On Wednesday, November 14, 2018 at 2:56:35 PM UTC-5, kinsell wrote:
On 11/14/18 9:03 AM, moshe... wrote:
On Tuesday, November 13, 2018 at 11:11:52 PM UTC-5, kinsell wrote:
On 11/13/18 6:08 PM, bruce... wrote:
Mark, When K2 was fairly new on the market I contacted them asking if Battery Tender Jr. is okay and safe, they replied that it is perfectly okay and nearly the same as their charger. I also contacted Battery Tender Jr. with the reverse question and they said the BTJr is fine for LiFePO4. I used the BTJr for years on my K2 with no issues. They're about $25 on internet sites.


Have you measured the amount of charge you're getting into the K2's? It
will be considerably less than the rated amount due to using a lead-acid
charger.

Also, if K2 has cell balancing capability, it won't be used because your
Battery Tender doesn't put out enough voltage to make it work.

Many simple lead-acid chargers reach up to around 14.2-14.8 volts. That voltage would suffice to charge an LFP battery to well above 90% capacity if it stays there for a while. If it quickly shifts to "float" at 13.5V or so then it won't do well in charging LFP. So simpler is better in this case. Measure what your charger does. And disconnect it after several hours, don't leave it on "float".


Hate to break this to you, but at $24, the Battery Tender Junior is one
of the cheapest chargers on the market, and is fully featured with a
float mode.

14.2 volts wouldn't begin to charge an LFP to "well over 90%" as you
claim. If you found a charger that delivers 14.8 volts under load, then
it would overcharge an SLA and would be considered defective.

If you're going to spend big bucks for an LFP, you ought to get a proper
charger for it. Still waiting to hear just how much charge the K2's got
in them from a BTJ.

-Dave

That's the conventional wisdom, but see experimental results he
https://www.powerstream.com/lithium-...ge-voltage.htm
- well above 90% capacity even at a bit lower than 14V!

A cheap dumb 14.x volt fixed-voltage source with limited current output (and perhaps aided by the battery's BMS) would charge an LFP just fine. I'm not saying that's the ideal charger, but in a pinch it would work well enough. I am not happy with the several chargers I have that push SLAs well above 14V (even above 15V), but they may be handy for LFPs.