Amperage, Voltage and wattage...

[chadster1]

I am helping to set up a float for the Christmas parade in our town. My wife teaches first grade and we are going to have her first grade class on my trailer for the parade.

I am wanting to run some rope lights on the trailer with a chasing effect. I think I got the power requirements figured out but I wanted to post some numbers in here just to make sure I am not missing anything.

150ft of rope light * 5.5 watts per foot = 825 watts

I have a 1250 watt inverter

I have run a 4 gauge power wire from the battery to the back of the truck. The power wire kit came with a 100 amp fuse.

12 volts x 100amps = 1200 watts.

I dont know what efficiency that the inverter has but I would think that I have enough power at the back of the truck to run the inverter that will power the lights.

Length of power wire from front to back, 20ft
Length of Ground wire, 3ft

Anybody have any experience doing something like this. I know this will put a strain on the charging system of my truck but I would think it should handle it for the parade.

Once the lights actually arrive, I will hook them up and do some testing before the parade. I can always add a second battery in the bed of the truck where the inverter is if it draws the voltage too far down on the truck.

I will be pulling the trailer with my 2008 Dodge Ram 1500. It has the towing package so it I think it has a 165 amp alternator.

Any thoughts or suggestions?

 

[Teken]

The second battery will only allow you to operate the lights with a longer run time with the vehicle off. Once the vehicle is running, the second battery will simply look like another load to the alternator.

The 165 amp alternator will be fine to power up the lights. If you decide to install the second battery please do install a battery isolation kit to protect the SLI battery so you can at least start the vehicle.

Teken

 

[chickenhauler]

It really looks like you'll be good to go. As long as your battery is in good shape (and being a 08, I don't see why it wouldn't be), you shouldn't have any issues at all. Out of curiosity, why not go with a 12 volt dc rope light?

 

[chadster1]

The second battery will only allow you to operate the lights with a longer run time with the vehicle off. Once the vehicle is running, the second battery will simply look like another load to the alternator.

The 165 amp alternator will be fine to power up the lights. If you decide to install the second battery please do install a battery isolation kit to protect the SLI battery so you can at least start the vehicle.

Teken

This will only be somehting that is run with the vehicle running. After the parade, the inverter will be removed and the power wire will be disconnected from the battery for safety.

 

[chadster1]

It really looks like you'll be good to go. As long as your battery is in good shape (and being a 08, I don't see why it wouldn't be), you shouldn't have any issues at all. Out of curiosity, why not go with a 12 volt dc rope light?

12 volt rope lights are LED. Very few LED rope lights offer the chasing effect. LED rope lights are at least twice as expensive as regular rope light. I already had the inverter.

 

[79firebird]

If i was you i would add a 2ed battery main reason is draw as well as think about it truck is running so it also needs power lights tail trailer brakes if it uses them etc

 

[Teken]

If i was you i would add a 2ed battery main reason is draw as well as think about it truck is running so it also needs power lights tail trailer brakes if it uses them etc

Once the vehicle has started the battery plays no role. The alternator / generator is the only thing that provides current to the accessories and to keep the vehicle running.

A secondary battery only allows the user to have more *off time* running when the vehicle is not operating.

 

[theoldwizard1]

Length of power wire from front to back, 20ft
Length of Ground wire, 3ft

You fell into the trap everyone else does !

For calculating DC voltage drop, you need the "round trip" length which is twice the distance or 40'. Of course, the steel frame has higher resistance than copper wire so I would call it 50'

Using this voltage drop calculator, you are going to loose 2.4 volts. So if you are starting with 12V, you will only have 9.6v at the inverter, probably not enough.

You need some combination of the following.

• Use less low voltage wire (put the inverter in the cab, run standard extension cord from there)
• Use copper wire on both positive and negative
• Use heavier wire.

 

[Rockbiter]

what about hooking up a little gas powered generator. Some of the little ones are very quiet.

 

[sberry]

Why run a heavy lead? Put the inverter under the hood, run a 25 ft extension cord. whoops, I see the obvious has been mentioned.

