Power/Inverter Question

[kingb]

Hi everyone,

I'm another guy who doesn't know much about electrical stuff.

I have an early 2000s Grandby with a battery that is now 6 years old. I tried to use a 150 watt inverter plugged into one of the camper's 12v outlets (tried both outlets), but the inverter "alarm" sounded and it shut itself off after a few seconds.

So, I bought a 400 watt inverter and tried the same thing - same result. Then, I hooked the 400 watt inverter directly to the battery, and it worked fine (but noisy).

Other things work fine with the camper's 12v outlets (cell phone chargers, small fans, etc.).

Do you think the issue is that the battery is old, or something with the camper wiring not being able to support that power?

Thanks for any advice!

 

[billharr]

Get a meter VOM and check your sockets. Make sure the center is + and the outside -
This may cause the alarm, especially if it work off the battery.

 

[craig333]

I'd guess the original wiring to the outlet isn't up to supplying enough amperage. Those things are power hogs. Mine connects directly to the battery.

 

[esimmers]

I'm with Mr. Mumbles. The original camper wiring is more than adequate for normal loads (lights, water pump, heater fan) that draw only a few amps. That's why the wiring is not sized for large loads.

Roughly speaking, watts = volts X amps. With our 12-volt system wiring a 5-amp draw is pretty darn large (60 watts). Remember, your camper battery's capacity is at best probably only 80-100 amp hours (and you never want to discharge a battery more than 50%). So even a 5-amp draw (60 amps) would run your battery down in 8-10 hours.

Trying to run a 400 watt inverter (35+ amps at full power) on that wiring is like trying to blow peanut butter through a straw: The small camper wiring that's just fine for small loads is overwhelmed; the voltage at the inverter drops, and the inverter's low-voltage alarm goes off.

Remember, even if you follow Mr. Mumbles advice and hook up your inverter with short, larger wiring, you can run your battery down very fast anyway. Inverters are not totally efficient, they use electricity even when nothing's connected to them and AC appliances often draw a lot of juice.

 

[craig333]

Mine has a remote switch so it stays off unless its being used. I use it for very short periods. Maybe three minutes at most running the microwave.

I did find a new use recently. Now it also runs my coffee grinder. Probably could find a twelve volt or even a manual grinder but since I had one and it only runs a few seconds I figure why not.

 

[Casa Escarlata Robles Too]

I use a 150w inverter works for coffee grinder or recharging lap top and such.
It's wired directly to the battery about 6" away.
Only use it a short time and make sure it's turned off when not in use.
Before I went with the larger solar I would only use it while driving for most things.
Now with the 105w system I feel I can use it when in good sun and parked.

Frank

 

[kingb]

Thanks for all the great info. This forum always saves me a lot of time and guesswork!

I think I'll buy another laptop battery - that might be enough to get me by. I'd also like to connect a small inverter directly to the battery. Frank - what 150w inverter do you have? It looks like most of the small ones don't have clamps for connecting to the battery - just the 12v plug.

 

[Beach]

I would have a 6 year old battery load tested. After charging let it sit for a few hrs. so your not reading the "surface charge". Camper wiring should be adequate for minimal amperage items(cell phones comp. etc). You should also ck. old connections, they might be dirty or need tightening.

 

[Casa Escarlata Robles Too]

Thanks for all the great info. This forum always saves me a lot of time and guesswork!

I think I'll buy another laptop battery - that might be enough to get me by. I'd also like to connect a small inverter directly to the battery. Frank - what 150w inverter do you have? It looks like most of the small ones don't have clamps for connecting to the battery - just the 12v plug.

Not sure of the brand. A friend gave it to me. He got it with some Harbor Freight solar panels.
I just mounted it first with some Velcro but that kept coming off so I just used an aluminum strap.
It's about 6" from the battery and seems to not be in a place that gets in the way.
I wired it directly to the battery.
Frank