Would Higher Octane Run the Gen Better? UPDATE

[BFL13]

UPDATE 21 Nov page 5

Ongoing saga with my 1700w (continuous) gen trying to run my 75 amp charger at 75 amps. Briggs and Stratton P2200 gen.

Previously posted that it would not (flashing overload red light), then discovered I still had it choked. Next test was to run it with the batteries full, but with an inverter draw of 127 amps, then turn on the charger, but now with the gen choke in the right place. Amps now -52 so 127 minus 52 = 75 amps from the converter/charger. No flashing overload light on gen. So I reported success.

Just been camping off grid, did a recharge with the gen and the 75 amper. No red light at first. 75 amps to battery bank. Then after a few minutes the red light started flashing but gen kept running.(It can shut off with overload.) Switched to the 55 amp charger and no red light.

We know that running a charger as a power supply is easier than doing an actual battery recharge due to the higher battery resistance. Sometimes it can do its full amps as a power supply, but might not be able to do its full amps on the battery. BUT--I thought that if it did its 75 amps as supply that was the same effort as doing 75 amps on a battery.

Here, 75 amps on battery seems to take more effort from the charger than doing supply, so needs more from the generator? 75 is not the same 75?

Also there is some relationship between the generator engine running and the power output, as seen when it was choked and did less 120v power. I am wondering if the gen would run the 75 amper without the flashing overload light if only the engine ran a little "better" (not sure what I mean by that in what the engine would have to do) More revs?

The manual mentions engine getting bogged down with too much load-I did not hear it running slower.

So finally after all that background--would the engine do "better" if it ran on higher octane gasoline? It has 87 now (regular). And if it did, would that make the difference to output power I need where I am just on the edge for running that 75 amper?

Engine is 6.77 cu-in(111 cc), 4500 revs single-cylinder, revolving field, wants 87 octane minimum below 2500 ft altitude.

I will not have an opportunity to try that for a while, so I am asking here to learn if it is worth trying at all. Thanks.

[pianotuna]

BFL13,

And the run time may possibly be a bit shorter on premium fuel. I still continue to use it as I do not wish to be replacing/cleaning a carburetor.

[BFL13]

Ran more recharging tests with generator maxed. Going to 91 ethanol- free gas from 81 octane with 10% ethanol made absolutely no difference. Gen runs the same both ways and the overload red flashing light did not change to indicate the inverter was any happier with the 91.

So that answers the question I had in the OP.

[BFL13]

Ok we'll check all that out next chance I get. No worries with PowerMax converters--they do constant amps in Bulk no problem. So do several other brands of course.

Meanwhile I got a gallon of 91 Octane-no ethanol- gas at a Co-Op station, where it does say right on the pumps what each octane (87,89,91) pump's ethanol percentage is--no change from that 2015 info posted earlier.

Chevron has a 94 Octane pump, but no info on ethanol on the pump that I noticed. Most brand stations just have the three octanes and a general notice that they may contain up to 10% ethanol.

So must drain gen, put in the 91, and someday do a 50-80 and take notes. Not today though.

[DrewE]

BFL13 wrote:
My problem is the definition of "output voltage"

You have the battery voltage at 12.2v and the charger is set to 14.8v. connect them. Voltage at the charger is now 13.5v and at the battery it is 13.3v with 75 amps on the wires between them.

As this goes on, battery voltage rises with its SOC. So later you see 14.2 at the charger and 14.0 at the battery. You happen to be at the end of Bulk and amps start to taper.

Voltage at the charger a bit later is 14.4 and at the battery it is 14.3 with 45 amps being accepted. (fewer amps so less voltage drop)

Eventually, you are at 14.8 at the charger and at the battery with no amps flowing. all done.

So what do you use for "output voltage" during the Bulk Stage, which is what I care about. ( Once amps taper for the Absorption stage I am home free because VA required from the gen drops off and no more red flashing light)

At the start of bulk, the converter's output voltage is 13.5V in this example. At the end, it's 14.2V. It rises as the battery charges, and the power output (but not the current output) of this hypothetical converter increases gradually over that time. Whether the current actually remains constant or not is, of course, a different question; some converters are not capable of supplying max current at the max voltage (nor do their specifications necessarily claim that).

[BFL13]

MrWizard wrote:

I need to do a standard 50-80 recharge and see if the gen has to supply as much to the converter at 50% as it does at 70% SOC.

got it backwards again

at 50%soc the battery will accept more amps and converter will be using MORE power, VA will be higher than when when SOC is 70% and the battery is accepting less amps

UNLESS the bank is so large that it can still accept (converter max amps) at 70%SOC, in which case VA will be up, watts into converter will be up because voltage to battery has risen

what size is the battery bank ?
at point does amps into bank start to drop ?



i know in my case amps drops off long before converter reaches 'set point' voltage, set point voltage is not reached until batteries are almost fully charged

The point where amps start to taper depends on the charging rate (and type of battery it seems) but as you suggest, a larger battery bank for the same amps means a lower charging rate and thus a higher SOC when amps start to taper. That is what my ugly graph shows so well (IMO!)

