The Peak Jump Start

That build brings a tear to my eye. Used to do the same thing, but stuffed them with pure-lead Odyssey agm's.

Storing at full with LFP and a compromise? I take the more practical approach that I tell my neighbors to do with their lithium tools rather than shoot for a specific level:

After a full charge, just get them out of the upper knee. Done.

As for neighbors tools, which can also apply here (albeit being a different li chemistry), I'd just tell them that leaving them on full charge is fine during the season you are actually using them like at least once a week or every other week.

If you aren't using them, or when the season is over, charge them up full for the last time, and then pull the trigger for only a minute, whether it's a drill, leaf blower, whatever. Just run them doing nothing for a minute and then store away for next season.

When I started talking about measuring down to specific values, eyes would gloss over. So the "just pull the trigger for a minute" after your last full charge seems to work on a more practical level...

Back in post #12 I learned that I shouldn’t be storing it fully charged, so after that I didn’t charge it up until I knew I’d need it for the next day or at the start of hurricane season. Which is to say since 2020 spring I’ve been a bit careless about it. Last April I discovered I’d let the SoC get down to about 10% (oops… I’m a bad owner). In May I tested and saw 356.3 Wh, so a ~1.5% capacity loss.

Starting voltage was 13V. Currently pulling a sedate 150 watts and hit 11V at 345.6 Wh, so a 3% loss from May, and a 4.5% loss altogether for two years. 3% seems like a fairly big hit for 6 months. Possibly experimental error?

Discharge Test!

Haven't had any need to use this after my last test, so it's just been sitting waiting.

Says it's at 13.28V. Hmmm, that's suspicious. 3.2V is nominal, so 13.28 / 4 = 3.32. The range is 3.5 to 2.5V, so the self-discharge was pretty small. Possibly I used it/charged it and forgot about it.

Well, let’s charge it and run a capacity test.



Charged it all the way to 14V (3.5V/cell), then set it to drain at about 8.6 amps and 110 watts. 3 years ago, when new, it was 362 Wh. Thie discharge rate is about .25C. The inverter cut out at 11V (2.75V cells).



So, plotting the last few tests:
So 2.5 years and lost about 5% capacity.

That's awesome. Thanks for doing a followup test! Yeah, very little self-discharge.

In the field, I've been fooled by new cells (or those that saw very little use), and left in storage. Not fully charged mind you. However, I've seen instances of a very weak surface charge holding the terminal voltage much higher than expected a year or so later regardless.

Once a very small load was placed on it for just a few seconds, the terminal voltage dropped to what was expected and measured stable at that voltage 12 hours later. I *think*, but have not confirmed, that in the case of very new cells, that if left alone for long periods of time, a surface charge can develop either stopping what would be deemed normal discharge voltage, or raising it even - like after a year or more of sitting in the corner.

I also use one of those devices at times. Very handy. However I'd be tempted to use your own voltmeter and repeat the test again under the same parameters. Probably very very close to what you have now, but since you got the gear out ....

Thanks again for doing the test. It's always nice to see followups.

You don't use them all the time?

I have ALL my phone and small electronics running off mine. They usually last 2 or 3 days depending on if the wife charges her phones on it too...
I rotate them on the solar charger I have in the back of the house.

I'm still tinkering with my 1800Wh beast though... that much LFP is HEAVY!

Heh, that's one of the unsung beauties about LFP - much easier to reconfigure as one ages.

Unlike lead acid, where once you place a bank in it's home, that's where it stays. 6 years later you are 6 years older. Suddenly you can't man-handle those 8D's around like you used to.

Peak Jumpstart Breaks!

