4@12v = 24v

Salvo wrote:
Yeah, that's wishful thinking. In the case of 4 batteries and a 150A 12V load or 75A 24V load, each battery will put out 37.5A, no matter which configuration.

Boy you lost me on that one.

1800w/24v=75a.

4 6v batteries in series will share the load so...

75/4 = 18.75a.

No?

Yeah, that's wishful thinking. In the case of 4 batteries and a 150A 12V load or 75A 24V load, each battery will put out 37.5A, no matter which configuration.

Sal

2oldman wrote:

BFL13 wrote:
No idea what happens with old Peukert!

I would like to think Mr P doesn't affect me as much pumping 1/2 the amps @24v, but that may be just wishful thinking.

The length of time the micro runs should be exactly equal. In each case the micro gets 120V.

Sal

DryCamper11 wrote:

He was commenting on the length of time the microwave runs, not on the change in power loss due to cabling and battery internal resistance. That's roughly the same length of time.

BFL13 wrote:
No idea what happens with old Peukert!

I would like to think Mr P doesn't affect me as much pumping 1/2 the amps @24v, but that may be just wishful thinking.

No, what I meant was how long you could run the MW (for example) with that battery bank in the two situations. A capacity comparison question.

I can do AH capacity and see how Peukert works from all our discussions here wrt 12v battery banks and my own tests of that, but for some reason, can't get it straight for capacity when doing AH and 24v or 48v battery banks.

I was thinking if you halve the amps then you get twice (ignoring Peukert) the time but then you get half the AH in the 24, so it is a wash? So what's the point of going to 24?

But to actually get 24 where you can swap connections to be either 12 or 24 depends on the unit battery size. As seen in the earlier Trojan list, you can do it with 12s but not with 8s so much. If you have to use twice as many batteries to make the 24, then I get lost on apples and oranges, and who is doing what to whom. :( No idea what happens with old Peukert!

A stranger in a strange land.

Salvo wrote:
Well, not quite. If we got a 150A load and 4 batteries each with 15 mohm resistance, the 12V batteries will dissipate 84W, while the 24V batteries will dissipate 21W. There's a factor 4 difference in power dissipation.

DryCamper11 wrote:

Yes. Same batteries, same stored energy, and the MW runs the same length of time (approximately).

He was commenting on the length of time the microwave runs, not on the change in power loss due to cabling and battery internal resistance. That's roughly the same length of time.

I went through the calculations on power dissipated in the cabling, and discussed why that's reduced to a 1/4, and yes, there's also less loss in the batteries, but the power dissipated in cabling and batteries isn't really going to have a huge effect on the length of time that a microwave runs. 150A at 12V (or 75A at 24V) is 1800W.

Even if we use your numbers, the difference is that the energy used to run a MW for 15 minutes with a 24V setup would run the MW 33 seconds less with a 12V setup. That's why I said the run time would be "(approximately)" the same. I don't see that as being a major reason to go with 24 volts over 12 volts.

The efficiency of the inverter is probably more important than the power loss differential due to the current change.

Well, not quite. If we got a 150A load and 4 batteries each with 15 mohm resistance, the 12V batteries will dissipate 84W, while the 24V batteries will dissipate 21W. There's a factor 4 difference in power dissipation.

Sal

DryCamper11 wrote:

Yes. Same batteries, same stored energy, and the MW runs the same length of time (approximately).

BFL13 wrote:
Now if the two 12s were in series for a 24v bank of 150AH, and you had a 24v inverter, the inverter would draw 75a ??? but you can't run the MW any longer than you could with the 12v set-up????

Yes. Same batteries, same stored energy, and the MW runs the same length of time (approximately).

So it is just about wiring? How is it any easier on the batteries with the 24v version?

The wiring is one issue. The current is less, and power lost in the wiring is proportional to current squared, so half the current in the same wire wastes one quarter the power. Not that power loss in cabling is usually a prime concern. As to easier on the batteries, there's lots of info about the difference between series charging/discharging vs parallel charging/discharging, and in general, it's easier to charge/discharge series connected batteries without damage than parallel connected batteries.

mena661 wrote:

BFL13 wrote:
I bet this is to do with those nasty watts things again :(

Yes, the watts thing. :) Amp hours is still the important measure here so go with that. IMO, the benefit of high volts is skinny wires (and access to larger inverters) and the use of cheap PWM controllers on 24V solar panels.

A 150Ah, 48V battery bank has the same storage capacity as a 12V, 600Ah bank (using the T1275's as an example). Watts.

I am having all kinds of trouble with AH and the higher voltages :(

If the 12v inverter draws 150a with the MW on a 12v 300AH battery bank (the two 12s in parallel), we know how that works.

Now if the two 12s were in series for a 24v bank of 150AH, and you had a 24v inverter, the inverter would draw 75a ??? but you can't run the MW any longer than you could with the 12v set-up????

So it is just about wiring? How is it any easier on the batteries with the 24v version?

BFL13 wrote:
Also I am not sure you are better off with 24v batts and a 24v panel than you were with a 12v batt and a 12v panel.

I don't think it makes much difference, except for the wiring. That said, if your system components are heating up, then you're losing power.