In my example above, I meant that the charger keeps 75 amps constant to 75% SOC then amps taper. I have 450AH of AGMs so 75 amps is only a 17% charging rate. That would correspond to a 37 amp charger on a 220 AH bank. So I would expect Bulk to end at about 80% SOC.

I have not checked that for real with my existing bank. I have lots of graphs from when using the Honda 3000 and Flooded batts in the 5er over the years, but can't be sure they count for anything with these AGMs.

Of course Mex has thrown a scuz into everything with his 20% charging rate requirement so I have to split the bank and do part of it at a time to get the charging rate up over 20% I only do that at home, so no gen required for that. My gen is just for when camping and not enough solar and it will be under the 20% rule for the 50-80 or whatever I do. Too bad so sad! Can't be helped. None of this would be happening if the stupid compartment in this class C would have held the Honda 3000. Oh well.

[MrWizard]

I need to do a standard 50-80 recharge and see if the gen has to supply as much to the converter at 50% as it does at 70% SOC.

got it backwards again

at 50%soc the battery will accept more amps and converter will be using MORE power, VA will be higher than when when SOC is 70% and the battery is accepting less amps

UNLESS the bank is so large that it can still accept (converter max amps) at 70%SOC, in which case VA will be up, watts into converter will be up because voltage to battery has risen

what size is the battery bank ?
at point does amps into bank start to drop ?

i know in my case amps drops off long before converter reaches 'set point' voltage, set point voltage is not reached until batteries are almost fully charged

[BFL13]

My problem is the definition of "output voltage"

You have the battery voltage at 12.2v and the charger is set to 14.8v. connect them. Voltage at the charger is now 13.5v and at the battery it is 13.3v with 75 amps on the wires between them.

As this goes on, battery voltage rises with its SOC. So later you see 14.2 at the charger and 14.0 at the battery. You happen to be at the end of Bulk and amps start to taper.

Voltage at the charger a bit later is 14.4 and at the battery it is 14.3 with 45 amps being accepted. (fewer amps so less voltage drop)

Eventually, you are at 14.8 at the charger and at the battery with no amps flowing. all done.

So what do you use for "output voltage" during the Bulk Stage, which is what I care about. ( Once amps taper for the Absorption stage I am home free because VA required from the gen drops off and no more red flashing light)

[DrewE]

BFL13 wrote:

Why should the converter care how many of its output amps are going to heat and how many are going to raise battery SOC? I am thinking the converter needs the same 120v input power.

OTOH, I still have that problem where it pulls less power when doing its 75 amps while "supplying" than when battery charging. I suppose that is because of less resistance when supplying.

It is also when battery voltage is quite low while being pulled down by the inverter running the MW while the charger helps put amps in at the same time.

I need to do a standard 50-80 recharge and see if the gen has to supply as much to the converter at 50% as it does at 70% SOC.

The converter indeed doesn't care (or even know) what portion of its output is going to heat or to battery charging or, for that matter, to powering a fridge and furnace and XBox. If the output voltage and output current from the converter are constant, its input power consumption should be constant as well (assuming the AC input voltage isn't changing, of course).

The amount of power the converter is outputting at 75A does vary if its output voltage changes. It's not unreasonable to model this as the connected equivalent resistance of the load changing, and of course due to ohm's law this implies the voltage also changes to maintain a constant current. Similarly, the power output of an engine operating at a constant speed changes if the torque required of it varies, and its fuel consumption (input power) is likewise affected.

[BFL13]

MEXICOWANDERER wrote:
You are not dealing with a fixed resistor. But a reactive electro chemical response.

Look up

Charge
Efficiency
Factor

Why should the converter care how many of its output amps are going to heat and how many are going to raise battery SOC? I am thinking the converter needs the same 120v input power.

OTOH, I still have that problem where it pulls less power when doing its 75 amps while "supplying" than when battery charging. I suppose that is because of less resistance when supplying.

It is also when battery voltage is quite low while being pulled down by the inverter running the MW while the charger helps put amps in at the same time.

I need to do a standard 50-80 recharge and see if the gen has to supply as much to the converter at 50% as it does at 70% SOC.

[MEXICOWANDERER]

You are not dealing with a fixed resistor. But a reactive electro chemical response.

