Saving $ on electric filler pump (ideas?)

uhmgawa · Jun 22, 2004

( I found a rotary timer 0-30mins on Ebay for $2, so it should be here soon. Once I get it, I'll see what circuit and components will work best.)

Verify the contact rating on the timer switch is sufficient for the
amperage draw of the pump motor.

( Dumb question, though. If the trickle charger is left attached to the battery, as is the line to the rotary switch, then to the motor, will the high current draw harm the trickle charger? Is there some component I have to add to protect the trickle charger during the usage of the pump?)

Most likely not an issue for a mass-market trickle charger which
is designed to be placed across a battery of arbitrary charge state.
The trickle charger will be internally current limited. Then again
you won't be placing as large a load on the battery compared to
cranking an engine starter.

Soundguy · Jun 22, 2004

( If the charger has a full wave bridge rectifier neither the pump motor nor
you will notice the difference between using it vs. a 12 battery.
)

Keep in mind that a full wave bridge still puts out 'unfiltered' dc, as it is chopping and flopping. Makes a decent positive waveform on a scope.. takes a hit on average power a bit when under load.

( One point of caution is the running amperage draw of pumps in this class
is around 20A. So you may want to verify the charger/transformer can supply
this for at least the intermittent basis the pump will be running. It would
also be a good idea to size for current draw on both motor startup and
when dead-headed with the relief valve bypassing. )

That's why I sugested a charger across a battery... Even an atv battery.. The battery will more than adequate to source the needed current.

( You may find it simpler to use an inexpensive
30A 12V automotive relay )

I agree.. a sealed relay is the way to go...

Soundguy

uhmgawa · Jun 23, 2004

( Keep in mind that a full wave bridge still puts out 'unfiltered' dc, as it is chopping and flopping. Makes a decent positive waveform on a scope.. takes a hit on average power a bit when under load.)

The motor speed is proportional to the average voltage seen by the motor.
The voltage output of common battery chargers will peak in excess of
12V being 12V RMS. If full wave rectified this will still have a 120Hz
component, however this is will not impact motor speed/torque.

Soundguy · Jun 23, 2004

( If full wave rectified this will still have a 120Hz
component, however this is will not impact motor speed/torque.
)

Current will still be an issue. Even on a hih output charger.. or one with a 'starter setting'.. I've noticed that the high current setting on many of them are at quite a bit under 12v.. more like 8-10v to provide the 'stated' current under load on the label. For instance.. the 50 amp start setting on my charger, with volt meter across the battery will drop to 10v under light load ( lawnmower ).. and 8v on my antique tractor.. The battery sources more of the current, and faster providing it is good and charged.. lot easier than generating it ( just use the stored energy instead.. )

Soundguy

kensfarm · Jun 23, 2004

I use a 12v deep-cycle marine battery.. they have the regular battery terminals.. plus the bolt-on connections as well. The pump uses the bolt-on connectors.. and when the battery runs down.. I just hook up the battery charger on the terminals.

uhmgawa · Jun 23, 2004

( Current will still be an issue. Even on a hih output charger.. or one with a 'starter setting'.. I've noticed that the high current setting on many of them are at quite a bit under 12v.. more like 8-10v to provide the 'stated' current under load on the label.)

Quite possibly for an inexpensive charger. Voltage drop
under increased current draw is primarily an issue of internal
resistance in both cases of transformer and battery, with
the battery having additional limitations as seen by Peukerts
Effect, etc.. However on any 'charge' setting the voltage
output must be greater than the series cell voltage or the
battery will not charge.

Subject to available ampacity, discharge cycle depth/draw/duration
a battery makes for a fine solution to power the pump under
discussion. My first choice would be the one in the tractor as
it is already there complete with it's own charging system as
well as showing up when the tractor needs to be fueled. It also
has the poetic property where if it can't power the transfer pump
you really don't need more fuel in the tank.

Soundguy · Jun 24, 2004

( However on any 'charge' setting the voltage
output must be greater than the series cell voltage or the
battery will not charge.
)

That's a real non-issue here, since the original idea was to run the pump just off the battery charger.. with NO battery in parallel. In that case there is -NO- charging occouring.. the charger is simply an unfiltered dc power supply that may or may not offere sufficient voltage/current to power the pump acceptably when under heavy load. That's why I suggested a battery in parallel in the first place. Undoubtedly with the battery in parallel footing the bulk of the load, charging and voltage drop will not be an issue.. unless the pumps current consumption exceeds that of the battery and charger's combined output.

I also like the idea of powering the rig from the tractor system.. say like from a cig-lighter plug. I mounted one under my tractors hood, directly across the battery.. for tire pumps and inverters and such.

I think the original poster didn't want the electrical connection outside though...

In any case.. he has tons of options now.

Soundguy

uhmgawa · Jun 24, 2004

( However on any 'charge' setting the voltage
output must be greater than the series cell voltage or the
battery will not charge.

That's a real non-issue here, since the original idea was to run the pump just off the battery charger.. with NO battery in parallel.)

The point was not to charge a non-existent battery but to
illustrate the charger in 'charge' mode would need to be
capable of delivering greater than battery voltage at its
rated charge current. Otherwise it would be unable to charge
'a battery'. Thus this equivalent charger-supplied voltage and
current would be available to power the pump with no battery
present.

Soundguy · Jun 24, 2004

( The point was not to charge a non-existent battery but to
illustrate the charger in 'charge' mode would need to be
capable of delivering greater than battery voltage at its
rated charge current. Otherwise it would be unable to charge
'a battery'. Thus this equivalent charger-supplied voltage and
current would be available to power the pump with no battery
present.
)

Yes.. and I was pointing out that a charger capable of handling a high enough continous charge current to run a decent pump is going to be a lot more expensive than a cheapo battery and float charger...

Looking at the small fuel transfer pump at work on the back of the mechanics truck.. it needs 7-8 amps... the larger pump on our 500 gallon tank wants 10-12 amps

While my cheapo 1.5 amp battery charger was 10 bucks.. my 2/10/50 was 69 bucks.... ( decent brand.. not a chineese special... has a meter, safety features, and float position /auto shutoff when in 2 amp mode)

A 29.99 battery from wally-mart and a 10 buck charger will run a decent pump way better than a charger you could get for 39.99... That's the point I'm trying to make... Not that it isn't feasable.. just that it isn't cheaper to do it that way..

Soundguy

uhmgawa · Jun 25, 2004

( .. just that it isn't cheaper to do it that way.. )

If cost is a primary concern another possibility is a cast-off
AT/ATX PC power supply -- many of which can provide
in excess of 20A at 12V. Some experimentation may be needed
as a few designs behave poorly if the 5V output is unloaded.