24v panel 12v battery car setup

Re: 24v panel 12v battery car setup

The largest jump-start battery pack I've seen (this Peak 900 battery) contains an 18Ah battery. Since the battery pack includes USB and 12VDC outlets, I would imagine that the plates are marginally thicker than those on a regular SLI battery. I still wouldn't want to use more than about 4Ah of its capacity before recharging.

Re: 24v panel 12v battery car setup

kcm1 wrote: »

.. I believe the storage capacity of a decent jumper would be sufficient for my small camping power needs (charging electronics, fan, hotpot, heated throw, nothing more than about 150W), and also serve as an emergency jump / air compressor.

Inside those jumper packs are generic general-purpose agm's. The largest I've seen are the Stanley units, inside of which are 18ah. Most are not user serviceable for battery swapouts, although I did modify mine with a 22ah agm since it was the same size.

These batteries are limited to 0.3C charge current, which for an 18ah agm means about 5.4A constant charge current maximum. If you were able to open your jumper, you may see this rating. So what we are talking about is an 80W nominal 12v panel, with a small pwm controller, like a Morningstar SunSaver 6A type. Connections can go straight to the battery through the clamps, bypassing the relatively poor cigarette lighter jacks. Of course you have to turn the clamps on first, attach the controller, and the panel last. Above all, you have to be SAFE doing this to prevent an inadvertent short of the clamps.

The problem is the battery size and what you want to do. Consider that the 18ah battery has a watthour rating of:

12v * 18Ah = 216wh available. BUT since we don't want to draw more than half of a battery's capacity, we cut that value in half. That means you really only have 108wh to play with on a daily basis.

So you are going to have to make 108wh last for your nightly duration. A 150 watt load is not going to last very long - much less than an hour. Note that the 400w inverter is a *surge* rating, and not a continuous draw setup. It is also a modified-sine-wave type (MSW) and not a pure-sine-wave (psw) and some things will not work well, run slow, or overheat.

Tip: depending on how well built / isolated the USB circuitry is, if you overload them, it can take out the logic of the entire jumper pack and render it useless. Most are rated at the standard 500ma standard, so charging modern devices will be real slow, or the usb circuit blows. Better to use an external mobile 12V > 5v usb adapter, like some Anker units plugged into the cigarette lighter jack instead.

Basically, even with a small system, you still have to very carefully measure your actual loads over time. In this case, will 108wh be enough daily. The other side of the coin is your solar insolation. Do you have 4 hours of solar-insolation where you are when camping? These differ from mere sunrise to sunset hours and need to be looked up online. For instance, let's say you draw your battery to half of it's capacity - now you have to replenish 9ah. Can you do that in time with an 80w panel (near max limit)?

Let's see:
9ah / 4.5a solar * 1.78 fudge factoring = 3.56 hours. Let's make that 4. You just might make it provided you do have 4 hours where you are going daily if you discharge that far.

The jump-starters are fun / ok IF you do all your homework up front first, otherwise you'll be wasting money. Get out the multimeters, measure your dc current draw and total it over time, in addition to measuring actual wattage draw of AC devices with something like a Kill-A-Watt meter. You'll also want to know the real ah capacity of the internal jumper battery pack.

Most jumper-pack solar installs are just winging it, and it ends back up in the garage on the provided ac charger because in reality the capacity is just too small for what many think they can really handle.