Generator and LiFePO4 Charger Test (long and technical)

[bdosborn]

I have a Yamaha 1000w generator that's been having carburetor problems and wouldn't run anything without stalling. I finally took it in and had it fixed, so it was time to test my battery charger to see if the generator would run it. I have an Iota DSL-45 charger with the IQ4 LiFePO4 charge controller. 45amps X 13.8V=621 watts so my guess was that the generator would be right at it's capacity by the time you figure in losses and power factor. The Yamaha is rated at 900 watts continuous. I ran the battery down to 55% capacity, about 80 amp-hrs, to make sure the charger would be in bulk mode. I started the generator and plugged in the charger. The generator lugged a bit, then stabilized but the charger rolled back its output to around 30 amps rather than the 45 amps at full output. Then it continued to roll the output down till it was at 17 amps. Here's a graph showing the amps starting to roll off from 30A.


I unplugged from the generator and plugged it into utility power, and the same thing happened. WTF? I unplugged the charge controller and plugged it back in and boom, 46 amps. The charger maintained 46 amps till the battery was charged. You can see where I unplugged-plugged the controller as the current jumps up to 46 amps This is the entire charge cycle:


Interestingly, the voltage jumped up from 13.5 to around 13.8V with the current bump, which is in the recommenced range for LiFePO4 charging. I like how the charger changes mode at about 14V and tapers the current down to nothing until the battery is at 100% charged. Here's a close up of the charger finishing up:


I used a Kill a Watt to measure some AC electrical parameters while the charger was full output:

Drawing 8.8 amps at 120V:


796 watts output the generator with 634 amps going into the battery. That's about 80% efficiency while charging at full output:


Power factor is awful, as low as 0.6 when the charger was at 20 amps, rising to 0.7 when loaded:


The real surprise was the Volt-Amp load; I wouldn't have guessed the generator would carry this since the power factor is so low. A 0.8 power factor is what most commercial generators are rated at:


So here's some conclusions I've drawn from this test.

-I'll keep my 1000w generator, I was considering trading up to a 2000 but I don't need one yet. The generator won't run the A/C so if I do upgrade it will be to run that.

-The generator wouldn't run in eco mode, it needed to be at full RPM to carry 46A.

-The Iota IQ4 Charge controller has a float mode that holds the battery at 13.5V for 15 days without charging. Then it will switch to bulk mode, charge it back up and return to float mode. I think the reason it wouldn't charge at full output was because it was stuck in float mode. Unplugging the controller reset it. I need to do some reading and see if anyone else has noticed this. Other than that, I like the charge profile of the Iota.

-45A is definitely the largest charger I would run on a 1000watt generator. Its also about the largest charger I can use with my battery. 180 amp-hrs X 0.3C= 54A is the maximum recommended charge rate.

-It's really cool that I can replace 90 amp-hrs of capacity by running the generator two hours. I would have needed a full day to charge lead acid batteries back from that level.

-I use Victron Venus software running on a Raspberry Pi to track the battery voltage and current. I'd never know what was going on without it.

-I haven't had to run my generator while camping for a couple of years now, the PV array usually takes care of what we use. I like to have a backup power source since our fridge is electric.

Bruce

[John61CT]

Does the IQ-LIFEPO add-on allow for adjustment of the voltage?

If that is hard-coded to 13.8V for 4S I'm gobsmacked, that would be a world first I think, congrats to Iota engineers.

But adjustable for user-custom setpoints would still be better, since even 13.8V can still overcharge if the current rate (e.g. with solar) is very very low like below 0.1C

Note that the setpoint is only reached at the very end of the charge cycle, at CC to CV transition.

Unlike charging lead banks, there is no reason to go past that point into an "Absorb" stage, and if a charge source does, it should not be held there very long.

During the "Bulk" CC stage, the charge regulator is just blindly "striving" to hit the setpoint, it is the battery CAR, SoC% and current rate that is actually chemically "negotiating" the resulting voltage curve on the way there.

