Portable Generator Power Bank Station Solar Charger Battery Backup 70200mAh 100W $205.39
Trying to gauge whether these eBay units really do have 70000 mah batteries when named brands are either 1/4 of the capacity for the same price or 3 times more expensive.
I've been looking for one for a while what has pd and 12v output. I don't need 240v, but I need 12v 8amp so pd doesn't cut it. (And ideally over 400wh/ 50ah). Any suggestions?
Crikey!
If it is on eBay it will be cheap Chinese rubbish - save your money.
Ebay- the worst market in the world to buy high-energy density storage devices. Worse than Aliexpress, worse than Taobao.
With these sorts of things like portable batteries n such don't go and cheap out on un-branded rubbish from ebay or aliexpress.
The hazards for it not being compliant or safe puts not just you but the lives of others at risk. Just look at those cheap e-scooters n such with lithium ion batteries. Super dangerous when it goes into thermal runaway and hard to extinguish and contain.
The 12v output seems to be just a standard DC power socket, which you'd be lucky to draw 5A from safely. So, 60 watts instead of the 100 watts (ie 8A) that they say is available (and the 50A you seem to be looking for).
As for the 70Ah rating, that has to be pure fiction. What these manufacturers do is simply add up the amp/hour rating of all of the cells in the unit regardless of how they are wired. That's not math, that's imagination.
Let's assume that this device is filled with 18650 cells. The highest real capacity available for an 18650 cell is 3.6Ah. So, 70/3.6 is about 20 cells. That's not impossible. However, to get that 70A, you'd need to put all of the cells in parallel, which would only give you the same output voltage as a single cell. So, that's not realistic.
So, let's assume that the 20 cells are wired up to provide about 12v. Let's also be generous and say that three cells in series gives you 12v, but because they're in series, the Ah rating stays the same as a single cell. So, you'd have seven groups of three cells, but seven times 3.6Ah is only about 25Ah. To get 70Ah at 12v, you'd need nearly three times as many cells (in round figures), let's say 57 to keep it a multiple of three. Would that many cells fit in the case? I can't see any dimensions in the listing.
Rather than premium 3.6Ah cells, more likely, the cells in this device would be 2.6Ah, and maybe even lower. And four cells is a better idea than three to get about 12v output for a useful time. I think you can see where this is going.
And if there's any voltage regulation or voltage conversion, more power will be thrown away in heat, further reducing the device's real Ah rating. The numbers just don't add up, as far as I can see.
A cheapie 12v 50Ah lithium battery is about $350 +/- you will also require a charger so probably another $150 +/-. A 12v AGM battery @50Ah is about $120 plus charger (another) $80.
If you go lead acid you save money but gain weight. If you're not moving the battery around then there are savings.
I assume you want to power the 12v device continuously for about 6 hours. Remember that lead acid batteries are less forgiving of deep discharge so you may need a larger one.
I personally wouldn't get any power bank/battery product from eBay after I had a car jump starter I bought from ebay exploded in front of my face and started burning. Luckily no one was hurt and I had a fire extinguisher right next to me at the time. Scared the shit out of me though.