Trickle charge battery with solar

[jblc]

[ I searched around online, but didn't see a direct answer on how to safely do this. Also, didn't see answers to some below questions. ]

I already have an 80 W CIGS solar panel installed on my camper shell, charging a power pack. I'm hoping to use it to continuously trickle charge the vehicle battery.

What's the preferred method to safely bring power to the battery, without risk of shorts, minimizing damage to components in case of shorts, etc?
Specifically,
(a) Should a separate ground wire be routed directly to the battery, or local ground near the battery? Or is it better to only run a + wire, and instead connect the - output to ground near the back of the vehicle where the panel's located? (since the battery "-" is already connected to ground)
(b) should the charge controller be closer to the battery, or the panel?


Two options so far:

1) solar panel -->
charge controller -->
wires under car, fused on both ends of both wires (unless needing to only route +) -->
battery

Or,
2) solar panel -->
wires under car, fused on both ends of both wires (unless needing to only route +) -->
charge controller -->
battery

Or something else?

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[JesseS]

I would install a SAE pigtail on the battery, hooking the neg wire to ground and not the battery so the BMS can manage the power. Then just run this to the solar controller as long as it is set to charge gel-cell or flooded batteries (whichever you have). Running the wire from the shell top to the battery is your option, under, thru, or loose coil hooked up whenever you are stationary.
As for the wire if going under the truck, use 10ga in a wire chase and follow the OEM wire loom up to the battery, that would be my preference.
As the panel isn't grounded you will run both to the controller, then controller out to battery Pos+ and ground the Neg close to the battery but not on it. Only need to fuse the Pos+ at the controller output. The panel only puts out 9A but the controller could charge at up to 14-18 if your battery is low so I would fuse the output at 20A.

 

[jblc]

then controller out to battery Pos+ and ground the Neg close to the battery but not on it.

Thanks for the thoughts . Why does the ground need to be close to the battery? Wouldn't the BMS already detect the appropriate current, regardless of where on the ground it was attached?

 

[JesseS]

Thanks for the thoughts . Why does the ground need to be close to the battery? Wouldn't the BMS already detect the appropriate current, regardless of where on the ground it was attached?

More than likely but there could be a possible issue depending on the sensitivity of the BMS. If you put the controller in the engine bay you will need to run both wires in any case, not sure if your controller is on the back of the panel or remote mounted. Guess I am just old school, I like to see both terminals of a circuit, I am doing the diodes and wiring to tow the Ranger, and I didn't know it had a BMS,(had to look it up) the solar install I did on my RV uses LiFePo4 batteries with the BMS is inside the cell pack.

 

[jblc]

If you put the controller in the engine bay you will need to run both wires in any case, not sure if your controller is on the back of the panel or remote mounted.

Thanks. Yeah, this is the question that I was wondering in the two scenarios I posted about:

is there a difference between
1) connecting solar ground to the chassis near the panel, and placing the charge controller remotely (eg engine bay) while running just the + wire of the panel to the charge controller. (Obviously, charge controller would get "-" from the chassis nearby)

OR

2) place the controller near the panel in the back, connect controller output "-" to ground, and only run the "+" charge controller output to the battery (since the battery is already connected to gnd)

 

[JesseS]

Thanks. Yeah, this is the question that I was wondering in the two scenarios I posted about:

is there a difference between
1) connecting solar ground to the chassis near the panel, and placing the charge controller remotely (eg engine bay) while running just the + wire of the panel to the charge controller. (Obviously, charge controller would get "-" from the chassis nearby)

OR

2) place the controller near the panel in the back, connect controller output "-" to ground, and only run the "+" charge controller output to the battery (since the battery is already connected to gnd)

Do not ground the solar panel neg , both the Pos and Neg must go to the controller, depending on the panel the output can be between 19-35VDC, and the controller steps this down to 13.8-14.4 depending on battery type selected while at the same time upping the amps. The neg output from the controller to the battery can be connected to chassis ground and the pos to battery
#2 above is your best option.

 

[jblc]

Do not ground the solar panel neg , both the Pos and Neg must go to the controller, depending on the panel the output can be between 19-35VDC

Thanks for the continued thoughts -- I'll likely go option #2.

However, why does a higher voltage mean they shouldn't share a common ground? Eg grounding the solar "-". Ground is independent of the + voltage value.
Eg it's okay to share grounds for anything DC: +5, -12, +24, +48 V; the ground is just the return path. (These are just random examples)

 

[XLT_TREMOR]

2) place the controller near the panel in the back, connect controller output "-" to ground, and only run the "+" charge controller output to the battery (since the battery is already connected to gnd)

I’d do this option 2. With a fuse in the pos side battery pigtail, and another fuse after the controller. Both are needed to prevent shorts when the solar isn’t hooked up.

