There's one other down-side to the series-pump approach, you're increasing the statistical chance of pump failure by a factor of 4. If one fails open they're all out of commission.
Jim
--- In electricboats@yahoogroups.com, "Myles Twete" <matwete@...> wrote:
>
> This is a good point.
>
> And while you are right that the voltage difference between any two such
> pumps in series may be different, the current in each motor would be
> identical. Which is more important in this case, current or voltage? If
> torque is important, and indeed the ability to lift or pump is more
> concerned about torque than speed, then this series arrangement is not in
> itself a showstopper or unworkable. The question seems to be really what
> happens under the range of loads:
>
>
>
> Case 1: TEST (no pumps immersed in water)---the pumps will each attempt to
> reach the no-load speed of 12v/Kb. Sure, there'll be differences, but not
> much.
>
>
>
> Case 2: One pump immersed --- That pump requires more torque, it's speed
> drops, current goes up and the drop in voltage ends up going to the other 3
> pumps, speeding them up. That's not much of a concern. But what may be of
> concern is the fact that the loaded motor might not be able to draw the
> current it needs as the other unloaded motors can't accept much more current
> without being loaded or allowed to speed up substantially. This case is a
> problem.
>
>
>
> Case 3: Two to 3 pumps immersed --- This is likely less of a problem, but
> similar effect as the above.
>
>
>
> Case 4: All 4 pumps immersed --- No problem---each pump is working hard, its
> speed and voltage dropping somewhat and allowing higher current (and torque)
> to flow.
>
>
>
> So to pursue this solution right, one would probably want to provide a means
> to bypass current around motors that have reached their rated voltage and
> aren't loaded. As this may complicate things more than other solutions,
> this approach is problematic.
>
>
>
> In case this helps-
>
>
>
> -MT
>
>
>
> From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
> On Behalf Of greenpjs04
> Sent: Friday, February 18, 2011 2:08 PM
> To: electricboats@yahoogroups.com
> Subject: Re: [Electric Boats] 48V to 12V
>
>
>
>
>
> Kevin,
> If you have 4 pumps in series connected to 48 volts, you are only guaranteed
> that the total voltage is 48 - not that each pump sees 12 volts. If some are
> dry, some are wet, and some are clogged, etc, you might have 6 volts on one
> pump, 8 on another, 20 on the third, and 14 on the last one. That adds up to
> 48 volts, but pump one will bog down and stop while pump 3 will spin way too
> fast. That is not a workable situation. Only if all 4 are identical (both
> manaufacturing specs and the load) will they see 12 volts each.
>
> Pat
>
> --- In electricboats@yahoogroups.com
> <mailto:electricboats%40yahoogroups.com> , Kevin Pemberton
> <pembertonkevin@> wrote:
> >
> > Pat,
> >
> > I think so. the idea is 4 pumps in series activated by one switch. This
> > is not 4 switches activating each pump that is tied in parallel per
> > battery. Should work and sounds like quite an Idea. Think about it, the
> > bilge gets pumped even if one or two pumps become clogged.
> >
> > Kevin Pemberton
> >
> > On 02/14/2011 04:53 AM, greenpjs04 wrote:
> > >
> > > Perhaps I have misunderstood Myles' suggestion, but when putting
> > > anything in series, balance becomes important. If the four twelve volt
> > > pumps are identical and loaded identically, then each will see 12
> > > volts. However, if 3 are dry and one is wet, the wet one will have a
> > > higher load and its voltage will drop causing problems. If the pumps
> > > are tied to each individual battery, then some of the problem goes
> > > away, but the original objective of keeping all four batteries
> > > balanced still hasn't been achieved since the four loads can vary by
> > > quite a bit unless all four pumps are loaded equally (all pumping
> > > water of equal depth to outlets at the same height).
> > >
> > > Pat
> > >
> >
> > --
> > Ubuntu10.04, Acer AspireOne, Virgin Mobile 3G Broadband2go.
> > Doesn't get any better than this!
> >
>
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