T-Pain Is On A Boat: Re: [Electric Boats] 48V to 12V

Friday, February 18, 2011

Re: [Electric Boats] 48V to 12V

If you overload a DC to DC converter it will overheat and the voltage will start dropping.

We usually pair two DC to DC converters together and run them in parallel. Additionally, we mount both the converters on a large heat sink.

It is a good idea to have a 12 volt battery as an option for supplying 12 volts in the event that the converters fail. Its no fun being in the dark with all your sophisticated electronics when you are crossing a shipping lane. Also, if a DC to DC converter fails, it does so immediately, whereas if there is a battery in the circuit you have advance warning and can turn off non-essential items and go into a reserve power mode.

I am in the process of developing a charger that will accept 48 volts in and output a 3 stage charge algorithm at 12 volts, with complete control over the charging algorithm. It should be able to provide 50 amps or more of power at 12 volts - enough to run a windlass if you wanted to. We may be testing as soon as next week.

You will be interested in knowing how we have accomplished this and I will keep you informed.

If you are using DC to DC converters they will not properly charge a battery and may not like a battery in the circuit at all. One company does provide a battery charger option - but it doesn't do a charge algorithm or any more than 13.5 volts at any time, so it doesn't do a bulk charge properly and the battery will fail over time. It will keep the battery on a float and in reserve, but I would charge it from another source. Also, like most components I find that DC to DC converters are almost always over rated, so de-rate them if you plan to use them continuously.

James

Propulsion Marine

On Feb 18, 2011, at 6:39 PM, Byron Evetts wrote:

The 48v to 12v thing is about beaten to death.

Consider a GEM car, maybe the most popular electric car on the market. It takes a 72v pack and converts it down to 12v for accessory use. Do the same on the 48v boat. 48v converter to 12v for fun stuff.

But my GEM car will not sink if my main switch is off (and kills the bilge switch). So have a dedicated battery or tap a single bank battery to run your single bilge pump. In line with a fuse and float switch. Period.

All this" 4 pumps in series stuff" means ..when you need it most none of your 4 pumps will run. And then you have 4 switches in parallel for each of your bilge areas so it only gets more complicated and complicated is bad on a boat. And you're running 48v thru a 12v float switch so by now your boat sank or burned up..etc.

Run 48v to your drive train and 12v via converter to your accessories. Have fun.

Byron

From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of luv2bsailin
Sent: Friday, February 18, 2011 8:03 PM
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] 48V to 12V

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!
> >
>