Confused

System

Ok here it goes. I will try to keep my question short, but feel free to make your answers as long as you want. I have been thinking about this for 2 days, maybe I'm just not grasping the obvious.

If I (for example and ease of math) have 6, 12 volt batteries @100 AH each and I wire them in parallel I end up with:

12 V dc @ 600 amp hours. Right so far?

Now if I take those same batteries and I wire them in series I end up with,

72 v dc @ 100 amp hours. I lost my storage capabilities right?

But here is where I get confused.
12 v x 600 ah = 7200 watt hours OR 72 v x 100 ah = 7200 watts hours
Its the same. So is my power storage the same? Or did I loose my storage by wiring in series.

Why would I want to wire my batteries in series?

I have a couple more, I will post them separately.

niel

Re: Confused

your calculations are correct and you lost nothing and gained nothing as watts equals watts. it is the same either way and is just a matter of preference for the circumstances at the time as to how it's wired.

adding here you can ask your other questions here.

BB.

Re: Confused

Choosing a voltage for your battery bank does get a bit more complex...

12 volts is popular because lots of 12 volt car/boat appliances/adapters/inverters are out there.

48 volts (and to a lesser degree 24 volts) are popular for larger systems... Because P=I*V, if you raise the voltage by 4x, you cut the current to 1/4. Example:

4,800 watt inverter (well pump, run much of your home). Assume 80% inverter efficiency

4,800 watt * 1/80% * 1/12 volts = 500 amps
4,800 watt * 1/80% * 1/48 volts = 125 amps

It is much easier, cheaper (and to a degree safer) to wire for 125 amps vs 500 amps...

Also, you will not find many "home/small commercial" systems with DC voltages above 60 VDC... Above 60 VDC, the circuits are considered to be "dangerous" and must be treated like 120 VAC (no open terminals on batteries and such).

Also, DC in general has some other special hazards.

1. DC arcs are sustained much better than AC. Switches/breakers/fuses must be designed for DC (much larger than the equivalent AC devices).
2. DC causes our muscles to contract--so if you get a shock, you cannot let go... Unlike AC which typically just knocks you on your rear end.

In general, there are no right or wrong answers in how you design your system--just what is available and cost effective for your specific needs.

And as Niel said, you can keep adding your questions to this thread... You don't need to open a new thread for each question.

-Bill

System2

Re: Confused

Thanks for your time guys.

So in my example I did not loose the amps in series?

Your answers lead into my next set of questions. If you wire my example in parallel, is there a higher risk of shock due to the amp potential? or is it higher in series or is it the same either way?
I'm still confused on the watt hours vs the amp hours thing......
Are wh and amp hours basically the same thing for sizing?
With AC a good set of buckskin gloves will help you not to get zapped. Is this true for DC?

Example 2
If I were to install 5 solar panel, each @ 130 watts, 17.6 v, 7.39 amps:
Parallel = 17.6 v, 36.95 amps, 130 watts or would series be a better choice.
In this example I must size the wire for 40 amps. The lower the voltage the more loss will occur right? How do I figure my loss in voltage (is it called voltage drop)?
The higher the voltage the smaller the wire and losses do not effect the overall voltage as much, right or wrong?
Ok enough for this one. My head is going to explode. Thanks again in advance.

mike95490

Re: Confused

Wired in series, for 48V, your 50W light bulb will draw 1A a 12v, 50w bulb draws 4.1A. You are trading volts for amps, but you still get 50W of lighting.

You are also tradeing copper for rubber, and rubber (insulation) is a lot cheaper! 24V insulation is about the same price as 600V insulation, but 50A copper is a lot more than 3 amp copper !

BB.

Re: Confused

Haight wrote: »

Thanks for your time guys.

So in my example I did not loose the amps in series?

You did not loose anything in terms of "power"...

P=V*I

If you double V, and 1/2 I, the multiplication of the two are the same.

12 v x 600 ah = 7200 watt hours
72 v x 100 ah = 7200 watts hours

Both are true, and represent the same amount of work...

Your answers lead into my next set of questions. If you wire my example in parallel, is there a higher risk of shock due to the amp potential? or is it higher in series or is it the same either way?

