Electrician Talk banner
1 - 9 of 9 Posts

·
Registered
Joined
·
20 Posts
Discussion Starter · #1 ·
I'm working on a film set right now and we did a set up where we tried to power a couple lights off a deep cycle marine battery. I'm more accustomed to using AC generators and admittedly don't know much about DC power systems/batteries, and I've run into some trouble that i'm trying to figure out. Initially we tried to power two tungsten 1k lights off a 3000w inverter wired directly into the picture car battery with the engine running. It didn't work at all, the inverter started beeping and the lights started to flicker. My theory is the voltage on the car battery dropped substantially under 12v causing the electronics in the inverter to suffer and the lights to flicker. But I really thought with the engine running it would work - too much of a load for a car battery even with the engine running? So I called a battery store and talked to their expert, he assured us if we got two deep cycle marine batteries and wired them together in parallel to boost the amperage they should power the two lights for quite a while. So we picked up two Everstart 122 amp-hour batteries, paralleled them, and hooked them up to the inverter/lights. This worked for about 15 minutes, then the lights went out. We charged the batteries and tried again, this time I think we got 5 minutes before the beeping and flickering started. So they didn't have the reserves to go for very long, and they didn't seem to hold their charge as well the second time around despite what the battery expert told us. So I'm just curious why none of this worked. Is 2000w just too much load for a couple of batteries even if they are big deep cycle marines? Were we shafted by a battery salesman into buying a couple non-returnable batteries? Our next plan is to step everything down a bit - this time it will be 2x 400w LEDs with a 1000w inverter, hopefully this time hooked up directly to the car battery if it works this time... any thoughts on how much success we might have with this?
 

·
Registered
Joined
·
4,154 Posts
First I am not familiar with the discharge caricaturists of a Marine battery, BUT all batteries are designed with a different load in mind. for long duration discharges a Telco or UPS battery is best.

Second no battery (unless you go with multiples and I mean multiples) of a Telco or UPS battery is going to give you a long discharge period, you state a 3000 watt inverter what is the load? I'd bet the inverter is about 65-75% efficient. So you have those losses.

The recharge time for your battery to 100% is typically 24 hours (the last percentage of charge takes a while the majority would be in the first few hours.

Each deep discharge will take some life from the battery and every battery has only so many deep cycle discharges.

What you would like to do is a tough nut to crack, why not a generator?

If you gave the load and duration I could provide some suggestions and those battery guys typically aren't experts. They are knowledgeable but not experts
 

·
Registered
Joined
·
20 Posts
Discussion Starter · #3 ·
The load is two 1k lights, so 2k out of a 3k inverter. It would need to go for about an hour - not necessarily a continuous hour, we would turn it off between takes but about that. I'm not familiar with telco or ups batteries, are those a brand or a different type of battery all together? What can you tell me about them? How many multiples do you reckon we'd need to handle that load? It doesn't really matter anymore, we're going with lower watt LED fixtures and a smaller inverter, these questions are just to satiate my own curiosity at this point. We can't do a generator because this is on a car for a film and the car is moving, the genny would have to be rigged to the car and there's nowhere we can put it where it won't be a nightmare for sound. They make special devices for exactly this sort of thing for film productions, but that gear is expensive and this is a low-budget production we we're making due with what we can. Those two 1k par cans were the best possible thing stylistically because they look just like car headlights except they're way brighter, but seems we can't find a way to use them with the power system we have so we'll just go with what we can to get proper exposure. Thanks for the reply.
 

·
Registered
Joined
·
4,154 Posts
I should have added that long duration (above 15 minutes) to a deep discharge of 1.67 can be permanently damaging to the battery and you if you want to get a long life you should consider a higher low voltage shut off, like 1.75 or 1.80 or higher per cell.

This increases the number of batteries you need to obtain the discharge duration.
 

·
Donuts > Fried Eggs
Joined
·
17,042 Posts
The problem with Ah ratings is that they're based on a specific discharge rate-over-time. A 122Ah battery doesn't necessarily mean it will supply 122 amps for an hour unless it was actually designed for that.

I don't know much about marine batteries, but it looks like they are based on a 20 hour rate. So that means a 122Ah battery is designed to supply a 6.1A load for 20 hours.

You try and get full Ah current out of it in an hour, and that capacity drops off considerably.
 

·
Registered
Joined
·
2,969 Posts
If you got 15 mins from two batteries, then for one hour you need 8 x batteries.
But thats 100% discharge, which is never a good thing for a battery,
50% is more reasonable, so your really need minimum of 16 x batteries.

Still think it's a good idea ?
Possible, but impractible.
 

·
Registered
Joined
·
5,652 Posts
It's much more likely that the immediate problem here is that they are tungsten lamps and the cold inrush current of the tungsten is overloading your inverter, activating it's crowbar circuit to protect itself. Tungsten has what is called a high positive temperature coefficient of resistance, which means that the higher the temperature, the higher the resistance so conversely, the lower the temperature, the lower the resistance. So until they get white hot, they are very low resistance and often look like a short circuit to things like an inverter protection scheme.

If you can, put a dimmer on the lights and start them up slowly, they will probably work fine. And old fashioned wire would resistor type would be best because some electronic dimmers will not like being fed from an inverter, but they are getting hard to find now.

As to how LONG they can run on the batteries, that's another issue.
 
  • Like
Reactions: Fredman
1 - 9 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top