Having some fun thinking about a DC-only (for now) solar+alternator build for a compact car. Hashing out some thoughts here in case anyone can help.
I have found three devices that might be all-in-on solutions for smart switching between alternator and solar charging, while also keeping the starter battery topped off:
- CTEK D250SA, https://www.amazon.com/CTEK-40-186-Automatic-Battery-Charger/dp/B005LBCVL4
- Renogy DCC50S, https://www.renogy.com/dcc50s-12v-50a-dc-dc-on-board-battery-charger-with-mppt/
- REDARC BCDC1225D, https://redarcelectronics.com/products/dual-input-25a-in-vehicle-dc-battery-charger
The Renogy and REDARC both explicitly support lithium batteries, whereas the CTEK only explicitly supports lead acid. I've already decided I will use only lithium batteries for such a project, and I'm not sure if the lead acid controller will work efficiently/correctly on a lithium battery... The Amazon Q/A has a question asking "Can you use this for a lithium battery setup?" to which the reply is "No, CTEK is clear that these are for lead acid type batteries only." So CTEK might be out of running.
The CTEK and REDARC have smaller output at 20A and 25A versus the Renogy at 50A, and probably the smaller output is better suited to the compact car alternator that the charge controller would be used with (although I might be wrong about higher output negatively affecting the car alternator lifespan). The Q/A on the Renogy website has a question asking "Truck limit of 30 amp thru trailer plug. Is there a way to avoid blowing truck fuses in charging the truck battery/or using truck to charge trailer solar battery bank?" to which the reply is "Thank you for contacting Renogy, currently it can only be limited to about 12%".
Does "limited to about 12%" mean the Renogy can be scaled down to 6A of output? If so, the Renogy might be more flexible in this regard which would be good when moving the system to a larger vehicle. However, it is possible what is meant is that output can only be scaled down to 44A, or 12% less than the full 50A. Not sure?
As for service battery and panel size, I'm really not sure if these specs are overkill for my usage, but the price point is fine: I'm planning to power one 100ah lithium battery, starting with one 100W solar panel, scaling up to a maximum of two 100W panels for a total of 200W if the one 100W panel is not enough to reach full charge.
The load on the service battery will be the occasional RC lipo battery charge (couple of 6s and 3s packs), running a 12v projector directly off DC, and an always recording dash cam. I might find some other things I'd like to power in the future and assume I have some headroom because I guesstimate the dash cam to draw ~5ah, which I assume won't overly deplete the battery during overnight.
My area has great sun during the day into the late afternoon but also cold winters so I guess I will need a lithium battery that has a heating element or I will need to build a heated box. I'm not sure if the heated box would be warm enough to also allow storing RC batteries in the car in the winter?
Adding a pure sine inverter at a later date (if I eventually purchase an electric skateboard) would allow me to charge AC using solar as well which would be nice, although I'm not sure if the 100ah battery would be enough to fully charge a skateboard; I'm really not familiar with doing these energy calculations.
I haven't seen much about the solar+alternator charge controllers and am not sure which battery to get. I also get the impression from some of the YouTube videos that perhaps charging off the alternator is frowned upon, but it is not clear if that's because it damages the alternator (which I hope the expensive all-in-one systems do not) or we just prefer full solar, or if I just got the wrong impression?
I have found three devices that might be all-in-on solutions for smart switching between alternator and solar charging, while also keeping the starter battery topped off:
- CTEK D250SA, https://www.amazon.com/CTEK-40-186-Automatic-Battery-Charger/dp/B005LBCVL4
- Renogy DCC50S, https://www.renogy.com/dcc50s-12v-50a-dc-dc-on-board-battery-charger-with-mppt/
- REDARC BCDC1225D, https://redarcelectronics.com/products/dual-input-25a-in-vehicle-dc-battery-charger
The Renogy and REDARC both explicitly support lithium batteries, whereas the CTEK only explicitly supports lead acid. I've already decided I will use only lithium batteries for such a project, and I'm not sure if the lead acid controller will work efficiently/correctly on a lithium battery... The Amazon Q/A has a question asking "Can you use this for a lithium battery setup?" to which the reply is "No, CTEK is clear that these are for lead acid type batteries only." So CTEK might be out of running.
The CTEK and REDARC have smaller output at 20A and 25A versus the Renogy at 50A, and probably the smaller output is better suited to the compact car alternator that the charge controller would be used with (although I might be wrong about higher output negatively affecting the car alternator lifespan). The Q/A on the Renogy website has a question asking "Truck limit of 30 amp thru trailer plug. Is there a way to avoid blowing truck fuses in charging the truck battery/or using truck to charge trailer solar battery bank?" to which the reply is "Thank you for contacting Renogy, currently it can only be limited to about 12%".
Does "limited to about 12%" mean the Renogy can be scaled down to 6A of output? If so, the Renogy might be more flexible in this regard which would be good when moving the system to a larger vehicle. However, it is possible what is meant is that output can only be scaled down to 44A, or 12% less than the full 50A. Not sure?
As for service battery and panel size, I'm really not sure if these specs are overkill for my usage, but the price point is fine: I'm planning to power one 100ah lithium battery, starting with one 100W solar panel, scaling up to a maximum of two 100W panels for a total of 200W if the one 100W panel is not enough to reach full charge.
The load on the service battery will be the occasional RC lipo battery charge (couple of 6s and 3s packs), running a 12v projector directly off DC, and an always recording dash cam. I might find some other things I'd like to power in the future and assume I have some headroom because I guesstimate the dash cam to draw ~5ah, which I assume won't overly deplete the battery during overnight.
My area has great sun during the day into the late afternoon but also cold winters so I guess I will need a lithium battery that has a heating element or I will need to build a heated box. I'm not sure if the heated box would be warm enough to also allow storing RC batteries in the car in the winter?
Adding a pure sine inverter at a later date (if I eventually purchase an electric skateboard) would allow me to charge AC using solar as well which would be nice, although I'm not sure if the 100ah battery would be enough to fully charge a skateboard; I'm really not familiar with doing these energy calculations.
I haven't seen much about the solar+alternator charge controllers and am not sure which battery to get. I also get the impression from some of the YouTube videos that perhaps charging off the alternator is frowned upon, but it is not clear if that's because it damages the alternator (which I hope the expensive all-in-one systems do not) or we just prefer full solar, or if I just got the wrong impression?
