[John Walker]

This is mainly for the Techies and Leckies...

I have never used my 100psi pump at full speed or even needed to.

I have checked the voltage going to the pump via my Variflo.  It reads 6v at the setting I have been using for many months.  Unfortunately the Variflo occasionally has a mind of it's own which is a pain.  It always seems to happen when I'm away from the unit and i have to walk back to turn the flow control slightly.  Sometimes it restarts while i'm walking away which is even more of a pain.  I've tried various internal settings which have helped but it's not perfect.

My thoughts were then to see if I could go back to a basic hard wired non-electronics set up.

So....  I've tried a 2 ohm dropper resistor in place of the Variflo and this gives me a constant 6v at the pump - giving between 1.5 and 2 litres per minute flow from the brush - perfect!!   However - I can't source a high enough wattage resistor that's man enough for continuous running without getting seriously hot. 

I then thought - why use a 12v battery when I only use 6v - what about a 6v battery.  If it will work - it does away with all the electronics and makes for a very simple and robust system.

I don't want to run the pump at full speed with a by-pass to control the flow.  If I can get this to work, it will be less wear on the pump etc than using a by-pass.

Not sure if it's possible to get the right sort of 6v battery though.

Any thoughts gents.....

[jeff1]

I used these resistors when installing CCTV and I utilised the heat to keep the glass demisted http://www.arcol.co.uk/product-range/product-series.php?cid=3&pid=62 

they have there own heatsink to dissipate the heat.
Without sitting down doing all the calculations I'm unsure it will work in the long term with a 6v battery because of the current drawn from the pump.

Probably the cheapest way would be to use a 7806 voltage reg with external current boosting transistors mounted on a heatsink...

The most appropriate way would be to use a switched mode regulator..

[John Walker]

I used these resistors when installing CCTV and I utilised the heat to keep the glass demisted http://www.arcol.co.uk/product-range/product-series.php?cid=3&pid=62 

they have there own heatsink to dissipate the heat.
Without sitting down doing all the calculations I'm unsure it will work in the long term with a 6v battery because of the current drawn from the pump.

Probably the cheapest way would be to use a 7806 voltage reg with external current boosting transistors mounted on a heatsink...

The most appropriate way would be to use a switched mode regulator..

Hi Jeff

Thanks for all the info.  I managed to find one of those resistors on Ebay at a good price so have ordered and will give it a try.  Using a lower wattage resistor worked perfectly and I left it on soak test for 30 mins.  The water flow was perfect and such a simple system - far less to go wrong.  The only problem I had was the resistor I used was getting hotter than I was comfortable with. - Perhaps I should have had it in the water tank as a heater!!

I'm sure that mounted on a heat sink, the resistor you have suggested will do the trick.  If in practice it doesn't work - no problem.  I will leave the Variflo in place and it's a 2 minute job to connect it back in.

[jeff1]

Why not use your head on this one lol

Stick a 55w bulb in series with your pump and you'll have light at the same time.

What ever method you use it will still be drawing plenty of current from your battery.

If you screw the wirewound resistor heatsink case to the van floor the van floor will become a much bigger heatsink so the resistor will run much cooler, mind you I think it would take a few weeks to take the chill off the water by sticking into your tank lol

[John Walker]

Why not use your head on this one lol

Stick a 55w bulb in series with your pump and you'll have light at the same time.

What ever method you use it will still be drawing plenty of current from your battery.

If you screw the wirewound resistor heatsink case to the van floor the van floor will become a much bigger heatsink so the resistor will run much cooler, mind you I think it would take a few weeks to take the chill off the water by sticking into your tank lol

Hi Jeff

I did wonder about using a bulb but wasn't sure about the resistance characteristics between a cold filament and a hot one - still it would be cheap to try it.  I have a bit of electrical knowledge - but I often fall at the last hurdle.

Thanks again
John

ps. It's pretty quiet from other posters - they're probably thinking - what the fffff is that John Walker on about now !!   

[jeff1]

rofl They may be thinking is that his name Johnny Walker or what he's drinking 

Let us know how you get on.

[Ian Lancaster]

Hi John,

Is it just that you don't want to run your pump flat out?  What's wrong with just adjusting the pump setting?

I've just had to change my 60psi Flojet (it froze in the last cold snap and now it makes horrible noises so I'm going to open it up and see if I can renovate it) I've put in my spare 100psi Shurflo but turned the pressure down so I get a reasonable flow without overdoing it.

I just have a simple toggle switch between the battery and the pump, with a 15amp fuse in the line.

The pump works fine, gives a nice gentle flow and cuts off within a few seconds when I disconnect the pole.

I'm probably telling Granny how to suck eggs, but there's a tiny Allen screw in the pressure switch cover.  Turn this one way to increase pressure/flow and the other to reduce it.

No need for bypass