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Post by joerolando2701 on Mar 21, 2017 19:57:37 GMT -8
Hoping someone can help me out here. I've got a pretty good handle on the 110 end of the camper wireing I understand how the inverter, autoswitches, AC to DC converters etc work what I'm wondering is what connects the battery into the 12v system while keeping it isolated from it while on shore power? I get the 110 comes in from shore power then goes to the control panel/converter/charger then you got 110 with breakers out and 110 converted to 12vdc fused out that's feeds all the 12v stuff in the trailer. So what makes the battery run the 12v when shore power is disconected. I'd like to run my inverter into a autoswitch to switch between shore and battery but I've heard you don't want to run your converter of a battery which is of course pointless anyway since it's already 12v but with a combo unit that's a little tricky so how do I switch between 110 converted 12v and battery 12v
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Post by joerolando2701 on Mar 21, 2017 20:56:30 GMT -8
Just wondering does the battery back feed through the converter/charger to feed the dc system when shore power is disconected and receive power to charge when shore power is connected?
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Post by vikx on Mar 21, 2017 21:21:52 GMT -8
The converter allows the battery to take over when the trailer is off grid. The battery either provides power when off grid or the converter is charging it when on shore power thru the same hot wire. Today's newer converters have "smart chargers" that will protect the battery and won't overcharge.
Inverters drain the battery quickly and larger ones require a battery "bank" to provide any sort of decent 110 power. Some of the smaller inverters (cigar plug operated) will supply a c-pap machine for a couple of days but not much more. Maybe a light bulb or two, maybe charge your phone.
I think the autoswitch/inverter may be overkill for a vintage trailer. Many big rigs have a generator on board and solar panels, so it can be a complicated system.
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Post by joerolando2701 on Mar 21, 2017 21:34:19 GMT -8
OK so after finding another thread with some great pictures I think I get it.
When there is 110 power to the converter/charger it charges the battery and supplies 12v power to the dc distribution panel when the 110 power is cut the converter basically just dies and power is drawn from the batery. There is no switching mechanism like in 110. Now with a ac/dc converter charger combo I would not be able to tap my inverter into the system with a 110 autoswitch because while it would power all the 110 items it would also kick the dc converter charger on and try to charge the battery with itself thereby draining it just sitting there. But if I'm thinking right if I use a separate dc converter charger and connect it to a breaker in a split panel not connected to the autoswitch then when I switch my inverter on the converter will stay powered down and I'll have 110 from inverter and 12v direct from the battery. Anyone please feel free to chime in and correct me in this I'm mostly guessing here
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Post by joerolando2701 on Mar 21, 2017 21:35:47 GMT -8
Thanks by the way just saw your post
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Post by vikx on Mar 21, 2017 22:14:12 GMT -8
You're welcome.
We try not to get to involved in electrical discussions here. What you are describing is a little over the top for vintage trailers.
I suggest you check out some solar forums and also Off Grid discussions. For a vintage trailer, all you need is a simple small inverter to run low powered 110 items. Anything more and it is not going to work without a battery bank.
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cowcharge
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Post by cowcharge on Apr 7, 2017 17:17:39 GMT -8
Vik's right, running anything off your inverter bigger than a couple of lights and a phone charger takes battery capacity. Watts = amps x volts. So as an example, to power a 60-watt light bulb, it takes .5 amps AC (60w / 120v = .5a). To get that same 60 watts out of your battery it would take 5 amps (60w / 12v = 5a). So for every amp of 120v you generate with your inverter, you need 10 amps of battery power.
Let's say you have one 85 amp-hour Group 27 battery, which is probably the most common size used in small campers. If you want your batteries to last for years you should avoid discharging them below 50%, which means you'd have 42.5 amp-hours of useful capacity in that battery before it needed charging.
Which also means that you'd be able to run that one 5-amp light bulb for only 8.5 hours before the battery needed to be charged (42.5ah / 5a = 8.5h). That's fine if you can charge batteries every day, but if you can't... An LED bulb would help tremendously in that case, as a 60-watt 120v LED bulb only uses about 9 watts of power. 9w / 12v = .75a, which would give you 56.7 hours of use before you needed to charge (42.5ah / .75a = 56.7h). But most other 120v appliances don't have a high-tech, low-draw alternative like LEDs, so you're stuck with much higher draw for say, a coffee maker or microwave. An 800-watt coffee maker would only run for...
800w / 12v = 66.7a.
42.5ah / 66.7a = .64h,
or 38 minutes.
For this discussion, let's assume you have no off-grid charging capability (who wants to run a stinky, loud, most-expensive-in-fuel-per-watt-charging-method-there-is generator?): To start in the right place, start with what you require for electricity. If you start at the other end of the equation with a fixed battery size, then you must modify your lifestyle to live within your battery's means. If your budget/room for batteries/weight limits allow, start with your needs and build the system to suit you, rather than building your life to suit a battery.
To do that, look at the data labels on every appliance you plan to take camping. If they're in watts, just divide by the voltage to get how many amps they draw, and multiply by ten if they are 120v to get the DC battery draw. Then multiply the amps by the amount of time you would use it each day to get the daily amp-hour requirement for each appliance, and add them up. That gives you your daily amp-hour capacity requirement. Double that to get the size of the battery you need to supply each day's usage (50% discharge rule). Then multiply it by the number of days you're going to stay off-grid. It adds up quick.
To continue the 5-amp light bulb example, if you only burn it for three hours a day, it would take 15 amp-hours. So you could use it for almost three days if you used nothing else (42.5ah usable cap. / 15ah per day = 2.8 days). Of course, if you fall asleep with the light on like I do, your battery's gonna be about done in when you wake up.
If some appliances are labeled in watts and some are labeled in amps, to save a little time on the calculating you could calculate the daily usage of watt-labeled appliances in watt-hours and then add them together and divide by 12 to convert to amp-hours all at once instead of one-by-one. But how many appliances can you fit in a tiny camper?
I don't know what you have for a camper, so I have no idea how much space you have. But you can't put too many batteries in a little canned ham without screwing up the tongue weight. I've got 252lbs of golf cart batteries in mine, but it's 22.5' long and has dual axles... As a somewhat PITA option you could carry spare batteries in your tow vehicle if there's room and switch them out when they need charging, just brainstorming for alternatives...
As for wiring the inverter to power the same outlets that the shore power feeds, well that could take some creative wiring, depending on the equipment you have. If your converter-charger also contains the AC distribution panel, feeding it with an inverter might be impossible. Then you'd need a second AC distribution panel for the inverter, what an expensive mess of spaghetti that would be. Or some way to run the 120v from the inverter so that it goes around the converter to the AC panel. I don't know enough about built-in converters to know whether it's possible. I suppose you could always double-wire every outlet back to the two separate supplies (just kidding).
Good luck!
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