Lipo battery options

[tomarnold]

I am finding that the 12v lead acid battery just isn't enough to start my Simonini Mini 2. Not enough power there. If I connect it with jump leads to my car, it starts instantly.

I flew with a friend at the weekend who used a lipo battery pack to jump start it. We made a little connector using xt60 connectors and a couple of leads connected to the battery terminals. We then connected it, started the motor, and immediately disconnected the lipo and left it with our kit on the ground while we flew. This was SO effective I thought I must buy myself a lipo battery and charger. 

My question is, do you think this is a safe enough option? I don't intend to fly with the lipo, I'll just connect it to jump start the motor then leave it behind. Or alternatively I could disconnect it after the motor starts then carry it in a fireproof bag velcroed to my frame. 

My Simo has in flight charging, but I'm guessing that having the lipo connected to the main battery for literally a second or two after starting isn't going to do any harm. Or am I wrong in thinking this? If so, can anybody help me with how to disconnect the charging circuit? 

I'm looking at buying a 1500mah 60c 4s lipo, as I will only use it for 1 start then charge it at home. 

[AndyB]

All AC  elec machines fly with a Lipo. It is kept in a small fire-proof bag. They only ever go up in flames when charging (incorrectly) or sudden short circuit - although the latter often results in a resounding nothing. I have driven nails through old packs to ensure they are dead....and never managed to get a decent fire, just a few small flames twice. You CANNOT charge them in flight, but they last so long, you never need to. I use a small 1000 mah pack (weighs nothing!) and it lasts me more than 10 flights, with multiple starts in flight.

[steelmesh]

Most LiPos are rated for 3.7V/3.8V nominal, which makes it challenging to add to a lead acid charging system.  I think the paramotor manufacturers are selling are LiFePO4 lithiums, which have a lower nominal voltage at 3.3V and are more tolerant of abuse (aka safer) when added to a lead acid charging system.

With LiPos you are required to run a BMS to ensure safe operation, you cannot ensure safe operation of a LiPo battery without a BMS.  The bandaid is to use a balance charger in balance charging mode which will catch a bad cell (and prevent charging) before the battery is put back into service.  LiPos are most dangerous when they are fully charged, this is when they will release the most energy during a 'rapid disassembly' event.  A reliable way to set off a lipo pack is to overdischarge it then puncture it. Most of the gas released is very flammable which can reach 1000C at the source if ignited.

Edited October 28, 2019 by steelmesh

[Adam Ferguson]

Just my 2 cents but as Steelmesh if your current draw will allow I would always go for a LiFe over a LiPo. Yes they do have a lower nominal voltage but they are a much more stable chemistry making them a lot more forgiving for both charge and discharge. Also they have a much lower self discharge rate meaning you don't have to put them to storage voltage if you want to store you kit up for more than a month or two. 

[rhys]

Has anyone considered using on of the new jump start packs for cars bikes etc  they use litium batteries at12v output high amps   cheeper than lipo made for high draw rate to boost car starts upto 6.0l engine size ? Whats ya thoughts 

[Nikolatesla]

I personally don't ever fly in our motorised garden chairs with high energy battery power that could go wrong .

But if you must ,find a place where the battery pack can burn and not be life threatening . A firewall of bespoke design is the best you can do . I don't fly a paramotor but off to one side shielded from the fueltank.?