Charging a starter battery via solar

[Blacktank]

so i run my starter dead flat,nothing there to activate the solenoid to use my house battery to start,no one around for a jump,to lazy to pull the house out and use it as the starter

a pigtail of two alligator clips going to a anderson power pole that i can hook my panel directly to the battery,in the sun this will be 20v+,would that voltage mess things up? would rather not fry my alternator,wires,fuses or whatnot , would just unlazy myself and switch batteries in that case


also any other way you can think of for me testing my house battery being able to start when starter is low besides just waiting around until my cheap truck battery gives up the ghost and using it as my dead starter in the van

[sternwake]

Hook both fat cables on solenoid to same terminal for self jumping.

Or.keep a fat jumper cable and extra nut to jump fat solenoid terminals. Give it a few minutes becofe cranking starter.

You can hook20v/12v nominal solar panel directly to battery termianls. Only danger occurs when battery gets above -85% and voltage could exceed 15v. Even then not all that dangerous.

[sternwake]

I was regularly hooking a 100 watt panel to my 12vdc system with no charge controller.  The only danger would be when the 100 watt panel by itself could overvolt the battery, as my regular charge controller will back off the output to 0 of my mounted panels in an attempt to keep voltage from exceeding 14.7v.

So 100 watts of solar panel is basically 5 amps in good strong sun.  There is no point in trying to recharge a dead starter battery to 100% before starting the engine so worrying about overvolting by direct connecting a solar panel to a dead starter battery, should be a non issue as once it is recharged to 50% it should easily be able to start the engine.

Some people will simply charge the chassis starter battery by running two wires to the engine battery, or gasp, the Ciggy plug mounted on dashboard from the solar recharged house bank.  Gary, Since you have anderson powerpoles and crimper, make a 10 AWG extension cord long enough to reach your engine battery.  Have a powerpole on the engine battery for a quick connect for mainteance charging of chassis battery when you have the solar feeding a full house battery.

 I now have two 8 awg  45 awg powerpoles right where an engine battery would be, if I had one.

This DC extension cord also comes in very handy.  I have something like 60 feet of 12v extension cords with anderson powerpoles on both ends, some are fused.  Some 'should' be but are not.  Some are 10AWG, some are 16awg 3 wire household extension cord with two wires on the negative side, one on the +.  I could in theory send some small  amount of current to a distant parked vehicle's battery, though voltage drop would be considerable depending on the length and gauge of the extension cables used.

One thing about hookng a panel directly to the battery.  i would recommend not having the panel in direct sunlight when hooking or unhooking the panel to the battery.  There will be a few milliseconds of 20V before the battery dampens it and these voltage spikes could conveiveably be cumulatively damaging to  things hooked to batttery.  Also the spark of current which jumps across the connector, will degrade the contacts faster.

Also some solar panels warn to not disconnect the panel from a load ( battery) while in full sun.  it could be cumulatively and perhaps possibly instantly damaging to the diodes in the solar panel.  So if direct connecting a panel to a battery or along the 12v system somewhere, Tilt the panel way from direct sunlight if portable, or cover the  mounted panel before connecting or disconnecting.

Whether the panel  or things attachd to battery will actually be damaged is of course unknown, and perhaps not an issue at all. but it could be cumulatively damaging and a risk, so i would recommend avoiding the risk, if possible or not too inconvenient to do so.

[tx2sturgis]

You can indeed hook up a solar panel directly to a discharged battery for charging, BUT...if the battery has failed OPEN...and it can happen...you may be applying about 21 volts to some sensitive vehicle electronics when you hook it up.

To be 100% safe, unhook one of the battery cables from the battery, usually the negative, then hook up the panel (observing proper polarity) to the battery, charge the battery, and check the voltage on it every 15 minutes or so. Also, its a good idea to remove the caps from a flooded starter battery and make sure the fluid levels are good, and you dont want to see active bubbling in some cells while none in other cells...a little bubbling in all the cells is normal.

Depending on the time of day, ambient temps, and how deeply discharged the battery is, it might take hours, or might not even charge it fully depending on the time of day and how soon the sun is going down. 

When it reaches 12.5v or more, unhook the panel and reconnect the battery to the vehicle.

If the battery is in reasonably good shape, it should have enough power to start the engine.

[Blacktank]

could just disconnect the starter battery before hooking a panel to it so you dont mess up any chassis electronics

maintenance charging,i like it,since i grounded my house battery to the frame the negative circuit is complete to the starter battery so a shunt on the positive just past the charge controller,quick connects and use the fuse as an on/off or should i use an actual switch?,positive wire going to my busbar,gm side screw battery not easy to add wires too,sound about right?

[tx2sturgis]

Using those 100 watt panels, maintenance charging is ok as long as the solar charge controller is involved.

Otherwise the battery will likely be overcharged and damaged.

BTW, in the past, actually since 1995, up to now, and currently, I use very small solar panels (different models and brands) connected directly to the starter battery for maintenance when my various vehicles have remained parked for days, or weeks.

It's especially effective in modern vehicles that have parasitic drain due to the security system and remote keyfob receiver, as well as door opening and closing which wakes up the ECM and turns on the dome lights, and operating the power door locks and windows.

This little Eco-Worthy 10 watt panel (more like 6 watts in actual use) is making just enough power to keep the starter battery topped-up on my pickup during extended time while not driven. It includes a blocking diode as part of the design.

       

https://www.ebay.com/itm/5W-10W-20W-Watts-Solar-Panel-12V-Off-Grid-Battery-Charger-for-Car-RV-Boat/122927133972?hash=item1c9f073514:m:mZjbJTB8gGagqDA0DGeTAsQ&var=423375671084

[B and C]

Since I am not able to take my van out for regular exercising (I do start it and let it run when I exercise the generator once a month), I got a 10 watt solar panel and connected it through a small 3 amp pwm charge controller:
https://www.amazon.com/gp/product/B00PFG56ZS/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1

This keeps the starter battery topped off and I don't have to worry about overvoltage. I also put one on my Geo and my 2 on my motorcycle trailer. I put mine on the windshield and let the wiper blade hold it up. It hasn't blown off yet.

[Flying kurbmaster]

My charge controller (BlueSky mppt 30 or something like that) has that option built in, I can run a set of wires to my start battery and it trickle charges automatically, when it is charged I think it switches itself off, I still haven’t done this yet but will one of these days as the controller can do this. I also have a marine Battery switch, that has the option of one battery two or both which I used before getting this fancy charge controller and can still use. Which means if my house battery ran dead I could use my starter battery for emergency lighting, or if my starter battery ran dead I could boost it by turning the switch to both, I also think I could charge the starter battery by switching to both from the panels. I can also charge both, or one at a time from the alternator while driving by selecting from the switch.

[Roadtripp]

BT....Did you get it charged enough and started? Must have.
I’ve been looking at some small charge controllers. They are inexpensive. Morningstar makes a 4 amp PWM (pulse width modulation) controller. More fancy is the Morningstar Sunsaver Duo 25 amp controller that I’m trying in my old motorhome for the original 12 volt house battery and 12 volt generator battery (there is no Motorhome starter battery in it as it’s only moved every few years). The Duo controller current can be adjusted using dip switches to 90%:10% or 50%:50% charge to the two separate batteries. Using a computer it can be set to any ratio.
A nice little meter, Morningstar RM-1, is available for the Duo controller showing the voltage and current to both batteries. The Duo also has temperature compensation for the charge voltage.