Voltage inverters

[James Morse]

I want to have AC current available, probably not a lot of watts.

I have DieHard Silver battery, it's 590 cold cranking and 100 reserve. Does that mean that, say I have an inverter, and run the batter "dead", that it still has 100 to start the vehicle? I'm confused.

And it doesn't tell me how many amp-hours it has, is there any way to tell? If I knew that, then I'd know how much I can run stuff (with the truck not running) before it's a problem.

I could carry spare battery... but... yuck.

Also, some of the small inverters go into the 12V Aux, larger, they have to be wired in. Would you wire it right to the battery then into the cab, or what? Would you run it thru the fuse box?

For instance, a 30" tv takes about 60 watts. That's not much. If you ran it for an hour, you'd use about .5 amp-hours (of 120V current). I have no idea what that translates to in use of DC current.

You can get them all the way from 25 bucks, which might even be enough for me (hooks into 12V Aux) way up to multiple kilowatts, way beyond what I need. I might want something like 400 watts or so, if I'm doing it, I don't want to necessarily get the minimum.

Sure would appreciate any help. Thanks.

 

[RonD]

General rule of thumb for car batteries which are rated in Cold Cranking Amps(CCR) is CCR X 0.7amps = Amp/Hours

So 590 x 0.7 = 413 A/H

But here's the thing about car batteries an WHY they are rated in CCR and not A/H, they are designed with thin plates so they can release ALOT of amps quickly and then be recharged quickly, starter motors need 60-75amps to turn the engine over
These types of Batteries are not designed to be used for long term power, i.e. a slow steady drain

The battery in a vehicle is used to start the engine and then alternator takes over, and ALL electrical power comes from alternator, at minimum voltage of 13.5v
Battery is only 12.8v so with engine running voltage flows TO the battery all the time
So battery is designed for that type of use
If you drain this type of battery down long term it will shorten its life, and you for sure don't want to drain it down to under 9volts remaining
So if you decide to do this then also get a Digital Voltage meter with on off switch, so you can monitor battery voltage while inverter is active


Deep Cycle Batteries are designed to be used long term, thick plates, they can be used to start engines, just not that good at releasing high amps quickly
But they don't mind being drained down under 6volts
These are used in RVs and Marine applications, usually as a second battery not to start engine, but can if not discharged too much


Watts is a relation between amps and volts, calculator here: https://www.rapidtables.com/calc/electric/watt-volt-amp-calculator.html
Just enter 2 known numbers, like watts and volts, then "calculate", and it will show Amps

60watts at 120v = 0.5amp
60watts at 12v = 5amps

So TV would use 5amps per hour from 12v battery

400watts at 12v = 33.3amps per hour from a 12v battery

Watts rating of a device doesn't change with Volts, watts is the "power" it needs to operate regardless of the voltage provided
But the lower the voltage the higher the amps will be

That's why the rest of the world use use 220vAC, only need 1/2 the amps of 110vAC so smaller/cheaper wires can be used

Yes, you would need to run wires large enough to do 40amps to a 400watt inverter, and also install a 50amp fuse at the battery connection for that wiring

Some install the inverter in the engine bay so the larger 40amp wires are short, and then run the less expensive 110vAC "extension cord" into the cab or where ever you want the 110vAC power

 

[James Morse]

Awesome. Thanks so much. It sounds like perhaps a good idea would be to get a deep cycle batter, have it separate from truck, and charge it on the trickle charger, when it runs out, it runs out. No harm to truck.

I still don't get what is "reserve"? Maybe doesn't matter to me, just curious.

At least it opens up possibilities. I really like doing little stuff like that, after the basics are set. Many thanks.

 

[Dirtman]

You can get an optima yellow top battery, they are sort of a hybrid between a regular cranking battery and a deep cycle. But A. They aren't cheap, and B. I still would not power a ton of stuff with the engine off if you only have 1 battery...

 

[James Morse]

Thanks, I definitely agree with your advice.

 

[RonD]

Car Batteries RC, reserve capacity, is an estimated time it can run all electrics in a vehicle if alternator should fail
So its really not an exact time, lol
At night you would have head lights on
Maybe that new 500watt sound system
Cold or hot out so Fan at high

But generally they will have a 1 to 2 hour RC

 

[James Morse]

Ah that's kind of cool, thanks. We used to have cars battery dead and it'd be like "don't turn it off!" Had to park on a down hill to start it or get a bunch of people to push it then pop the clutch usually in second. Maybe you've been there.

But then we also used to drive cars with shot clutches and you'd pick somebody up with the door open and them running alongside, lol, could't take it out of gear and get back in first at a stop, and had to match rpm to shift, best you could.

Those sure were the good old days!

 

[RonD]

Ah that's kind of cool, thanks. We used to have cars battery dead and it'd be like "don't turn it off!" Had to park on a down hill to start it or get a bunch of people to push it then pop the clutch usually in second. Maybe you've been there.

But then we also used to drive cars with shot clutches and you'd pick somebody up with the door open and them running alongside, lol, could't take it out of gear and get back in first at a stop, and had to match rpm to shift, best you could.

Those sure were the good old days!

Yes, I went to High School

 

[James Morse]

https://www.batterystuff.com/kb/tools/calculator-sizing-a-battery-to-a-load.html

It's another calculator to size the battery to the load for a given number of hours.

I don't quite understand why you put in the hours of use but then it says they calculate at a 20 hour rate, so I'm clearly missing something there.

If I'm reading it right, for a draw of 8 amps (tv is .8 amp at 120V so I figure 8 amps at 12V) it says if I run it an hour, is uses 38 amp hours from my battery. So that should be not a lot of discharge... right? And the other calculator says it would use 96 watts at 12V, so a small inverter, say 150W, that can plug into the 12V Aux on the dash, should work fine. Not what I want long term, but just to run the tv, it should work. Please let me know if I'm on track here or not.

Thanks.

 

[Curious Hound]

Yes. 8 amps X 12volts = 96 watts

8amps X 1hour should equal 8 amp-hours.

One thing to remember is that the inverter will have internal losses that use power. So always get a slightly larger inverter than the load you will power. Also, just because you connect a 400watt inverter, doesn't mean it always uses 400watts. It will only use enough power to supply your 96watt load plugs a bit for it's internal losses, maybe 110 -125 watts. The cheaper quality inverter will have greater losses. It is less efficient than one with higher quality design.