New Battery + Solar Charger

[Loren]

Been thinking about this for a while. Had to use my jump-pack to start the Mirage when I was out shopping today, so it's time to take action! I pulled the trigger on a few parts tonight.

The problem is this: I've installed a kill-switch, and I use it a lot. Most of my trips in the Mirage are fairly short, usually less than 20 minutes. With half that time in an engine-off coasting state, the battery isn't getting charged as it should. Couple that with the fact that I'm using an 8.6AH battery... well, it's no wonder I ran out of juice! (on the plus side, I usually see between 50 and 60 indicated trip MPG, which is cool)

So, I'm going at this problem from two directions.

First, I'm going to give myself nearly 4x the battery capacity (while only increasing the weight from 11 pounds to 17 pounds, or something like that) The new battery is just a larger Motorcycle battery with 30AH capacity, and over 300 CCA. Compared to my 8.6AH battery with 170 CCA, it's a monster!

That will give me more battery capacity so that I can drive with some accessories on without killing the battery so much. And it is an AGM battery, so it should be fairly tolerant of more discharge than a standard car battery. ($65)

Second, I've sourced a 20W solar charger. On a nice, sunny day, it should produce about 20W at 14.5 volts. (and I do live in FL, so we get some sunny days) That's about 1.4 Amps, which should be a good safe trickle charge. ($48)

I did some research on this a few weeks ago, but I forgot most of what I learned. The conclusion that I came to was that with a 20W charger, I should use a charge controller. So, I'm including a Battery Tender 5-45W Solar controller in the mix. That will keep the battery from overcharging, and also keep the solar panel from draining the battery at night. ($24)

With all of this, I won't have to haul out the AC charger and actively charge the battery, but most of my drives should start with a freshly charged battery. And I'll have enough capacity to start the car repeatedly and make my short trips using as much EOC as I care to.

If my goal was LONGER drives, then I'd probably need to fit a much larger capacity deep cycle battery. Thankfully, I don't need to accommodate that, which means I don't need a more expensive and heavier battery!

[Loren]

So, for those who have done silly things like this before (looking at you Daox), I have but one question.

I may mount the solar panel on the dashboard (I have tinted windows, only the windshield is clear), and I'd like to wire this thing without punching extra wires through the firewall.

So... I know there are some circuits on the fuse panel under the dash that supply 5 amps of unswitched power. Being unswitched... they should be a direct connection to the battery, right? Any reason I couldn't just tap into one of those to feed a sub-2 Amp charge to the battery?

It would sort of be like using an always-on cigarette lighter socket. But, the lighter socket on the Mirage is switched, and I also have my phone charger plugged into it.

[foama]

Whatever you do, make sure you have a fuse of the correct size (max 5A) and in the right place. It should be installed in such a manner, that if any of your additional wiring shorted to ground, the fuse would prevent a fire.

The regulator should provide a max output of no more than around 15V in the cold season, and no more than 13.8 to 14.0 Volt in the warm season. The reason being lead-acid batteries produce gas and lose water dependant on both voltage and temperature.
For example, a 12V battery begins gassing at 14.4V and +20°C, 13.8V at 30°C, and at over 15V at 0°C.
An addition to that, a sealed (gel) AGM battery has its own special properties, in particular the charging current has lower limits.

[Eggman]

Better to wire direct to the battery rather than put an external source of energy on a circuit not designed for it, especially if this new source can affect other circuits and functions. Just my 2₵. The solar panel on the dashboard idea should work great.

Before long you’ll be doing Mirage hybrid drivetrain research.

Have you seen the Mirage AS&G setup? They get a larger battery and alternator. Change the alternator to a generator and...

[Loren]

Given the typically "frail" wiring of the Mirage, I totally get what you're saying. But, if a circuit is designed to carry 5 amps in one direction, then it should be able to carry 5 amps in the other direction. And I'm only charging at about 1.5 amps.

Proper fusing is a given.

Kinda looking forward to playing with this, but I've got to finish my garage cabinet project before I do it. I've been putting that project off for 9+ months, and I'm about 3/4 done with it now. Then I'll have a nice workbench to do stuff like this on!

[Daox]

Yeah, using existing wiring is fine. Foama is right about the charging though. You have a couple options. At minimum you need a diode. A solar panel wired directly to a battery will slowly drain it if it isn't in the sun. This diode will have to be rated for the full current your panel can put out. Number two is a proper charge controller which will charge your battery at max amperage until the correct voltage. These can be had fairly cheaply on Amazon or eBay. Its nice if you can find one with a overcharge or shunt feature. I forget what they call it, but basically once the battery is topped off, it'll divert what extra power it has to another load. This is handy if you want to use your excess power for something like... running your cabin fan in summer to automatically keep your car cooler.

As a side note I noticed just the other day that my alternator delete (charging at 15V when on) did make my battery loose a fair amount of water over summer. I'll be updating that thread shortly. I had to add water to it and it wasn't an insignificant amount either. Granted, it was charging at 50-80 amps when it was on, not 1.5.

[Loren]

Y'all missed the part where I'm putting a Battery Tender solar charge controller in the circuit to keep the battery from overcharging AND discharging.