Look up

Charge
Efficiency
Factor

[BFL13]

Mr Wiz, I am baffled by the amps always falling while SOC rises idea, when amps are constant during the Bulk stage. Charging amps do fall at the beginning of the Absorption stage and continue to taper.

(Ignoring that little funny part just at the transition between Bulk and Absorption where definitons get muddled)

Battery acceptance in amps goes down as SOC rises, but the current limited charger comes in at below the acceptance rate and holds steady until charger amps = acceptance rate (at that voltage and SOC) when amps then taper.

The gen supplies the VA for the charger doing 75 amps at 50% SOC until say 73% SOC. Battery "resistance" keeps rising that whole time.

I have only spot checks to see what VA is over that Bulk stage and not enough to see if VA goes up with SOC.

I was surprised to be told in this thread by one and all that it does. I can see that output watts goes up with rising battery voltage. That would make peak input watts be just at the end of the Bulk Stage. If PF is changing during the Bulk stage too, then I don't know what happens with VA.

EDIT- input watts might not peak there if efficiency is changing too. Gottaluvit.

Yes I am confused. (My usual state 🙂 )

[MrWizard]

My problem is that I have not seen VA rising (not enough measuring perhaps) during the Bulk stage. Constant 75 amps while SOC rises from 50 to say 73%. Battery voltage rises all during that time.

So I would be looking at VA vs battery voltage in the Bulk stage. I did see on the Kill-A-Watt how the VA components change. Lower 120v voltage and higher 120v amps to it over time. I want to see what that was all about too vs rising battery voltage over a longer time.

why would VA rise, VA is max at empty battery max charge
VA = power
power needed drops as battery SOC rises and the battery accepts less amps
there is NO linear correlation between amps dropping and battery voltage rising
power needed is NOT constant, power needed does not rise, it goes down

VA needed will always be less as the battery charges
the PF will change and efficiency will change
efficiency of power use goes DOWN as the battery SOC rises, but total VA/watts used also goes down just not at a linear rate

IF your looking for a magic number on the KAW that will tell you your batteries are at a certain SOC
Not going to happen

battery use is in a constant state of flux, using anything except one or two little LED lights,
PC, tv, device charging, all have switching power supplies, inverter use to power them, MW and coffee pot, 'Mr Perkuet" etc..

charging is a constantly tapering amps vrs rising voltage, vrs battery SOC and ambient temp which affects the chemical reaction of the both the recharge and discharge

[BFL13]

MrWizard wrote:

I am not happy with the idea the converter requires more VA as the battery voltage rises, for instance. I can test for that over a longer recharge time from a lower SOC

Confuse yourself ?

Efficiency changes as the charge SOC progresses, but the converter does not need more VA to deliver 40 amps charge than it does to deliver 75 amps charge
How ever, When I get down to 4 amps charging, pf is like 0.546
But when it's charging above 70 amps PF is like 0.768 I remember seeing 0.796 at one point

Watts in versus battery charging amps always changes as the battery fills up
That's true of all switching supplies, and our converter is a switching supply

I have seen how the VA required drops right off when amps taper at the start of the Absorption Stage. Battery voltage also continues to rise after that towards the voltage set on the converter.

My problem is that I have not seen VA rising (not enough measuring perhaps) during the Bulk stage. Constant 75 amps while SOC rises from 50 to say 73%. Battery voltage rises all during that time.

So I would be looking at VA vs battery voltage in the Bulk stage. I did see on the Kill-A-Watt how the VA components change. Lower 120v voltage and higher 120v amps to it over time. I want to see what that was all about too vs rising battery voltage over a longer time.

If it is true that VA is lower with lower battery voltage and same 75 amps in the Bulk stage, then I should be able to find a max battery voltage that will still give me the 75 amps at just under 1700VA and not have that red light start flashing.

I can stop the battery voltage getting any higher than that by setting the charger's voltage to just over that.

Then to find if that max battery voltage is at a high enough SOC to call it a 50-80 or whatever.

If the VA stays the same 1700 during the Bulk stage with the red light flashing the whole way from 50%, then that won't work.

[MrWizard]

I am not happy with the idea the converter requires more VA as the battery voltage rises, for instance. I can test for that over a longer recharge time from a lower SOC

Confuse yourself ?

Efficiency changes as the charge SOC progresses, but the converter does not need more VA to deliver 40 amps charge than it does to deliver 75 amps charge
How ever, When I get down to 4 amps charging, pf is like 0.546
But when it's charging above 70 amps PF is like 0.768 I remember seeing 0.796 at one point

Watts in versus battery charging amps always changes as the battery fills up
That's true of all switching supplies, and our converter is a switching supply