Got a new Toy! PowerMax Boondocker adjustable 60A

[RDMueller]

Add me to the list of those who are putting aside the automatic "smart chargers" and going with something manual! I've messed with the on board Wiffco, a Battery Tender, various wall warts and the crazy Schumacher, learning as I go. Now I've finally found something that I think is going to work great (Thank you BFL)!

Fully adjustable up to 15.5V, but unloaded it gets pretty close to 16V. So it should be good for regular charging and equalizing. Maybe a little low for desulfating, but hopefully if I take good care of my batteries, I won't need to desulfate. Plus, for under $30 I can add the Drok boost voltage converter to the mix (Thank you Mex), and adjust the amperage as needed. At 60A, I can do a quick charge off the gen when dry camping, then when I get home, I can charge at C/20.

Now the only thing I haven't decided yet is whether or not to add an ammeter. It would definitely be useful, but I'm thinking I can get basically the same info by plugging the Boondocker into the Kill a watt.

[RDMueller]

Ok, ran a test today charging the group 24 Interstate. After the equalization charge I did yesterday, it was at 12.6V and 1.260-1.265 in each cell. Maybe not 100%, but better than this battery has seen since I started all this.

So, I applied a known load to pull about 25Ah out of the battery. Let it rest for about 30 minutes and got about 12.3V. Set the Boondocker to 14.8V unloaded and hooked it up. Took readings every 15 minutes. Voltage at the terminals, wattage from the Kill a watt.

0:00 13.55V 800W
0:15 13.50V 208W
0:30 13.58V 135W
0:45 13.64V 95W
1:00 13.67V 67W
1:15 13.69V 50W
1:30 13.70V 35W
1:45 13.71V 31W
2:00 13.72V 25W

At this point, had to be in abs but it looked like I'd never get to 14.8 at this rate. So I bumped it up to 14.8V (loaded) and the watts went up to 33. Over the next 15 minutes the voltage held steady at 14.8 and the watts dropped to 20. Over the next hour those reading held steady, 14.8V and 20W.

Obviously need an ammeter, that's the only way I'll really know what is going on. Also the DROK will give me far more control.

Overall, I'm going to say I'm enjoying being involved and learning about charging. I really am starting to understand how this is an art to some degree. Sure, much easier just hooking it up to an automatic and waiting for the soothing green light. But easier doesn't = better.

[RDMueller]

Mex, thanks for the cruz pro link. That is a good article, well written and easy to understand!

[BFL13]

With my four batts a 90-50 is about 180AH to play with to run that down before the recharge at 50.

Microwave etc takes say 20 minutes of that at av 100 amps = 33AH while most of the draw is under 15 amps. 20 hr rate is about 22 amps.

So 33AH out of 180 is high draw while most of the rest is less than the 20 hr rate. So how far off can the Trimetric get on the discharge side? Not a problem--don't need no steenkin Peukert correction.

[MEXICOWANDERER]

Shamelessly ripped-off excerpt from a CRUZ PRO column


http://www.cruzpro.com/ahmonitr.html




Most people are aware that their batteries should be sized so that they are discharged about 50% of their capacity before recharging. If you regularly discharge your batteries much more than 50% or much less than 50% you will not be obtaining optimal value for your dollars. Given we accept this to be true - how do you know when the batteries are 50% discharged and when they are fully charged?

Voltmeters and battery acid specific gravity (S.G.) testers are not good indicators of battery charge unless the battery has "rested" for a while. This is especially true for deep cycle batteries with their thick plates. Battery voltage and specific gravity will continue to change long after you have stopped charging and removed all loads from your battery. Battery voltage indicators or LED bar graphs are notoreously error prone and specific gravity testers can be messy and a nuisance. Sealed gel batteries and AGM (Absorbed Glass Mat) don't allow access to the electrolyte to test them with specific gravity testers. So how do we quickly, easily and accurately determine the state of charge of our batteries?

The answer lies in the use of a special battery gauge called an amp-hour monitor. This is a smart electronic instrument that uses a computer to track and calculate all the energy both entering and leaving the battery bank. It can be likened to a fuel gauge for your fuel tank - only much more accurate. The CruzPro VAH30 and VAH35 Amp-hour monitors use a current shunt to measure the current entering the battery and automatically apply an efficiency factor to compensate for losses due to less than perfect charge storage. For most wet batteries the efficiencies range from 70 to 85% (you get back 70-85% of the energy you put in). For AGM batteries the charge efficiency factor is closer to 90% and both CruzPro models enable you to specify the charge efficiency (which you learn by trial and error). That takes care of battery charging, but what about when we discharge a battery?

When a battery is discharged, things get a lot more complicated. The discharge effieciency is not a straight percentage like charge efficiency but a rather complicated equation that the amp-hour monitor has to calculate continuously. Mr. Peukert figured out why a 100 A-H battery discharged at a five amp rate will last 20 hours (5*20=100), but the same battery discharged at 20 amps will not last 5 hours but might only last 3 hours and 20 minutes. Through careful measurement he was able to determine an equation that accurately relates the size of the battery, the discharge rate and the amount of energy remaining. Peukerts law mathematically states the relationship between effective current and actual current. The difference can be amazing as the graph in Figure 1 shows. Amp-hour monitors that do not use Peukert's law can be out by a whopping 300-400% percent!