So, last night and today some of my stuff showed up. I don't have time to be messing with it right now, but I couldn't resist a little casual testing.

The panel itself has some kind of control circuit on it. (it claims to do the same thing that the Battery Tender does, but I trust the Battery Tender a lot more than some random bit of Chinese circuitry) It seems to limit output to 14.3 volts.

On my bench in the garage with ambient light, it put out about 4.5 volts. In the sun, or partial shade... pretty much anywhere outside... it was a constant 14.3V.

Current varies, of course. I tried to measure it, but wasn't getting anything on my meter. Could be operator error. Could be a blown current limiting fuse (it seems to always be blown when I want to measure something, why is that?), didn't bother taking time to figure it out, or to grab the other meter.

I did have a standard 1157 tail light bulb handy, so I hooked that up and monitored. Voltage drop measured across it was much less than 14V, more like 9-11. It increased in bright sun, and decreased in shade. And the brightness of the bulb varied with it.

I was on the smaller tail light filament which is normally rated at about 8W at 14V. So, if I was getting full output from the bulb, it would be around 1.75A. I wasn't getting full brightness, but it did get pretty bright in full sun. 8W at 10V would be 1.25A. That's probably about what I was seeing. That all passes the basic BS test. Seems to be outputting what it should.

I hooked up the Battery Tender. Its yellow status light blinks when there is sufficient power for it to work. And it did just that. Measuring input voltage on the Tender, it was fluctuating between about 13.3 and 13.7V, and would vary depending on amount of direct sunlight. Couldn't measure the output of the Tender without connecting it to a battery. (it's designed to not output anything if the battery it's connected to is below a certain threshold of voltage)

So, initial tests of the equipment are as expected. Still waiting on the new battery. It's slightly larger than the old one, so I'll have to do some fabrication on my battery mount bracket to fit it. Then I can get into wiring.

Thinking about putting a voltmeter on the dash somewhere with some switching so that I can monitor either the solar supply voltage, or the battery voltage. Driving, I want to monitor the battery. Solar voltage is just "gee-whiz, that's cool" stuff. But, I can put it on a switch and have that info at my fingertips!

[Loren]

Laziness won on the voltmeter. I opted to order a lighter socket voltmeter with a built-in USB charger to plug my phone into. It's got a green light ring around it that turns red and blinks when voltage gets down to 11.5V. Perfect!

[Loren]

Finally got back to this today.

Was out doing some other stuff to the car yesterday and noted that the battery (the old 8.6 Ah battery) didn't have enough juice to start the car. It had been resting for a couple weeks, and that battery is getting pretty weak, anyway.

I've got the new slightly larger battery waiting to go in (I'll probably have to do some fab work on the brackets to fit it).

But, I decided to just wire in the solar charger first and see if it could revive this battery. Should be a good experiment, assuming the old battery isn't just toast.

So, I got another of my micro fuse taps. Found an unused "hot" accessory slot, got that all set up and verified that it was indeed providing 12V with the ignition off. That means it's a direct connection to the battery. And I put a 5A fuse on it, so nothing bad can happen.

I tapped another ground wire onto a convenient bolt under the dashboard right next to the fuse block. So, that gets me + and - to the battery.

From there, it was a simple matter of wiring the output from the solar panel to the input of the Solar Battery Tender widget, and the output of that to my new-found battery connection. Very simple and tidy.

With the solar panel on the dash, and the top of it suction cupped to the windshield, it's charging. The light on the panel controller lights up (and I'm pretty sure it does the same job as the Battery Tender... but, I wanted to be sure, so I have both). The Battery Tender light blinks when the input is connected to let you know that it has DC input.

Then when connected to the car battery, the Battery Tender light goes solid to let you know that it's charging. So far, so good!

When I first went out to the car, the battery was at like 11.5V. I was careful to not leave the dome light on while I was working with the door open, but fidgeting around turning the power on and off throughout the process bled it down to 9.3. (no wonder it wouldn't start the car yesterday!)

When I first plugged in the charger, the battery voltage (at the lighter socket, which requires the ignition to be on) read 9.5V. So, right away, I knew it had to be charging. Over the course of a half hour while I was cleaning up, I saw it go up to 9.7V, so I know it's charging. Max 1.3A, though... so, it's not going to be fast.

After about 90 minutes, I went out and saw 10.3V on the meter, but it quickly dropped to 9.7. It'll get there.

I'm going to leave it alone until tomorrow afternoon. That should give it at least 6 hours of morning sun, we'll see where it's at then.

If I can get enough juice into this dead-ass battery to start the car using nothing but the power of the sun... I'm going to call this a great success! Then I'll move on to fitting the new battery and properly mounting my wiring and stuff.

Photos to come.

[Loren]

Here's what the panel itself looks like. I could maybe move it further to the right and leave it there. But, it's probably going to be intrusive while driving, so I can just pull the suction cups and lay it on the dash... or I could unplug it and put it behind the seat.


This is the controller on the back of the panel. It seems to limit the output current, and it's supposed to prevent overcharging and also prevent reverse current. (but, I don't trust it)


This is the Battery Tender. When I'm ready to final mount it, I'm going to tape over those connections and maybe velcro it in place under the dash somewhere.



And this is my cool little voltmeter.