bf_ups-inv

An Inexpensive Approach to “Inverting” Your Trailer

Here is one of those solutions looking for a problem. I've got an old Uninterruptable Power Supply that failed during one of our power outages last winter. Curious as to where the problem lay ( bad battery, bad inverter or charger section) I pulled the small 12 volt inverter battery, rigged up a cigarette lighter plug clipped to the battery leads (see the picture), went out to the trailer and plugged it in. Using a 100 watt light for a load, I switched it on. Bingo, worked fine. Hmmm, dead battery, good inverter. After confirming that the battery would no longer accept a charge, I got to thinking. I don't need an inverter since I already have one. But why wouldn't this make a nice unit for a small trailer that didn't need or want some mega power inverter system?

So, from here on, this is sort of a "what if" project. I don't see why it wouldn't work but I've only experimented. Nothing "official". Food for thought.

Maybe yes, maybe no.

There's a couple of caveats: First, the electronics in these things do just fine on an intermittent basis. Whether they are robust enough to power a TV off and on for many weeks, I don't know. But if you have an orphan UPS box with a dead battery and don't care to restore it ... what the heck.

Second, you must use this like you would any simple, stand alone, inverter. Do not try to wire this into your trailer's 120 VAC system!!! Plug any small appliance you might have directly into the rear of the UPS. If you attempt to integrate something like this into your trailer's AC system, you must have a lock-out system that prevents shore power from reaching the inverter output. If you don't, you likely will make sparks and possibly some fire. (If you want that kind of system, you'd be better off moving to higher end equipment, like a Xantek inverter/charger.) For that reason, you need to cut the 120 VAC cord coming out the back and cap off the individual wires. Even better would be to get inside the inverter section and disconnect the AC power cord completely.

Nothing-fancy Tripp-Lite UPS. It's several years old now but, with a 12 volt power source it still works fine. This one puts out only 285 watts, continuous, but can surge momentarily to somewhat higher. One bonus is that these are designed to provide backup power for computers and peripherals. That answers one important question about its compatibility with these systems, in case that's what you want to power in your trailer. The ones you find in the automotive or hardware store inverter might be fine for shavers and TVs, not so much for your laptop.
Here's a view from behind. In this UPS, the battery pack slides into a large slot in the bottom. The battery is a sealed unit so isn't servicable itself. New ones can be purchased off the internet for various amounts. A replacement for this unit would cost about $35. I likely will do that, since it's cheaper than buying a whole new UPS. One question that might affect whether you try to refurbish your UPS with a new battery is this: Suppose it's the battery charging circuit that's at fault?
Here's a closeup of the rear. This is what I would do: 1. Get rid of the AC power cord (per the caution, above). It might be tempting to plug this into a receptacle believing that, when hooked up to shore power, the internal charger will charge your house battery. It might, but it would take a very, very long time. Remember, this is a very low capacity charger/maintainer designed for the sealed battery that normally resides inside the unit. Keep things simple: cut the cord and charge your house battery with a higher capacity (faster) charger designed for that function. 2. Hook the battery to the leads shown here. Red is positive. Use wire heavy enough to carry the load (See below). Set the front switch(es), and you have instant AC at the receptacles on the back.
Electrical stuff can be risky if you don't know what you're doing. The usual disclaimers apply: I'm not responsible for what you might do with this information or happen to you or your property if you mess up. Or even if you don't . ;-)

Nothing-fancy Tripp-Lite UPS. It's several years old now but, with a 12 volt power source it still works fine. This one puts out only 285 watts, continuous, but can surge momentarily to somewhat higher.

One bonus is that these are designed to provide backup power for computers and peripherals. That answers one important question about its compatibility with these systems, in case that's what you want to power in your trailer. The ones you find in the automotive or hardware store inverter might be fine for shavers and TVs, not so much for your laptop.

Here's a view from behind. In this UPS, the battery pack slides into a large slot in the bottom. The battery is a sealed unit so isn't servicable itself. New ones can be purchased off the internet for various amounts. A replacement for this unit would cost about $35. I likely will do that, since it's cheaper than buying a whole new UPS.

One question that might affect whether you try to refurbish your UPS with a new battery is this: Suppose it's the battery charging circuit that's at fault?

Here's a closeup of the rear. This is what I would do:

1. Get rid of the AC power cord (per the caution, above). It might be tempting to plug this into a receptacle believing that, when hooked up to shore power, the internal charger will charge your house battery. It might, but it would take a very, very long time. Remember, this is a very low capacity charger/maintainer designed for the sealed battery that normally resides inside the unit. Keep things simple: cut the cord and charge your house battery with a higher capacity (faster) charger designed for that function.

2. Hook the battery to the leads shown here. Red is positive. Use wire heavy enough to carry the load (See below). Set the front switch(es), and you have instant AC at the receptacles on the back.

Electrical stuff can be risky if you don't know what you're doing. The usual disclaimers apply: I'm not responsible for what you might do with this information or happen to you or your property if you mess up. Or even if you don't . ;-)