Registered Users Posts: 42 ✭✭✭
OK, this may be so basic that I have glossed over the answer somewhere. Here goes. I am always seeing measurements in Amps without any other description. For example, 30 amp fuse, 100 amp shunt, or "it was drawing 6 Amps".

Don't I need to know some more info like volts to know what this really means?

Or am I just trying to always understand things in terms of watts whereas an amp is it's own standalone measurement.

• Solar Expert Posts: 9,358 ✭✭✭✭✭

> an amp is it's own standalone measurement.

Yep. Amps are their own creature.

Watts = Amps * Volts
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• Solar Expert Posts: 5,433 ✭✭✭✭

Amperes (amps) are the measure of electrical current (charge) passing through a conductor (wire) at any given time.

Volts is the amount of electrical "force" moving through a conductor.

Watts (or kilowatts or megawatts etc) is the measure of useable work done. It is measured in relationship to time. For example a 100 watt bulb would use the power of 100 watts. Using that power for 1 hour would be 100 WATT/HOURS (WH)

So to determine the power that any given device uses (or how much power a generating system produces you need to know both the Voltage and the current. So the same 100 watt light bulb, at 120 vac (household voltage) would draw ~.83 amps. A similar light bulb designed to run at 12 volts, would draw 8.3 amps. Thus the measure of POWER, (which is what it ultimately important!) is the product of Volts X Amps = Watts.

Watts are a stand along measure that can have meaning without reference to volts or amps, but amps or volts without reference to the other is fairly meaningless in terms of any useful work that might be done.

Clear as mud?

Tony
• Solar Expert Posts: 27

I have a question about Amps. I have three solar panels and two of them have 3x6 cells they are .55 volts , 3.6 amps & 1.98 watts. The other one is 4x4 cells and has .5 volts 4amps , 2 watts . How do you get it to ware the amps are more theen what they are now. can you tie the panels in to each other by going +,-,
and so on . Right now they are all +++++ &
I'm feeding the charge controler 20 volts and the book on that says it can only take 20 volts.
• Registered Users Posts: 42 ✭✭✭

I think I understand it now. I think I was confused by people listing voltage earlier on in a thread and not repeating it for the discussion at hand.
• Solar Expert Posts: 5,433 ✭✭✭✭

DF,

I'm not sure what it is you are asking.

If you take your 4 panels, wire them in series, plus-minus-plus- minus etc, you will end up you will end up with ~2 volts at about 4 amps. ( assuming each panel is .5 volts/4 amps just to keep the math clean). This would be the best case, not the real world output.

Now if you wire them in parallel,, plus-plus-minus-minus etc you would end up with ~.5 volts at ~ 2 amps. The power out of the system would be the same either way, all things being equal.

Remember the basic equation VoltsXAmps=Watts or Watts/Volts=Amps

So if you double the voltage, you reduce the amperage by 1/2. If you double the amperage you reduce the voltage by 1/2. Think of this example. If you take two AA 1.5 volt flashlight batteries and put them +- you would end up with 3 volts. They would power a 3 volt 1 watt flashlight for say 1 hour. Put the batteries ++/-- you would get 1.5 volts. This would power a 1.5 volt 1 watt flashlight for the same amount of time. No matter how you wire them, you can't get more net power out of them.

Good luck

Icarus
• Solar Expert Posts: 452 ✭✭
icarus wrote: »
... Watts are a stand along measure that can have meaning without reference to volts or amps, but amps or volts without reference to the other is fairly meaningless in terms of any useful work that might be done.

True enough. However, volts or amps without reference to the other is meaningful in other ways. A fuse/breaker is rated in amps without reference to volts. A maximum voltage is often given which, if exceeded, would result in dielectric breakdown. But it is irrelevant to the performance of the device. The same is true for conductors. The gauge determines how much current can safely be carried regardless of voltage. The voltage that a conductor can safely handle is determined by the properties of the insulation (dielectric.)

Craig
• Solar Expert Posts: 5,433 ✭✭✭✭

Craig,

You are right of course. My point is (was) that to say "the light burns 10 amps" or "the light burns 12 volts" means nothing unless it is followed by "at 120 volts" or "at 15 amps" for example.

Tony
• Solar Expert Posts: 452 ✭✭

And, of course, you are right Tony. My post was not a criticism or correction. Just an addition. :-)
• Solar Expert Posts: 452 ✭✭

Mike 870 wrote: »
... I am always seeing measurements in Amps without any other description. For example, 30 amp fuse, 100 amp shunt, or "it was drawing 6 Amps".

Don't I need to know some more info like volts to know what this really means? ...

In the case of fuse & shunt, amps stand alone. "Drawing 6 amps" implies that knowing the voltage (and hence power) would be more informative.

Craig
• Solar Expert Posts: 5,433 ✭✭✭✭

My oh my! The day I can't listen to criticism or correction is the day,,,,.

I may not always be right, but I'm never wrong! LOL!

Tony

PS as so many have learned over the years, if anything my math is more often wrong than right!

T

I am new to Solar PV systems, but I recently installed a cool system in a small barn on my property. I have a 15 watt 15V panel with a charge controller, charging a 102ah deep cycle battery. I am running two 50W 12v light bulbs. Using the formula W/V=A, I guess the draw is around 8amps. I used 12guage romex wire. I actually wired the system as if it were a 12v system (maybe over-kill). However, if I use a 400W inverter to run a tool or appliance...will this draw over 30amps? If so, will the 12g wire be insufficient? How large fuse should I use in the lighting run?
• Solar Expert Posts: 452 ✭✭

Let's see if I can get at this before Tony does.:roll:

If you use the inverter, we need to know how much power will be used by the tools that you have. Not knowing that, and assuming that you intend to use 400W (also not knowing if your inverter is true or modified sine wave) your 12V draw will be ~33 amps. 12ga (solid) is nominal for a 15A 120VAC circuit. So, first answer is NO. Not sufficient. Something more like #8 or #6 depending on the length (round trip) of the cabling.

BTW, a 15W panel is pretty small. Might be enough for your lights, but adding heavy draws to the battery may discharge it far enough for the PV to have difficulty recharging it.

K
• Solar Expert Posts: 5,433 ✭✭✭✭

#12 wire should be OK for ~20 amps. But if you have a very short run you will probably be OK if you fuse it and you loads are of short duration. The biggest issue IMHO is not that you are going to burn the wire up, but more that you are going to have considerable line loss.

In a 12vt system it is pretty easy to figure the current draw. If a tool draws 10 amps running at 120v, it will draw 100 amps from the 12volt source (plus inverter and line losses).

As for you question about what fuse size to use. You should always protect the SMALLEST size wire in the circuit. So if your lighting circuit is #14 wire, a 15 amp fuse would be right. #14 would take a 20 amp.

Having said that, you should protect the inverter wiring by fusing it with the maximum size fuse for the expected load of the inverter. A 400 watt inverter might draw 30+ amp, so you would use wire sized for that (#10 or maybe #*8 bigger is always better to reduce line loss.

Hope this helps,

Tony

PS Kamala is also correct about your panel being pretty small. In general, it is suggested that you have charging capacity of between 5-15% of battery AH capacity, so your 102 ah battery would like between 5-15 amps, or a panel in the 60-100 watt range. As has been mentioned too often before, the quickest way to kill a battery is to chronically undercharge it.