Actual pumping rate will be subject to change based on experience after our first few battles. 30gph is pretty light, but we also have little idea how easy it will be to inflict damage. Same thing for different ship classes. Once we have a better feel for how damage works in AOS, we can start changing things.
Exactly my point. Different sizes and type of batteries perform differently under load, therefore the battery makes a difference.
Basically, the internal resistance of the battery matters because you're burning more power in the process of making power. I^2R losses. And the resistance affects voltage out under load because it's a voltage drop in and of itself. If you do a basic circuit and run throught Kirchoff's voltage and current laws, it becomes clear. More to the point, I can't believe that 21 years out of nuclear EM A-school, that I can still spell Kirchoff or remember that he had laws.
So if I have a 6.4V lifePO4 battery and use it with a pump and it draws X amps and used X mAH over a 30 min period.. then I take the SAME pump.. use a 6.0V Nimh Pack .. and get X amps and X AH you are saying the pack with the least resistance will use the least amount of power. Would it even be measurable? I agree with the engineers that if measured to 6 decimal places there is a difference in the usage of the battery but I think the point is, within the usage of this hobby, .5 ah is in the 'ball park' and for all intents and purposes can be considered the 'same'. I have run Nimh and Life and the only reason I ran Life was the increased capacity per Ounce, internal resistance was never a factor. In my testing if my 20ah of Nimh lost 1ah to the pump but the 20ah life battery gave up .5ah...its virtually the same as it will have no effect on my run-time. If for some reason I have chosen a battery that just barely has the AH capacity to handle my ship for a sortie/battle then I would not list that as a battery failure but a design failure. I DID however have to run 4 Lifepo4 cells in order to provide the amount of current needed to run two titan 550 pumps, which 3 Nimh packs couldn't do. I would use 4 Nimh packs but it would be too heavy and wouldn't fit in the ship (.. capacity to weight issue)
And you also missed my point. I said: when COMPARING a pump DESIGN, you measure the voltage and amperage under load to figure the pump wattage, not the no-load battery voltage. Batteries output different voltages at different times and the pump output changes as a result, I get that. Battery internal resistance and resulting voltage sag varies with the chemistry of the battery and the internal discharge state of said battery. But the pump motor at any instant in time only cares about the power available across it's terminals, not what the battery internal resistance is. So when you are characterizing how a pump system performs you need to remove the battery voltage sag from the measurement in order to get usable values. The following numbers are not exact, but I believe they are pretty close. I think it will help to consider the restrictor vs GPM question from a different angle. A Gel Cell at 100% charge and a 1C discharge rate might only have 10% voltage sag, down to 11.4V but at 30% charge it may have 30% sag, down to 8.8V. A 3 cell LiFePO4 setup under the same conditions might show 9V at 100% charge and 8.8V at 30% charge. Case 1: setup a pump for 1.0 GPM and test the GPM at 100% charge, using the above batteries, what happens later when the batteries are mostly used up? With used batteries the Gel Cell pump is pumping around 0.7 GPM, while the LiFePO4 powered pump is outputting .97 GPM. Case 2: Setup the same pump with a restrictor calibrated to 1.0 gpm at the 30% battery charge level where the battery voltages and the power input to the pump are the same between both sets of batteries. (This is a point where the same restrictor size works for both setups) The gel cell pump might output around 1.3 gpm at 100% charge and 1.0 gpm at 30% charge. The LiFePO4 powered pump output would be 1.03 gpm at 100% charge and 1.0 gpm at 30% charge. So did using a GPM limit vs a Restrictor change the relative merits of either battery type? Nope. Gel cells are still heavy, have a shorter lifespan and the power output drops off early, but they are relatively cheap. In which case is the Gel Cell most competitive? With a restrictor. Which situation is better balanced with mostly discharged batteries? The restrictor. Case 3: Add a 4th cell to the LiFePO4, this gives a 33% increase in peak power available, and matches up the two (restrictor pump setup with 100% charged batteries) gpm output level between the two battery types. Output for LiFePO4 powered pump in the GPM setup remains 1.0 and 0.97 gpm. Output in the restrictor setup is 1.4 gpm (12V) and 1.3 gpm @ 30% charge (11.7V) (Compare