Aircraft batteries

[Snagger]

14 hours ago, Ed Poore said:

It's rather more critical than that - lithium batteries don't like being outside a quite narrow temperature range, something like 0-40°C if I recall, to even operate safely. I think they require even tighter constraints if they're to be operating optimally. Basically the lead acid is there to start the main battery pack, if it's too cold then it warms it up - if it's too hot then it can cool it down.

Thinking about it I don't know if it has to be always on or whether that's just for when power is being pulled out of the battery pack.

The “traction battery” will typically be 400v, but are now increasingly commonly 800v.  They are used to keep the 12v battery topped up while in use, but I understand that they can disconnect from the 12v battery when parked, so it is still possible for the 12v battery to become discharged even if the traction battery holds a reasonable charge.  As you said, the 12v battery manages all the electronics, including the traction battery charger, so if you have a flat 12v battery, you probably can’t charge the traction battery either.

Most EV reaction batteries have temperature regulation.  Nissan ignored it completely in the first generation Leaf, beyond limiting charge or discharge rates, and consequently they had much worse battery degradation than other vehicles.  Their second generation has battery heating pads, not much different to seat or wing mirror heaters, to precondition the batteries prior to charging them in cold conditions, but they still didn’t have active cooling, and not pr do some other cheaper EVs.  They rely on conduction to the airflow, which isn’t enough in hot climates at high charge or discharge rates.  I no it likely the heater pads would be powered by the 12v battery - the 12v would power the traction battery charger and would command the battery heaters to warm up the traction battery before it allows a charge.  The mass to be heated would rapidly drain the 12v battery.  As for driving in cold climates, I very much doubt the 12v would heat the batteries then either, though the ECUs may command the heaters to use some traction battery power, depending on whether the energy consumed by the heaters is less or more than the extra charge available from the warmer batteries.  I think they mostly rely on heat generated by the discharge itself.

[elbekko]

36 minutes ago, Snagger said:

They are used to keep the 12v battery topped up while in use, but I understand that they can disconnect from the 12v battery when parke

That's how it is on my PHEV, only charging when then ignition is on (and the voltage drops low enough).

[JohnnoK]

On 6/7/2024 at 6:14 PM, Av8or said:

Unless you're talking about transport category aircraft - in which case the batteries are going to be far, far too big for usage in automotive applications, aircraft batteries borrow technology for the automotive world. That's where all the innovation exists and isn't stifled by bureaucracy. 

Originally my plane was certified with a big Gill lead-acid battery in the tail underneath the baggage area. In more recent decades it was allowable to get a Supplemental Type Certificate (STC) to put a much smaller AGM battery on the firewall. This has the advantage of being lighter weight, removing a significant amount of heavy-gauge wire, better starting, and the engine heater will keep the battery warm in arctic climates. Picture attached with the battery on the left side of my firewall (Right side, WRT to the photo). This battery costs me $200, which for plane parts is shockingly cheap.

https://www.aircraftspruce.com/catalog/elpages/odysseydry7.php

 

How does that STC affect your CofG shift? Is it to your advantage or did you need to ballast it?

A previous employer I worked for used the sealed lead acids in almost all the choppers that it was STCd for, and they were great.... we had a small plug-in conditioner that we used to check the status every 3 months, a topping charge if needed at 6 months and replace at 12 months. Best of all, they were not Dangerous Goods due to being sealed and spill proof, so getting them to us in Venezuela/Burma/Sudan/Libya and similar dumps wasn't extortionately expensive.

[Snagger]

I’d imagine the small CoG shift forward would be minor, and a forward shift increases dynamic stability, so should be a very small issue if it comes up at all.  Mods like this must be on a list of existing approvals, I’d think, as it must be commonplace nowadays.

[Av8or]

On 6/9/2024 at 1:44 AM, JohnnoK said:

How does that STC affect your CofG shift? Is it to your advantage or did you need to ballast it?

My Cessna 180 has a pretty nose forward CG to begin with. You have to keep in mind the plane is designed for carrying moose carcass, oil drums and other utility roles in Alaska, so it's built with the idea that the cargo area is going to be loaded pretty heavily. I didn't have to ballast, but this did shift my CG further forward, however; the weight savings and other secondary benefits are more than worthwhile.