 

[chadster1]

what about hooking up a little gas powered generator. Some of the little ones are very quiet.

I already had the inverter. If I need to, I can borrow the 1500 watt inverter that is in my tooltruck.

Why run a heavy lead? Put the inverter under the hood, run a 25 ft extension cord. whoops, I see the obvious has been mentioned.

There is not an feasible place to mount it under the hood. A 1250 watt inverter is pretty big.

I looked up the specs on the inverter and it shows a greater then 90% efficiency.

The parade is not until December 10th so if I need to relocate the inverter to the cab, I have time.

 

[smalltruck]

The voltage drop on the 110 volt line is less than the DC line but You will be happier running a generator. If you have the lights on for an hour you will have a large load on the alternator for that entire time. That will really shorten the life of that unit. Here I can rent a honda inverter generator for 30 bucks a day. Those things are almost dead silent and that would be cheaper than rewiring the truck or a new alternator in 6 months

 

[2LTim]

Chad:
You will not get the 2.4 volt drop using the frame as a ground path, as long as you add an extra 2 guage ground strap from the engine to the frame. Also, cars and trucks run a "12 VOLT" electrical system, but if your alternator is working properly, you should get 14 to 14.5 volts to your battery and electrical system. Adding this value to your calc. gets you 1400+ watts, more than ample for your 1250 watt inverter.
I have 2 - 175 amp forklift battery connectors on my truck to run my winch. One in the grill, and one in the back of the bed. The back one uses the truck frame for the ground with no power loss.
If you neglect to add the heavier ground (Engine to frame) you will most likely get a little whisp of smoke out of the factory ground straps. Then you will spend a lot of time trying to figure out why your lights on your truck aren't as bright as they used to be.
Hope this helps,
Tim

 

[2LTim]

P.S.
Your inverter does not draw 100 amps all the time, only at maximum load. If the numbers you used earlier are close, your draw will only be around 50 amps. This should be a walk in the park for your '08 Dodge. Go for it.
Tim

 

[larry_g]

I would also check that the current draw on the rope light in the 'chase' mode versus 'all on' mode as in chase mode all lamps are not on all the time. If the load you quoted is for chase mode then ignore above.

lg
no neat sig line

 

[chadster1]

I would also check that the current draw on the rope light in the 'chase' mode versus 'all on' mode as in chase mode all lamps are not on all the time. If the load you quoted is for chase mode then ignore above.

lg
no neat sig line

The specs on the rope light just state 5.5 watts per foot. So you do have a valid point that chase mode will use draw less current.

2LTim,

Thanks for the tip about the extra ground strap. I was aware that the actual voltage that I will be dealing with is around 14 volts. I was trying to be conservative. In my experience, its better to have a margin of error than to have compenents running at the maximum rated output.

 

[ForceFed70]

Sounds like you have things under control BUT:

It's been mentioned already, but if at all possible keep the inverter near the battery and use 120VAC extension cords instead. 120VAC extension cords are cheaper than 4ga wire, and you'll have a more efficient system due to less voltage drop.

1.2V of voltage drop on the 12V side = 10% loss
1.2V of voltage drop on the 120V side = 1% loss

Or, think about borrowing a small generator and just put it on the float.

 

[sberry]

For a parade I would be tempted to stick the thing under the hood with a bungee cord somewhere, I have a setup more permanent in nature, would have liked to keep it under hood but wasn't a good idea for long term or for turn on/off, etc. There is usually a couple more things piled in.
I have a master switch and added an outlet to front of truck with gfci, I don't keep anything plugged in to inverter unless I need it which is fairly rare due to battery drills, etc and I didn't want plugs riding in outlets all the time.
Yes, run ground lead to the unit direct from battery.

 

[theoldwizard1]

sberry - Done right !

I love the weatherproof box/outlet on the front !

Is that a modified sine-wave inverter ? How many watts ? What is the typical use ?

