Someone previously told me that the amplifiers should only be pulling about 10.4A peak power but that was worked out by dividing the wattage of the boost converter with voltage of the output, I don't know if that would still be the case with just a 48v battery instead. I saw a review video for one of the amplifiers that seems to indicate that at 45v I'd be looking at a continuous 5A for the wattage I need.
Depending on the amp design, it may draw more current at a lower voltage to give the same wattage, but some will draw less current at a lower voltage for less wattage, because of the resistance of the circuits, speakers, etc.
You can test this if you like, using a simple test signal pattern that you can use repeatedly to make the same test each time. Test at one voltage, then another, while monitoring both votlage and current into the amp.
I'm a bit confused by the different voltage ratings and what they actually mean, if 48v is the nominal voltage does that mean that a fully charged battery pack would be putting out too much voltage for the amplifiers maximum which is 48v, would I be better off with a 1 or 2 cell smaller pack to avoid damaging the amplifiers at full charge?
If the amps have a hard voltage limit of 48v, then to ensure you don't exceed that, then you can either not charge fully, or use less cells. Not charging fully won't lose you much capacity (a few percent or less), while using less cells loses you significant capacity.
An LFP cell is around 3-3.2v for most of it's discharge curve: Here's a randomly-found discharge curve of one version of a headway cell. Each colored curve is the voltage over time/capacity at a different current (1c is 10A, 2C is 20A, 3c is 30A, etc., for this 10Ah cell)
It shows that at 1C (10A for a 10Ah cell) it would give you about 3.1-3.2v per cell for about half of it's capacity range (the first 5Ah or so). Then it starts to curve down in voltage more and more, staying above 3v for another quarter or so of it's capacity, then dropping faster and faster to empty around 2.5v (it's really empty at 2v, but there's not even a few hundred mAh between those points).
What that means is that for a 48v pack, if you assume 3.4v full charge (instead of 3.65) (it will sag down under load, probably to about 3.2v), then 48 / 3.4v = 14s, that gives 47.6v max. If you assume 2.5v empty, then 14 x 2.5v = 35v minimum. You'd probably get about 9Ah or more out of the 10Ah these specific cells could potentially give.
Different cell brands / models have different curves, so you can reference their spec sheets for this if you want to see what it is for any specific cell. But you can guesstimate that most LFP cells will give about 90%+ of their rated capacity if you use them within the 2.5-3.4v charge range.
If your amp would fail at 48.1v, you might want more margin than just half a volt of safety, though, and maybe go for 13s at 3.4v/cell max.
If you're not using a BMS on the pack, then you may want to periodically check them at either the empty or full state (not both) to see if they are all equal, and if not, either drain the high ones with a resistance or fill the low ones with a single-cell charger till they are.
If you will use a BMS on them, then you'll need one that is programmable for HVC, LVC, and balancing points so it will work with the "nonstandard" max charge and min discharge points.
ambientvoid said:
Sorry for the late reply, I don't know why but I didn't get any email notification of replies.
Many providers autofilter out forum notifications because so many of them from the same domain pass thru their servers so it looks like spam. This is done before it gets to your inbox, so it doesn't even show up as spam in your email, they just never get sent anywhere.
If you find them in your spam/junk folder you can setup a whitelist for them in your email options.
