DC/DC Converter vs Second Battery - Page 2 - Fuel Economy, Hypermiling, EcoModding News and Forum

puddleglum · 01-08-2018, 10:45 PM

Update, I tried the dc/dc from the forklift through a diode to prevent any reverse current from the alternator. That was a fail. There was a voltage drop through the diode and output voltage was too low to do any good. At least I know now.

Round two. I mounted the two small dc/dc converters I have in parallel, set the voltage to 14 volts and didn't bother with the diode. They aren't reverse polarity protected but I figured it won't matter as long as output is close to Alt. voltage. Time will tell if they last. Today was the first test and it seemed to work okay. They don't have enough output to keep up with head lights, but battery doesn't pull down as far or as fast. With just clearance lights and DRL's it's fine. I may still try it with the diode and see if it works. I notice the dc/dc's stay on all the time when connected to the 12 volt battery. I don't think they will draw much to keep the caps charged but it's not ideal.

puddleglum · 01-16-2018, 01:03 AM

Here's my DC/DC converter installed. It seems to be working so far. I haven't decided yet if I will use it once biking season returns. I may revise it again.

teoman · 01-29-2018, 05:29 AM

This looks like a good solution.

If you can find junk batteries, one could use those to boost the range of your battery.

Stubby79 · 01-29-2018, 10:21 AM

Looks good. Nice work.

Looks familiar too. I have one of those same converters!

teoman · 01-29-2018, 02:27 PM

I have ones that are good for a coupe of amps. They also work as boost converters that can display the volts amps etc...

I am thinking of making lots of small packs of different chemistries that are easier to manage (for me)

puddleglum · 01-29-2018, 10:56 PM

I tried it like this without the diode for a week or so and it worked great, but I found my charge light on the dash would flash on and off during EOC. I presume the voltage regulator in the alternator was cycling on and off but not sure. Anyway, I was concerned that I may damage something long term so I put the diode back in. Seems to be working well now.

Quote:

Originally Posted by teoman

This looks like a good solution.
If you can find junk batteries, one could use those to boost the range of your battery.

I have a bunch of old laptop cells that I was going to use for a spare e-bike pack. I'm thinking I may cobble them together for the car instead when I need to pull this pack out to put back on the bike in the spring.

teoman · 02-03-2018, 06:12 PM

What voltage are you charging your car battery at?

puddleglum · 02-04-2018, 03:09 AM

The DC/DC's are set to 14.1 volts, same as the alternator. They have no reverse polarity protection of there own so I didn't want the alt. to blow them out. Through the diode, they charge at 13.3 volts. This seems to be working for now.

teoman · 02-04-2018, 03:28 AM

On my car and motorbike, at 14.1 V it always draws some amps. (From adjustable power supply with amp meter to battery).

Not much, but you are constantly wasting a bit of energy.

Then again the car may not be happy if voltage drops further.

puddleglum · 02-04-2018, 04:36 PM

I agree, that was another reason I thought the diode would be a good idea. The battery is now only seeing 13.3 volts. I haven't put an ammeter on it, but I think the draw to hold it at that voltage should be very little and 12v battery is no longer trying to keep the dc/dc's charged when the supply battery is turned off. I have a switch on the 24v pack to turn it off when I'm not driving the car so the only time it is trying to charge the 12v battery is when I'm driving, or when I forget to turn it off