Inside the jumpstart box it has a little walwart (AC adapter built) bracketed into the back. The AC prongs stick out the back of the unit and fold down. I noticed it wasn't charging so started looking at it... instead of folding back the prongs had pushed in and the wires inside must have snapped off. Toyed with the idea of cutting it open and fixing it... but it was 10 watts, which meant it took forever to charge. So, ordered a 2 amp walwart off Amazon for a few bucks and installed it, the tricky part was finding one the same physical dimensions. I still had to cut away some of the inside plastic housing that the old charger fit into (the old one had a curved back, the new one is square). Less secure inside, but seemed okay (might go back and add a couple of drops of superglue).

All charged up and I can already feel the calendar aging kicking in.

I was worried about replacing the old walwart with a newer more powerful version (30 watts) as the charging wires inside are quite thin and might need to be replaced. My meter showed it was cranking out all 30 watts and none of the wires were getting hot after a few hours so I called it good and bolted it up.

Supervstech said:

You don't use them all the time? I have ALL my phone and small electronics running off mine.

Click to expand...

No, I use it when I need portable power (e.g., want to run a 12V airpump, light handtools). Thought I'd use for some 12V benchtop stuff, but haven't gotten around to it yet.

I usually charge my phones and such off the USB walwarts. Used it a lot after making it for powering tools for outdoor projects, not so much recently. Been thinking about getting a light-duty ATV winch and using it to haul the kayak out the water, but it just seems decadent.

...I'm still tinkering with my 1800Wh beast though... that much LFP is HEAVY!...

Click to expand...

You know, without photos it never happened!

Substrate said:

...that's where it stays. 6 years later you are 6 years older.

Click to expand...

Except it always seems like it was just a few weeks ago. Surprising the PJS will turn 3 this fall.

Oh man - that was the classic breakage point for those units - you aren't the only one.

In the "Peak Jump Start Forums" (just kidding), the usual "mod" was to initially attach a small extension cord to the back, and from then on put the daily wear and tear of plugging with the extension jumper end and never remove it from the jump starter box.

Wow - I totally forgot about that.

Being a total battery nerd, I took a different way out since I didn't like the generic charge profile of the wall-wart circuitry:

** SAFETY WARNING **
WITH THE AC POWER DISCONNECTED - I took a different approach by turning the switch to make the clamps active. Not touching of course. And then reverse-charge through the now active cigarette lighter port with 3rd party chargers.

Then another method I used higher quality chargers, like Battery-Minder, Tecmate/Optimate what have you to charge via the clamps. So I didn't need to open the case or make any circuitry.

But anyway, charging via the clamps *SAFELY* while active, (or reverse via the cigarette lighter port) with higher quality chargers really extended the life of the unit. And no more mucking about with the internal wall-wart.

But again, if you leave the clamps active and forget about it, yeah, that's bad from a safety standpoint. Not recommended if one is inattentive about the state of the clamp-active switch.

Substrate said:

Oh man - that was the classic breakage point for those units - you aren't the only one.

In the "Peak Jump Start Forums" (just kidding), the usual "mod" was to initially attach a small extension cord to the back, and from then on put the daily wear and tear of plugging with the extension jumper end and never remove it from the jump starter box.

Wow - I totally forgot about that.

Being a total battery nerd, I took a different way out since I didn't like the generic charge profile of the wall-wart circuitry:

** SAFETY WARNING **
WITH THE AC POWER DISCONNECTED - I took a different approach by turning the switch to make the clamps active. Not touching of course. And then reverse-charge through the now active cigarette lighter port with 3rd party chargers.

Then another method I used higher quality chargers, like Battery-Minder, Tecmate/Optimate what have you to charge via the clamps. So I didn't need to open the case or make any circuitry.

But anyway, charging via the clamps *SAFELY* while active, (or reverse via the cigarette lighter port) with higher quality chargers really extended the life of the unit. And no more mucking about with the internal wall-wart.

But again, if you leave the clamps active and forget about it, yeah, that's bad from a safety standpoint. Not recommended if one is inattentive about the state of the clamp-active switch.

Click to expand...

Heck...
I just clamp my jump boxes to my scc in my suburban...