[RDMueller]

Ah, ok there is a loss in the battery itself during charging as well, however the Trimetric compensates for this. Starting to make more sense. 🙂

[Larryect]

You guys are discussing issues above my knowledge level. But, I would think there would be some losses trying to put amps back into the battery as evidenced by battery heating and gassing.

[BFL13]

Nope 🙂 AH out is what you see, but AH in has the heat loss, so you must put more in that you get out.

How much to allow for heat is a moving target. From 50-70 SOC not much heat, then 70-90 there's more as "gassing voltage" is reached, then there is a lot from 90-100.

Trimetric picks a compromise amount which you can adjust if it doesn't match your own results.

[RDMueller]

BFL13 wrote:
Confusion between Peukert Effect and charging efficiency? The Trimetric instruction manual has some good notes on all that. Worth a read.

Also the Magnum manual has something about the specs being at 25F it goes off the specs other than that, and he was having all sorts of over-temperature problems causing it to do its charging pull-back trick.

I don't trust all this kill-a-watt method instead of just reading the amps without really knowing what the conversion factor is. Needs a calibration cross-check. But to do the cross-check you need an ammeter, so just use that in the first place 🙂

Yes, I think I have started to jumble it all up in my mind. So basically Peukert Effect, not significant enough to worry about. Charging efficiency, really significant losses there, however if you use a DC ammeter between the charger and battery the losses are occurring before you get to the ammeter. Then, Ah out should be pretty close to Ah back in. Think I've got it now!

[BFL13]

Confusion between Peukert Effect and charging efficiency? The Trimetric instruction manual has some good notes on all that. Worth a read.

Also the Magnum manual has something about the specs being at 25F it goes off the specs other than that, and he was having all sorts of over-temperature problems causing it to do its charging pull-back trick.

I don't trust all this kill-a-watt method instead of just reading the amps without really knowing what the conversion factor is. Needs a calibration cross-check. But to do the cross-check you need an ammeter, so just use that in the first place 🙂

[RDMueller]

BFL13 wrote:
The lower capacity at higher draw is for when you draw right down to 10.5v. When you only run a high draw for a short time, the battery bounces back, so you get some capacity back for lower draws. Also the low draw times compensate for the high draw times. Works out close enough. Trimetric manual has some notes on why they don't bother with Peukert.

I ran some tests on this a few years ago and it came out like the Trimetric guy says. One of the other monitors does use Peukert but that is over-refined for the job IMO (and Trimetric's)

Ok, that makes sense. However, as full_mosey posted (and I plan to try today with my setup) it took him 1.87kWh of charging to replace 1.0kWh drawn from the bank, and that's with a PFC charger running at .98 or higher. So that .87kWh went somewhere. I'm guessing heat generated by the inverter/converter going each direction. So all the losses happen as you are going from DC to AC and then AC to DC. If you put a monitor in line between the inverter/converter and the battery, the Ah out should be really close to the Ah back in? In other words, no significant losses occurring in the battery itself?

[BFL13]

The lower capacity at higher draw is for when you draw right down to 10.5v. When you only run a high draw for a short time, the battery bounces back, so you get some capacity back for lower draws. Also the low draw times compensate for the high draw times. Works out close enough. Trimetric manual has some notes on why they don't bother with Peukert.

I ran some tests on this a few years ago and it came out like the Trimetric guy says. One of the other monitors does use Peukert but that is over-refined for the job IMO (and Trimetric's)

[RDMueller]

Very interesting, and gives me an idea for another test I can run. I'll do the same thing, run a ceramic heater through my 1200W inverter for a specific time so I know exactly how many kWh have been removed. Then charge with the Boondocker plugged into the Kill a Watt and see how many kWh it takes to fully recharge.

Also, this brings up another question I've had. So deep cycle batteries are rated in Ah at the 20 hour rate. Draw it out quicker and the capacity is actually less, slower and it's more.

Now AFAIK people use monitors like the Triametric to measure Ah out and Ah put back in. Seems to me that if you always discharged your battery at exactly the 20 hour rate, It would work fine. But since this is not the case, I don't see how this works.

The best analogy I can come up with is this. Say you had a gas tank with no fuel quantity gauge. If you carefully measured the fuel as it's removed, you'd always know how much you had remaining. Take 10 gallons out, then measure 10 gallons back in and you'd know you are right back where you started.

But... If the size of the tank was constantly changing based on the rate at which you were drawing fuel out, you'd never know how much you had remaining using this method. :h. That's why I have a hard time understanding how something like the Trimetric provides useful info.

[BFL13]

That Magnum is nice unit with a well-written manual!

On the watts vs amps thing, what about that 84% "charger efficiency" in the spec? Do you apply that?

I see it says it has "active" PF correction, which came up in another thread, where somebody said a converter would have to have that type of PF correction.

I don't know how this works, but since it has PSW, why does it need a True RMS meter to read the voltage? I thought that was to do with MSW.

[full_mosey]

MrWizard wrote:
output !!
50amps 15v = 750w
50amps 14.4v = 720w

850 is an over estimation


INPUT ?

The user manual specs on page 39 claim that 7AAC input gives 50A of DC charging, right?

7A*120V=840W input, right?

The 50A DC output could be at various output Volts as governed by the bank's acceptance rate and according to the bank's temperature, right?

I do use the Magnum temp-comp cable.

HTH;
John

[MrWizard]

output !!
50amps 15v = 750w
50amps 14.4v = 720w

850 is an over estimation


INPUT ?