Shock potential is a combination of voltage and resistance... The higher the voltage, the more likely you are to get shocked. The less the resistance (water, salt water, etc. on your skin, wet cloths, wet shoes), the more likely you are to get shocked.

In general, bare dry/slightly moist skin, 12 volts--you probably will not feel anything. I have gotten mild shocks at 24 volts. And above 60 volts is considered "dangerous" by regulatory/safety agencies.

Current, anything over 0.005 amps (5 milliamps) will give you a good jolt. More than ~0.015-0.060 amps in the proper place (somehow through your heart) and you run the risk of stopping your heart and causing death. In other words, a stack of 100 flashlight batteries has more than enough voltage and current to kill you.

I'm still confused on the watt hours vs the amp hours thing......
Are wh and amp hours basically the same thing for sizing?
With AC a good set of buckskin gloves will help you not to get zapped. Is this true for DC?

Take Amp*Hours and multiply by voltage, and you get Watt*Hours:

Amp*Hour * Battery Voltage = Watt*Hours (P=Watts=Amps*Volts=I*V)

Example 2
If I were to install 5 solar panel, each @ 130 watts, 17.6 v, 7.39 amps:
Parallel = 17.6 v, 36.95 amps, 130 watts or would series be a better choice.
In this example I must size the wire for 40 amps. The lower the voltage the more loss will occur right? How do I figure my loss in voltage (is it called voltage drop)?
The higher the voltage the smaller the wire and losses do not effect the overall voltage as much, right or wrong?

Since you are are talking about a decent sized system (5x130W=650 Watts)--you will probably want a "MPPT" type solar charge controller (Outback MX/FM family is one popular brand. Xantrex, and other also have their versions).

5x17.6volts=88 volts DC @7.39 amps

The MPPT type charge controller will "transform" or "down convert" the 88V@7.39A to:

88V*7.39A / 15 volts (12 volt battery bank) = 43 amps (a bit less due to conversion losses)

Or with parallel solar panels:

17.6V*5*7.39A / 15 volts = 43 amps (same as above--probably closer to 40 amps after losses).

The difference is that the wiring from your solar panels to the charge controller only needs to handle 8 amps vs 37 amps... Using the Voltage Drop Calculator (from this thread):

For example, say it is 50 feet from the solar panels to your charge controller (round trip is 100 feet of wiring). We want 3% maximum loss down the wire. From the spread sheet, we get:

8 awg wire gives 2.5% voltage drop at 7.39 amps (series panels)
2 awg wire gives 3.2% voltage drop at 37 amps (parallel panels)

So, going in series, with an MPPT type solar charge controller, can save you, roughly, 75% of the cost of running the copper wire from the solar panels to the charge controller.

You are also correct in that pure voltage drop, the higher voltage, the more drop your system can withstand...

2 volt drop from a 12 volt battery -- gives you 10 volts--not much will run at 10 volts (10.5 volts is a "dead" 12 volt battery).

2 volt drop from a 48 volt battery, everything will work fine (down to ~42 volts or so).

Ok enough for this one. My head is going to explode. Thanks again in advance.

Just keep asking question and read the FAQ's that are filed under major headings (charge controllers, inverters, batteries, etc.) in Wind-Sun online-store (our host).

-Bill

niel

Re: Confused

i believe the voltage is 50v for the dangerous point and many 48v pv systems will have voltages far in excess of 50v just for the record.

as to amps, i assume you know that is current. amphours or ah is amps in relation to time referenced to 1 hr. if you have a light drawing 1 amp over 5 hours that is 5 amphours. if a light draws 3a for 3hrs and none for 2hrs, this is what? yes, it's a trick question, but it apllies to the time it's drawing so it is still 3ax3hrs=9ah. how about 2a for 1/2 hr? .5hrsx2a=1ah.

the same principle applies to watthours as it's the amphours x the voltage reference to 1hr. we already covered the power aspect as that is volts x amps = watts. the watts is the work for in an open circuit you have the volts and no amps so no power or watts until you have both. to proportionally lose one and gain in the other keeps the power the same. the reasons for going with higher voltages or lower voltages as well as higher or lower amps are different matters of concern as to how that power is affected or utilized.