 

[Charles (in GA)]

I don't see an issue with loading a 165 amp alternator with 100 amps or so, EXCEPT that in a parade, the motor will be idling or nearly so, and I'm not sure the alternator will produce properly at idle with that kind of load on it.

Charles

 

[theoldwizard1]

I don't see an issue with loading a 165 amp alternator with 100 amps or so, EXCEPT that in a parade, the motor will be idling or nearly so, and I'm not sure the alternator will produce properly at idle with that kind of load on it.

The PCM on most (all?) modern vehicles monitors battery voltage and if it is low will raise the idle speed.

 

[sberry]

sberry - Done right !

I love the weatherproof box/outlet on the front !

Is that a modified sine-wave inverter ? How many watts ? What is the typical use ?

Main reason I had it was to run grinder and drill but battery drills have taken a lot of use from it. I think its modified sine,m don;t recall now, had it for years and it was a Coleman or sumthin, cheap, 2-4k about 150$ or so?. I used it the other day, went to start a sump pump and thought something was wrong, ran a cord from the neighbors and come to find out the pump was seized. I have ran 1/2 hp motor with it.
I put heavier alt on my truck, mostly for plow.

 

[chadster1]

For a parade I would be tempted to stick the thing under the hood with a bungee cord somewhere, I have a setup more permanent in nature, would have liked to keep it under hood but wasn't a good idea for long term or for turn on/off, etc. There is usually a couple more things piled in.
I have a master switch and added an outlet to front of truck with gfci, I don't keep anything plugged in to inverter unless I need it which is fairly rare due to battery drills, etc and I didn't want plugs riding in outlets all the time.
Yes, run ground lead to the unit direct from battery.

Do you have a fuse or a circuit breaker on the power wire underneath the hood before it enters the cab?

The lights will be here this week I hope. I will be able to test the system under a load. I will be able to take voltage readings and temperature readings at various points.

 

[theoldwizard1]

Do you have a fuse or a circuit breaker on the power wire underneath the hood before it enters the cab?

You are crazy if you don't !

A short with that kind of current can create massive amounts of heat !

 

[chadster1]

The lights have arrived. As I am typing this I have them turned on in non-chase mode (all lights are lit) with the truck running at idle. I took some voltage readings that might interest some people.

Truck running, inverter on but lights off (no load on inverter)

Battery of truck = 14.6 volts
At the inverter = 14.6 volts

No surprise here since there was no load on the inverter.

Truck running, inverter on, light on in non chase mode.

Battery = 14.2 volts
inverter = 13.6 volts

With the lights on in non chase mode they are drawing the most amount of current. 825 watts according to the mfg of the lights. There is only a drop of .6 volts from the front to the back, not the 2.4 volts that someone had stated. It is also apparent to me that the charging system on my truck can easily handle the load.

As I stated in my original post, I am running a 20 foot 4 gauge power wire from the battery to the bed of the truck with a 100 amp fuse. I used a 3 foot 4 gauge ground wire to the frame of the truck. I have a 1250 watt inverter.

Now that I know the lights will work, I just need to install them on the trailer/float.

Battery connection

Inverter in back of truck

Voltmeter on dash when lights are on

 

[sberry]

No, no fuse in this line but I did put disconnect before the unit which is always off unless its being used. Now,,, you could take half that 4 and put the unit at the front of the box vs the rear which would help a lot and I wouldn't ground this to the frame, run the other half of the 4 back to the battery. At the minimum take a piece of the 4 and run from battery to frame, the ground bonds from frame to engine etc are not designed to carry large current, just like there is a ground going to engine for starter circuit. No point in burning up wiring harness etc, you don't know where this current will find its return to the battery, heck new trucks even have grounds wired in the loom for lights, small jumper to frame, most of the time from body or engine.

 

[chadster1]

We won first place.

We ended up running the lights and music for about 3 hours. 2 hours in the staging area and the parade lasted about an hour. Everything worked flawlessly!

 

[Charles (in GA)]

Thats a real crew of "puppies" you have there!

Charles