However, why does a higher voltage mean they shouldn't share a common ground? Eg grounding the solar "-". Ground is independent of the + voltage value.
Eg it's okay to share grounds for anything DC: +5, -12, +24, +48 V; the ground is just the return path. (These are just random examples)

I believe the issue is with the controller. Not sure how it would regulate the panel output without having separate grounds for input/output.

I’m interested in doing something similar. I currently do maintenance solar charging from the interior via the OBDII port using panels totaling about 40W. Output is low enough that it doesn’t need a controller. I haven’t seen more than 13.2V when hooked up in full sun. I’d normally use the 12v cig power ports, but they don’t remain hot when the engine isn’t running like the OBD port. Works okay when I can park facing the sun, but I think I want something on the roof for times that I can’t.

 

[jblc]

To update, i ended up connecting a Rich Solar 20A MPPT controller: the battery output going to the car battery.

HOWEVER, when I checked with Rich Solar to verify that the controller can withstand startup voltage spikes from the alternator, they said to NOT connect a vehicle battery to the charge controller -- only a Deep Cycle battery should be used.

Does anyone know more about this? What's the danger of connecting to a normal AGM battery?

 

[HDEO]

To update, i ended up connecting a Rich Solar 20A MPPT controller: the battery output going to the car battery.

HOWEVER, when I checked with Rich Solar to verify that the controller can withstand startup voltage spikes from the alternator, they said to NOT connect a vehicle battery to the charge controller -- only a Deep Cycle battery should be used.

Does anyone know more about this? What's the danger of connecting to a normal AGM battery?

I suspect you will quickly damage the car battery. It’s not designed to power accessories like a deep cycle battery is. But maybe that’s not your plan?

https://auto.howstuffworks.com/question219.htm

 

[jblc]

I suspect you will quickly damage the car battery. It’s not designed to power accessories like a deep cycle battery is. But maybe that’s not your plan?

https://auto.howstuffworks.com/question219.htm

Thanks. I'm not running anything off of the car battery. I'm only using the solar charge controller to maintain normal operating voltage, since my car sits for a while at a time without running. The battery voltage continues to drop low pretty quickly (as most on this forum can attest, since the Ranger has a high quiescent current)

Is charging a car battery with a charge controller not advised?

 

[HDEO]

Thanks. I'm not running anything off of the car battery. I'm only using the solar charge controller to maintain normal operating voltage, since my car sits for a while at a time without running. The battery voltage continues to drop low pretty quickly (as most on this forum can attest, since the Ranger has a high quiescent current)

Is charging a car battery with a charge controller not advised?

I don’t know a lot about this but I have built an electric bike and have a couple of Goal Zero camping batteries. So I have some experience with batteries. I know that the charging profile which is the rate at which power is put back into the battery by the charger is very specific to the battery chemistry. So I’d be careful about using a charger that is designed for a Lithium battery on a nickel metal hydride or lead acid battery for example. It’s possible to have a fire or explosion and you sure don’t want that.

 

[jblc]

So I’d be careful about using a charger that is designed for a Lithium battery

The charge controller is set to sealed lead acid battery, so it's charging using the right chemistry settings.

 

[XLT_TREMOR]

To update, i ended up connecting a Rich Solar 20A MPPT controller: the battery output going to the car battery.

HOWEVER, when I checked with Rich Solar to verify that the controller can withstand startup voltage spikes from the alternator, they said to NOT connect a vehicle battery to the charge controller -- only a Deep Cycle battery should be used.

Does anyone know more about this? What's the danger of connecting to a normal AGM battery?

I think their recommendation is overly cautious. Their own specs say it’s fine up to 32v on the battery side. Your alternator will never spike that high. If I were concerned about it, I would just put a switch or diode in the positive side between the controller and battery.

Their own specs say that it works on flooded, gel, and sealed(which the AGM is) and are all lead acid…so not sure why they would have a concern.

As for the different chemistries…yes, I would never charge anything lead acid with a charger for any lithium or other battery chemistry. And I normally wouldn’t choose to use an AGM or gel setting on a regular flooded starter battery. But it’s not a big deal to use almost any 12v lead acid charger on any 12v lead acid battery, aside from using one that is old school and simply too high output for the target battery.

My suggestion is to use a multimeter and check the charging algorithm with the system hooked up in the full sun using a multimeter. Record the voltage at regular intervals and see what it does. I’ve done that for every charger I’ve ever used so I know exactly what it’s doing, unless it has its own display or was low tech in the past with an ammeter.

FWIW, I use various panels hooked up directly to the batteries for several years now without adverse effects. Motorcycle sizes up to 800CCA. All of the panels are in the 18v-22v range full-sun open circuit, but all of them drop down to just above the battery voltage, and I have no problems keeping everything in the fleet topped off between 12.80v and 13.12v year round. All coincidentally AGM now since I traded an Explorer for the Ranger.

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