gel cell in GPM mode is 1.0 and 0.7 gpm, gel cell in restrictor mode is 1.3 gpm and 1.0 gpm) This is where the perceived pumping advantage for LiFePO4 comes from; the higher operating voltage and lower drop-off. If we used 16 volt gel cells people would think gel cells were a better battery than 4 LiFePO4 cells. Again I am of the opinion that the battery type used in a ship has not a lot to do with how much a pump costs, or what motor type you should select (except as needed to match peak voltage level and rpm). Battery selection and charge state do change where the pump operates on it's output curve at any given point in time, but the battery does not change the actual output curve for a pump, which is a graph of Power Input to the Pump vs GPM output from the Pump. Internal resistance of the battery is power wasted in the battery, not part of the Power Input to the Pump. 9V across the motor terminals is 9V, regardless of how much the battery voltage sagged to get down to 9V. If you are sizing your battery correctly (50%+ reserve power to allow for battery aging and such) you should never get into a situation where the battery type or discharge level matters significantly to the pump performance anyway. rcengr you are correct that I was neglecting the performance point of a pump changing over the discharge cycle of a battery with different battery types when I said "Pumps work the same no matter what batteries you put in the boat". The technically correct statement would have been "Pumps work on the same output curve no matter what batteries you put in the boat".
True, it very much is. As long as nobody's getting mad. I'm still not sure about the same number of holes sinking a frigate as a first rate, which gpm seems to do. I don't see any historical accuracy from gpm. Reduced damage/patching, regulated end result, yes. But these ships get only one pump for damage control. At the same limit. Not all ships were equal. Some were better built, or better crewed, or just bigger and badder. I don't see how a system that says a SOL has the same damage control ability as a 20 gun sloop can be good. As to gpm for fast gun, not something I'd get behind. I just dont see an unbalancing effect from pump techniques. Just different design/battling options.
5 gpm out of 1/8" is bovine scat. Or better and to the point I have not seen this pump and I doubt it exists.
+1 to the geek.... I ran that model not long ago using the converging diverging nozzle with 1/8 orifice... you cavitate badly and the pressure required is absurdly high to hit this flow. I looked into legal pump designs that could produce that and you are talking kilowatts of power to drive the pump...
My statement was based on the outlets designer's words, not anything I measured directly. But since the designer tends to test his stuff, 5 gpm was believable. I did see it, and saw it operate. Didn't believe it at first either before seeing how it operated. I was of the mind at the time that 3 gpm was close to our limits without excessively high wattage.
Might the "super pump" be more of a myth than reality? And if the issue is one of cost of the pump system, should we not consider banning solenoids as well? They're pretty pricey too. As to AOS, if the consensus of captains is going the gpm route, is there any possibility of doing differential rates for different classes(rates?) as we see how things go once ships start hitting the water and actually battling? Or allowing more than one pump (trade a pair of guns for a second pump etc)? I ask because I tend to like the idea of a little more spread/flexibility in ship design/damage control vs firepower etc.
Pumps are cheap (less than $100 for the best) and even cheaper to make. "Super Pump" is relative to what you have seen in the past. Sounds like Treaty is more your bag, if you want to make it simpler, cheap and less technical. But much less carnage.
Actually, I prefer more carnage. I want to battle. To me, that's the point of the hobby. I like fast gun how it is. My questions were more geared towards AOS, since it's in the formative stages and I wanted to know the rationale behind going with a gpm system, of which I am not particularly inclined to think is either realistic or fun.
I'm not sure how a restrictor arrangement improves this. I do however see (and somewhat agree with) the argument for different classes having different GPM targets.
More variation. It seems to me that a restrictor system allows a bigger range than a gpm, because a captain can choose to put more pep in the system if he wants to give up room to more battery power or less endurance on the water. I could be totally wrong, as I have no experience with a gpm system. And like I said, Im building one of these ships regardless, so I'll play however the majority of captains want to.
