Redbelly wrote:
eb145 wrote:
This device definitely increases the amps going into the battery. something like 2 Amps without it, and up to 20 Amps with it (till truck fuse blows). It does this by raising the voltage closer to the battery terminal. Your idea of boosting to 72 volts for the long distance run on the existing truck wire and then dropping to 14+ volts is very interesting. Increasing the voltage by a factor of 5 or 6 will reduce the current by a factor of 5 or 6.
300W/72V = 4.2 Amps on the truck wire which is way under the 15 Amp limit for 14 gauge wire.
Ed
Ed, I'm impressed with what you've done as I've been messing around with a similar concept, mounted as close to the trailer battery as possible.
A couple of what-if questions.
Ebay sells a $25 version of that DC-DC booster that is rated at 400 watts and has potentiometers that allow you to adjust both maximum voltage and current. What if you used one of these instead?
http://www.ebay.com/itm/111177068259
Second, why couldn't one use a solar panel controller in series with the battery to regulate the battery charge rate? You can pick up a charge controller for $15 that will measure the battery state of charge and regulate the input voltage to keep from overcharging it.
http://www.ebay.com/itm/12V-24V-5-10-15-20-30A-PWM-Solar-Panel-Battery-Regulator-Charge-Controller-/351004581852?pt=LH_DefaultDomain_0&var=&hash=item51b980dfdc
The DC-DC booster you link to above is still a max of 10Amps output, but it can be set to limit current which is better than what I put together. It looks like it has a microprocessor that lets you set the voltage and current. Pretty cool.
Putting a $15 PWM solar controller would work but it is not necessary for the specific use case I have in mind for it.
If I was going to wire this in to be a permanent part of the trailer charging circuit I would buy one of the commercial products where they (hopefully) have built them with safety in mind. Ctek builds one that is interesting: CTEK D250S for $180 on Amazon that includes a MPPT solar charge controller feature.
CTEK D250SAs far as my special use case, I intend to use this 2 or 3 times a year while camping and my solar can't keep up (due to deep shade). It works better than my cheap jumper cables alone. And I don't want to get a generator. And I'm really enjoying this whole battery charging game.
I actually intend to let the trailer batteries charge off the truck battery (with the truck turned off for the first hour or two). My gizmo can transfer 10 or 20 Amps from the truck battery whether the truck is running or not. I'll only let maybe 10 or 20 Amp Hours move from the truck battery, then start the truck and let it run for another hour. My 180 Amp truck alternator can easily charge the trailer batteries and the truck battery simultaneously.
Or I might transfer 20 or 30 Amp hours *silently* from truck battery to trailer batteries right before I plan on going for a one or 2 hour drive in the truck. That will let the truck batteries recharge from the alternator without having the truck running at the campsite for an hour or two.
If I screw up and drain the truck battery too much to start it, then I'll get a jump from a friend and accept a lecture from my DW.
I don't plan on leaving this gizmo operating when I am not around to closely monitor it. Westend is right to point out safety issues using wood and cheap plastic for this type of thing. Obviously I have no metal working experience - my father is a carpenter so I know how to do basic wood stuff.
And mex points out the lack of heatsinks. The dc-dc converters I bought specify to do something about additional cooling if you want to operate at the max rated 10 Amps. That is why I added the muffin fan.
Now I'm thinking of some changes in construction... using metal to provide heatsink capability and fire resistance.
Ed
