12v step down module?

[Raskal311]

I’m looking to install two 12v batteries in a battery box to run my FF and bait tank. To run the bait tank I’d like to install a 12v Step down module to run the bait tank at 7.5v/3a. My question is would running a step down draw less juice giving me longer battery life similar to running a 6v battery direct?
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http://www.amazon.com/Converter-Step-Power-Supply-Module/dp/B00CXKCOPY/ref=sr_1_7?ie=UTF8&qid=1376406444&sr=8-7&keywords=12v+step+down


BTW I have a hobie live well which is 12v 3amp.

[Baja_Traveler]

No.

Unless you go very high dollar, step down transformers use resistors to drop the voltage, wasting the excess energy as heat.

[alanw]

Be careful with these. If it is an electronic circuit then even if it is waterproof it may have condensation issues like my oex bait timer did, which caused it to fail after only a few outtings.

Personally I avoid adding anything extra between my batteries and electronics because it's just adding another potential failure point.

To answer your question, on the item you linked I would expect it to draw 3A constantly from your battery. But, if I were to buy one of these I'd surely check it's actual current draw during use, and be prepared to return it.

[Raskal311]

Wow I'm glad I asked. Thanks fellas

[alanw]

Originally Posted by Baja_Traveler

No.

Unless you go very high dollar, step down transformers use resistors to drop the voltage, wasting the excess energy as heat.

Actually step-up/down transformers don't generally use resistors, they just use coils and an iron core. Using resistors to achieve a voltage drop is a simple circuit that does indeed burn off excess energy as heat.

[bus kid]

http://www.mofoco.com/item/Empi_9384...Bug_/513/p2c62

[danjor]

If it was me I would use a PWM controller that way you can adjust the duty cycle to whatever water flow you like. I am currently using the on off timer style controller from OEX but when I get some time I'm planning on setting up a PWM controller to control my bait tank pump since the on off sounds good on paper but it turned out to be annoying to me.

[makobob]

Why not do what most of us do. 12v for FF and 6v for bait tank? I got 14 hours on a lifepo4 and it still will run the pump maybe another 6 hours. And it only weighs less than 2 lbs.

[iethinker]

Raskal,

The type of device you have suggested will work fine allowing your main dual battery system all to be at 12-volts. This is very convenient for recharging the parallel battery system. Just be sure that the amperage your bilge-pump / bait-pump draws at 7-volts does not exceed the 3A limit of the DC/DC converter. The converter itself will not consume unacceptable excess power and is totally sealed. All of this is of course assuming you wire things correctly. Go for it!

BTW...the resistor suggested by bus_kid will only work if the resistance load of your bait pump is the same as the resistance of the wiper motors of an air-cooled Volkswagen of some vintage.

iethinker

[Raskal311]

My second option is to go Lifepo4.

[alanw]

It's only 8 bucks, it won't hurt too bad to try it. Just check the current draw while using it.

[Raskal311]

That's true

[PescadorPete]

Here is the answer to your question, based on some science and some assumptions, with the Hobie bait tank pump.

12V battery directly connected uses 16.5 watts of power (and way too much water flow).
12V battery and the resistor uses 6.3 watts of power.
12V battery and the step down module uses 5.6 watts of power.
12V battery and the PWM uses 4.3 watts of power.
6V battery directly connected uses 3.2 watts of power.

Watts is what gets the work done and what the battery needs to supply, so in simple terms, ignoring a few messy details, the 6V battery is the most efficient and will last the longest. That's what I use on my Hobie.

Here is a photo of the elusive PWM. I put it together many years ago for my 12V (non-Hobie) kayak and its still works well.

Enough science for now, my head hurts, lets go

[Raskal311]

Originally Posted by PescadorPete

Here is the answer to your question, based on some science and some assumptions, with the Hobie bait tank pump.

12V battery directly connected uses 16.5 watts of power (and way too much water flow).
12V battery and the resistor uses 6.3 watts of power.
12V battery and the step down module uses 5.6 watts of power.
12V battery and the PWM uses 4.3 watts of power.
6V battery directly connected uses 3.2 watts of power.

Watts is what gets the work done and what the battery needs to supply, so in simple terms, ignoring a few messy details, the 6V battery is the most efficient and will last the longest. That's what I use on my Hobie.

Here is a photo of the elusive PWM. I put it together many years ago for my 12V (non-Hobie) kayak and its still works well.

Enough science for now, my head hurts, lets go

Holly cow... you are the MAN!. So a 6v 9amps direct the battery should last 18hrs give or take? Good enough for me, time to grab a new 6v.

[StinkyMatt]

Basic fishing rules:

Everything you were promised .....subtract 25%

18 hours I duuno. Maybe when its perfect new condition.

[PescadorPete]

My new 6V 10AH lasts 10-12 hours (one of those messy details I spoke about).