draw 18.75Watts (again 15*1.25) from the battery. The draw on this lamp is on its way to being doubled, and this doesn't even take into account line losses do to wire lengths and heat induced resistance (parasitic loss).
My suggestion for you would be to use what power you have the most of available in your rig, and just do as Brian is doing and maintain that supply with the most efficient means possible.
Cheers!
Tim |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 25, 2005 - 6:49 pm: | |
If you have an inverter, the 12 volt devices will run directly from the battery. There would be no DC loss. The inverter could be turned off if you have no need for AC power. If your connected to shore power or your genset is running the Inverter will keep your batterys charged.
Richard |
Tom Caffrey (Pvcces)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 28, 2005 - 2:03 am: | |
To add to what Richard said, if you get an inverter before you buy a charger or converter, you can do it all with one purchase, including the transfer switch. You won't need a charger or converter.
An inverter that is capable of doing just that can be bought from Camping World for around $1,200. It's easy to double that for an inverter with more features. And it's not too hard to cut it in half with an eBay deal, if you know how to buy there.
We've bought two that way and some instrumentation that really sets up a system for about 1/2 of retail.
You will need battery monitoring if you are going to have any idea about what your batteries are doing, regardless of your charging method or your source of power.
Good luck getting it all set up.
Tom Caffrey PD4106-2576
Suncatcher |
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