Of course, increasing the current rate also results in that voltage increasing, all that is bog standard inherent in the physics of how charging works independent of devices and bank chemistry.

I like how the charger changes mode at about 14V and tapers the current down to nothing until the battery is at 100% charged

This also has nothing to do with the charger's regulation circuitry, once Absorb / CV is reached - **voltage** capped by the source - the increasing resistance of the chemical processes as SoC is (over-)charging is what slows the rate down.

If you are allowing those "trailing" amps to decline past an endAmps spec, of say 0.05C that is also not good for longevity, doing so is leftover "lead thinking", where fg spec'd endAmps setpoints of even 0.02C are commonplace.

TBH for bank longevity you should not allow a setpoint that high.

Also, for optimal longevity, LFP should not be Floated at all. If for example you're sitting on shore power, the bank should be in storage mode well below 50-60% SoC isolated from the source carrying loads.

Of course much of the above is just technical background context, not that relevant to your intended generator specific topic, just wanted to clarify misconceptions, feel free to (tell me to) take it to a different thread if you consider it a derail.


> 45A is definitely the largest charger I would run on a 1000watt generator.

Some PF-corrected chargers, and other "nominal 1000W" gensets may get up to 50A, but certainly for 55+A a bigger gennie's needed.

A current-adjustable rectifier gives more flexibility, e.g. when other large loads are needed to run concurrently, or (for sources allowing universal power input) when campsites etc have high-amp 240Vac is available.


> Its also about the largest charger I can use with my battery. 180 amp-hrs X 0.3C= 54A is the maximum recommended charge rate.

Actually that will greatly vary by ambient temperature - actually internal cell temps, and depending on how important cell longevity is, as opposed to getting charged quickly. Some even pre-warm cells with silicon heating pads, or hydronic temp management systems circulating heat / cooling transfer fluids.

Can safely go to 0.5C at 30°C or even higher with little to no harm (lost cycles off the back end).

Below 15°C my limit reco is maybe a 0.2C charge rate.

Close to freezing start considering pre-warming, or a super gentle rate below 0.1C

[fishboat]

... I think the reason it wouldn't charge at full output was because it was stuck in float mode. Unplugging the controller reset it. I need to do some reading and see if anyone else has noticed this. Other than that, I like the charge profile of the Iota.

Bruce

BD,

Nice workup. I too have an Iota (DSL45 w/ internal IQ4) maintaining two 6V 230AH wet cell batts. I used the setup last summer over a half dozen trips...very happy with it. I run a Champion 2000w generator, though very seldom ever need it. We have a very low amp draw trailer and use 12V primarily for refrigeration(Truckfridge 50qt) with a few minutes of lighting in the evening. In shady campsites we can run 5-7 days before charging is needed.

With respect to your observation on "..stuck in float mode..". I haven't noticed this when the system is maintaining charge in the driveway between trips. Every 7 days it does kick into an equalization cycle. Anytime a bulk charge is needed it runs right up to 45 amps and then tails off as needed.

[bdosborn]

I know I read a post somewhere that mentioned unplugging the IQ4 module, but I can't find it anywhere. I might get another IQ4 and see if it does the same thing. It's not really a big deal since I always check the battery meter when I'm charging. I'll just need to remember to unplug if if I see it happening.

Bruce

[fishboat]

I know I read a post somewhere that mentioned unplugging the IQ4 module, but I can't find it anywhere. I might get another IQ4 and see if it does the same thing. It's not really a big deal since I always check the battery meter when I'm charging. I'll just need to remember to unplug if if I see it happening.

Bruce

My IQ4 module is internal, so no unplugging for me. I don't necessarily unplug my charger, but it does randomly get powered down (power to trailer unplugged or charger power is switched off inside the trailer)occasionally..it's possible I haven't matched the conditions that lead to your observation.