Samlex SEC 1215UL charger

PNjunction

I just received a 15-amp Samlex SEC 1215UL 2/3 stage charger/power supply and am very pleased.

I ran it through a charge cycle on my Optima agm. Set for 14.4v, and at the end of absorb, my Fluke 87V read exactly 14.40 volts. The 3 stage charge algorithm seems to be the classic taper, with current starting to reduce at 13.8v, and voltage rising slowly. The spec for float is 13.5v, and my Fluke measured 13.49v. I really like stuff that actually performs to spec! (update - after a few hours of float, this creeped up to 13.53v. No problem)

I like the large analog meter to show when absorb is occuring, and although not super-precise, it is close enough as a general indicator. The body of this small amperage unit is convection cooled with two large heatsinks on the sides, and during operation neither got hot enough to make you pull your hand away. For the first run, there was the typical electronics smell, but it was the smell I was used to in the past, not some toxic cloud making you puke from cheaper quality stuff. Of course, an all-metal case is a joy, and while it made no real difference, the yellow on black scheme looks nice.

One of the other voltage settings you can choose is 14.0v, which would be designed for GEL. Later, I'll be testing that with my LiFePo4 battery. These voltages are dip-switch settable on the side. WARNING - as stated in the manual, do NOT toggle both of the switches to off.

Included was a bag containing 4 crimp/solder pins for your own cabling. As nutty as this seems, these were high-quality as far as I could tell. No pot-metal junk. I Zen out when I encounter manufacturers taking time to make sure that they aren't cutting corners on even the small stuff.

It will charge up to 3 batteries at a time, (isolated I think) or function as a power-supply. I really didn't need that flexibility, but like most of the Samlex stuff, the docs are very good and they indicate that if you are trying to balance multiple batteries, you should use the 2-stage charger mode first to get everyone up to 13.8v, and then later switch to a 3 stage with a higher bulk voltage. There are a few other details, and it is all in the manual, which you can find on the net.

As measured on a P3-International Kill-A-Watt meter, while running at full current, I was drawing 255w at 3.5A AC. Temperature was 85F.

I have other chargers that perform many more functions, but I do not regret at all the money spent on basic, yet seemingly high-quality gear. The Samlex seems to get the job done, and most importantly abides by their own specifications. Thumbs up here.

It is also well filtered, VERY quiet in the HF 3-30 mhz radio range. You might find some signals if you go hunting for them, but overall, excellent.

PNjunction

Samlex with LiFePo4 observations

How well does the Samlex do on prismatic LiFePo4's like my 20 and 40ah GBS batteries?

Overall, very nice with a few observations.

The Samlex is programmed for lead-acid with a typical sloping algorithm. Unlike a simple CV charger (that just has overcurrent regulation to protect itself and lets the battery set the absorb regulation on its own) the Samlex does a sanity profile that regulates the current as well, forcing any battery not to exceed a programmed curve for lead.

LiFePo4's have a VERY flat charge/discharge curve with an extremely steep knee at both ends. That means that while charging, there is very little to no absorb as compared to lead. When it is done, it is done. From a solar standpoint, you just stay in bulk to the very end more or less. (one of the reasons I like Lifepo4).

At the start of charge, the 1215UL went immediately from 15A down to about 12A, and held steady thinking it was attached to a lead battery that had already reached absorb. During charge, the Samlex (not the lifepo4!) regulated current and forced it to follow a slower charge profile dropping current all along the way until my 14.0v setpoint was reached.

At first, this means a slower time to charge. In practice however, if you have the extra amount of time, it is not bad at all for LiFePo4!

What this means is that you have PLENTY of time to check pack balance and take appropriate action if necessary. I won't go too far into it here, but for guys like me that see no reason to go beyond 14v, no cell goes beyond 3.6v, and are within .05v (50mv) delta among the highest and lowest cells at the end of charge, I'm good to go. I'm using these as a house-bank, and not needing the precision that an EV or RC modeler needs. My low-current, low voltage storage use with Lifepo4 is different from an EV application, or RC modeler that uses a different unstable chemistry. A simple single-cell charger that brought each of my cells to 3.55v initially was sufficient. (It was set for 3.7v, so I just manually pulled it when 3.55v was reached)

In the end, even though the Samlex is programmed for a sloping lead charge profile, with the choice of either 14.0v, or 14.4v you can run it two ways with LiFePo4. 14.4v may be useful if you rely upon external balancing circuits that bleed / divert charge to other cells. By dropping current according to a lead profile, those external boards will have less current to deal with, which can be an additional point-of-failure killing your cells instead of balancing them. This lead profile curve may actually benefit that kind of operation.

The lower 14.0v is useful for guys like me that simplify and abhor the "drop in replacement" mindset (remember gel's early days?) by merely running at a slightly reduced SOC, and know that .05v delta or less is good enough for a top-balance. Likewise, I don't run these things into the deep discharge knee either. When I hit 12.8v rested, or maybe 12.0v under load, THAT is my LVC point. Since I'm reasonably balanced, and have purchased quality cells, this is sufficient without having to go nuts with individual cell monitors. Go there if you wish.

Yeah, the Samlex is not LiFePo4 specific, but it can be shoehorned into duty or used as a "pre-qualification" charger for an initial charge. It is flexible enough to handle both lead and lifepo4 (not at the same time!). If I had to do it again, because of the programmed lead profile (unlike a simple CV charger), and time was of the essence, I'd choose a unit with an amperage closer to .5 - 1C, since that current will drop immediately when the Samlex thinks it is dealing with a lead battery already in the absorb stage.

After the charge is finished, the Samlex goes to 13.5v float. This is not really necessary, and no current is flowing. While it won't harm anything short-term, there is no need for it, so just disconnect from the charger. Leaving a float voltage with no current flowing on lifepo4 long term is subject to debate and will provide you with endless hours of internet forum fun. I take the point that since there is no NEED for it, pull it as soon as you can or when convenient.

One thing for sure - I don't want my solar charge controllers following a pre-programmed lead profile. CV (pwm or mppt) and letting the Lifepo4 call the shots is what I need here since I don't have the solar-insolation time to goof around, nor waste one of the great characteristics of Lifepo4 that I bought it for in the first place.

PNjunction

Re: Samlex SEC 1215UL charger

PNjunction wrote: »

WARNING - as stated in the manual, do NOT toggle both of the switches to off.

CORRECTION - as listed in the manual on Page 11, turning both switches to OFF enables the 13.5v power supply / 2 stage charger.

You do NOT want to set both of these switches to "on".

In addition, operating as a power supply means that you have to have a load attached to the battery at the same time. I tested it without a load, and the current dropped dramatically. In my case as a power supply without a load, I was only achieving about 6A of current. In the normal 3-stage charger mode, I got about 13A, which will eventually slope lower and lower.

I didn't buy this thing for the power-supply function, but some may find it really handy when they don't want to hold their lead batteries with a load in an endless absorb voltage scenario. That's not good for lifepo4 either, but at 13.5v, you will never achieve a full charge anyway.

My sincere apologies for letting this slip.