System2

Re: Confused

Hey THANKS for the help. Your answers helped alot. I had a long day so I didnt get home in time to research my other questions. I will post my layout 2morrow to see what you think. Again Thanks for your time and answers. Hopefully I will be able to help someone out as well in the future.

BB.

Re: Confused

There are several voltages and other issues on what voltages are "dangerous"--depending on which section of code you work under...

411.2 Definition.
Lighting Systems Operating at 30 Volts or Less. A lighting system consisting of an isolating power supply operating at 30 volts (42.4 volts peak) or less, under any load condition, with one or more secondary circuits, each limited to 25 amperes maximum, supplying luminaires (lighting fixtures) and associated equipment identified for the use.
It’s important to note Article 411 applies to listed lighting systems, meaning a product designed for that purpose, not one assembled by the user from various components. While Article 411 may not apply to IRL, the 30 volt or less is an important limitation set by the NEC in general, as below 30 volts AC is generally not considered to be a shock hazard.

Grounding

Safety grounding establishes a low impedance path to the source to remove dangerous voltage due to a ground fault, to prevent shocks and fires. The rules for grounding are covered in NEC Article 250. Section 250.20 lists the AC circuits that are required to be grounded:
250.20 Alternating-Current Circuits and Systems to Be Grounded.

(A) Alternating-Current Circuits of Less Than 50 Volts. Alternating-current circuits of less than 50 volts shall be grounded under any of the following conditions:
(1) Where supplied by transformers, if the transformer supply system exceeds 150 volts to ground
(2) Where supplied by transformers, if the transformer supply system is ungrounded
(3) Where installed as overhead conductors outside of buildings

AC circuits operating below less than 50 volts are not required to be grounded, except as given above in (1), (2) or (3).
In Article 720 Circuits and Equipment Operation at Less Than 50 Volts, Section 720.1, Scope states This article covers installations operation at less than 50 volts, direct current or alternating current. Section 720.10 refers to Article 250 for grounding requirements.
Article 725 does not require grounding for circuits operating at less than 50 volts per Section 250 112.(I). Generally, grounding is not required for circuits operating at less than 50 VAC. There are exceptions, for example: hazardous locations or patient care receptacles. Also, if the IRL lamp circuit was subject to being energized by a higher voltage than grounding may be required. Locations subject to lighting may require grounding.

Shock Hazard

The NEC contains many references to voltages below 30 VAC being considered safe from contact. For example: Article 620 Elevators, Dumbwaiters, Escalators, Moving Walks, Wheelchair Lifts, and Stairway Chair Lifts do not require working clearance for low voltage circuits.
620.5 Working Clearances.

(D) Low Voltage. Uninsulated parts are at a voltage not greater than 30 volts rms, 42 volts peak, or 60 volts dc.

Any voltage can be considered dangerous, given the right conditions, but generally circuits under 30 VAC RMS and 60 VDC are safe, and IRL using these voltages or less may be suitable for direct burial or sawcut applications.

...
Summary-In general:

• Circuits operating at less than 30 VAC rms and 60 VDC have a reduced shock hazard
• Circuits operating at less than 50 VAC or VDC do not require safety grounding.
• Circuits exposed to lighting (run overhead) require safety grounding
• Circuits operated from a supply exceeding 150 volts to ground require safety grounding
• Circuits supplied from an ungrounded supply require safety grounding.
• The usual separation requirements for low voltage conductors apply (low voltage conductors can not occupy the same enclosure, box or raceway with power (120 VAC)
• Conductors even if insulted for the maximum circuit voltage (See FPN to 300.3(C)(1) and Section 90.3)
• The type of power supply, and secondary circuit protection needs to be evaluated. Failure of the power supply could energize the secondary at the input voltage.
• The installer, manufacturer and AHJ will determine the installation requirements. Consideration has to be given to shock hazard, public safety, and maintenance requirements. The most conservative installation would be rigid metal conduit, with a minimum cover depth of 24” per Table 300.5 PVC conduit can be used, but if exposed to physical damage it must be Schedule 80 per the UL Listing. An alternative would be to concrete encase the PVC conduit.

-Bill

niel

Re: Confused

your welcome. when you think of your questions, try to see if they are already addressed here on the forum. hopefully one day you will be helping people here too for sure, but there's much to learn.:cool::D
even for us experts, there's always something we don't know so it's an ongoing process.