Campinfan wrote:
The reason why I say four of either is because I would have room for 4. That is why I have the question of 4 12 volts which would give me 4 times the amps of one....or 4 6 volts which would effectively give me 2 12 volts. I hope that clears it up. If all things were even....I would have 4 x 12 volts @100 minutes a piece (just pretending here) so that would give me 400. If each 6 volt was 100, I would only have 200 because I know in series only the volts double not the amps but then they would be partially in series so then I would have the equivalent of 2 12 volt batteries @ 100 a piece for a total of 200. So it seems the 12 volt battery is a better idea until I think about how much lower you can drain the 6 volts.
OK, I see a lot of folks responding are messing up on units and it's causing confusion (ie: someone suggested starting batteries have 3-5times the amp-hours for 30 seconds...which makes no sense).
Voltage:
- By wiring them in series, you add the voltages (ie: 2 batteries at 6v puts out 12v power.
- by wiring them in parallel, the voltage stays the same (ie: 2 bateries a 6v put out 6v power.
Amperage: For house loads, it's all but irrelevant unless running a big inverter. Amperage (typically shown as CCA~Cold Cranking Amps) is usually of concern for starting an engine. No harm in using a starting battery to start a engine but for the same size battery bank, a deep cycle will have fewer CCA.
Amp-Hours: This is a measure of the amp draw times the duration in hours. If you pull 8amps for 10hours ~80 amp-hr. It's important to understand that to use it correctly, you have amp-hr @ X volts.
Watt-Hours: If you are comparing batteries of different voltages, it's often better to convert t watt-hr. Watts = volts *amps. So 12v @ 10amps = 120watts. If you draw that for 10hr, you will use 1,200w-hr.
Once catch is how fast you deplete the battery will impact how many amp-hr (or watt-hr) the battery will put out. This is why 5 minutes cranking a truck engine will kill a 70amp-hr battery. Theoretically, 500amps for 5 minutes will use just over 40amp-hr but the battery likely won't crank the engine anymore. (look up the phuerket effect if you want more details).
So let's take your example of 4 12v Group 27 batteries vs 4 6v golf cart batteries wired for 12v:
- The 12v batteries will have around 90amp-hr each. Since you aren't changing voltage, you can multiply to get the total amp-hr ~ 360amp-hr total.
- The 6v batteries will have around 220amp-hr each but when you merge 2 to get 12v power, the amp-hr stays constant. Since you are combining 2 sets of 2, you wind up with 440amp-hr total (importantly @12v)
440amp-hr is significantly more tan 360amp-hr and hence why the 6v batteries are preferable.
Another way to calculate it is watt-hr:
- 12v @ 90amp-hr * 4 batteries = 4,320w-hr
- 6v @ 220amp-hr * 4 batteries - 5,280w-hr
You also get a little boost from the phuerket effect mentioned above as you are drawing at a slower rate (relative to the battery bank size) with the 6v.
Someone suggested it's OK to take the bank down to 20%...if you immediately start charging, it's only minor damage but if they will sit at 20% for hours, yes it does degrade the batteries.
PS: Lithium is very deferent in that they are largely unaffected by taking them down as low as 10%. This allows you to get away with a smaller battery bank in terms of amp-hr for the same usage. It does come with some catches in terms of management and proper charging or you can ruin an expensive set of batteries easily...but it's getting better.
