What Causes GPU Charging Current To Rise?

[Fly Boomer]

1 minute ago, A64Pilot said:

Most multimeters can measure small amounts of current.

If you disconnect a battery cable when yiu touch it back to the battery there should be no or at most a tiny spark, if there is a significant spark then of course you have s drain.

With the cable disconnected the multimeter an be placed inline to the cable and battery and will measure any current flow, everyone I’ve owned is fuse protected if the draw exceeds the current capacity of the multimeter, which isn’t large

The meter I use all the time is just a little pocket-sized cheapie.  If I smoke the thing, it won't be the end of the world.  Somewhere in the hangar, I have a clamp-type ammeter if I can find it on short notice.

[A64Pilot]

3 minutes ago, Fly Boomer said:

I don't think it was on long enough to reach any thermal limit, and the internal fan cycled on and off which tells me the machine is protecting itself.  What happened is the voltage was set at 28.2.  Usually the current inflow starts high and comes down rapidly.  The current did go high (higher than I had seen it before), and the current did come down, but eventually the current started going back up and, when the power supply hit the maximum current it could supply at 28.2 volts (a little over 20 amps), it switched from constant voltage to constant current and started reducing the voltage.

The current should not have come down, it should have stayed at 20 amps, unless as you speculate the power supply reduced voltage in order to reduce current, only reason I can see it doing that was to protect itself

So why did the current come down, why didn’t it remain at 20 amps?

Voltage is of course for lack of a better word the pressure that will push current into a battery, you can hook up a 1000 amp power supply to a battery and if the voltage is correct the battery can’t be harmed because voltage will hit set point immediately and the battery will only accept what it can

[A64Pilot]

1 minute ago, Fly Boomer said:

The meter I use all the time is just a little pocket-sized cheapie.  If I smoke the thing, it won't be the end of the world.  Somewhere in the hangar, I have a clamp-type ammeter if I can find it on short notice.

Start with the clamp of course but they can’t measure tiny current, that’s where the multimeter comes in.

Clamp meters actually measure magnetic field of course and infer current from that, an amp or two is a tiny magnetic field, but of course even a 1 amp load will kill a 50 AH battery dead in two days

[Fly Boomer]

3 minutes ago, A64Pilot said:

So why did the current come down, why didn’t it remain at 20 amps?

I'm no EE, but what I suspect is that the device I have is only capable of a certain number of watts output.  You can set the voltage, and let the current float.  Or you can set the current, and let the voltage float.  In this case, because the current "requirement" couldn't be met at the voltage I specified, the power supply began reducing voltage to stay under some maximum watt output.  The thing plugs into a 120-volt circuit that will probably provide only 15 or 20 amps, so that sets a ceiling on what the power supply can provide.  Maybe I should just use a conventional battery charger, which maintains 12 or 24 volts, and, if the battery is way down, it will peg the amps until the state of charge is such that the amps will start to come down.  Unlike my GPU/power supply, the battery charger will maintain a constant (non-adjustable) voltage no matter what.  I didn't realize that my power supply would exhibit this behavior, because I had never had a load on it that topped out the max amp draw.  It's just a relatively cheap Chinese box, so you get what you pay for.

[A64Pilot]

The only downside I see to using a power supply as a charger is it won’t drop to float and as expensive as aircraft batteries are I want to float them. I actually have seven batteries on float chargers in my hangar as we speak  Three cars, one motorhome, two airplanes and the pump on my fuel tank. Motorcycle and lawn mower no float chargers.

A charger is of course just a power supply, one that you cant adjust voltage on, unless it’s a “good” charger that’s programmable.

Watts are of course for lack of a better term the “real” measurement of power, because amps depends on voltage, 10 amps at 12V is 120 watts, and 1 amp at 120 volts is 120 watts. Of course that’s dumbing it down, but I’m no EE either.

 

[A64Pilot]

26 minutes ago, Fly Boomer said:

I'm no EE, but what I suspect is that the device I have is only capable of a certain number of watts output.  You can set the voltage, and let the current float.  Or you can set the current, and let the voltage float.  In this case, because the current "requirement" couldn't be met at the voltage I specified, the power supply began reducing voltage to stay under some maximum watt output.  

It should have hit and stayed at the max current, but here is the thing, many, heck probably most things now from welders to battery chargers etc have a duty cycle, real common for example for a 200 amp welder to have s 20% duty cycle, which means of course you can only use it for 12 min per hour at that current, cheap items often just burn up, better ones can and will turn current down to prevent that, and battery chargers as you say regulate current with voltage.

[Fly Boomer]

2 hours ago, A64Pilot said:

The only downside I see to using a power supply as a charger is it won’t drop to float and as expensive as aircraft batteries are I want to float them.

I have a BatteryMINDer for the float, but until I get them back up to something near 100%, I need something a little bigger.

[A64Pilot]

On 9/6/2024 at 3:11 PM, Fly Boomer said:

I have a BatteryMINDer for the float, but until I get them back up to something near 100%, I need something a little bigger.

Agreed,

            I know it’s a PIA but if charging them to 100% and ensuring that you have no dark current I think the next step could be pulling them out, charging and testing them individually.

Give Concorde a call, they are knowledgeable you aren’t given some idiot who knows nothing and has the same troubleshooting guide you do and they are friendly and helpful, besides it doesn’t cost anything and you have nothing to lose.

[Fly Boomer]

3 minutes ago, A64Pilot said:

Agreed,

            I know it’s a PIA but if charging them to 100% and ensuring that you have no dark current I think the next step could be pulling them out, charging and testing them individually.

Give Concorde a call, they are knowledgeable you aren’t given some idiot who knows nothing and has the same troubleshooting guide you do and they are friendly and helpful, besides it doesn’t cost anything and you have nothing to lose.

I think I will.  When I was trying to salvage the previous batteries, they put me in touch with an engineer.  That's well beyond what passes for service these days.

[A64Pilot]

Oh and 20 amps at 24V is of course 480 watts, which is actually a LOT of power, that’s plenty of charger, remember if voltage is correct then you can’t have too big a charger, your power supply ought to do just fine.

Absorption voltage of a Concorde 24V battery ought to be 28.6V, so that’s the voltage you should set your power supply to for charging. 26.6 V for float

[Fly Boomer]

1 minute ago, A64Pilot said:

Oh and 20 amps at 24V is of course 480 watts, which is actually a LOT of power, that’s plenty of charger, remember if voltage is correct then you can’t have too big a charger, your power supply ought to do just fine.

Absorption voltage of a Concorde 24V battery ought to be 28.6V, so that’s the voltage you should set your power supply to for charging. 26.6 V for float

I didn't remember that number, but I will go back and re-read the CMM and the User Guide.

[A64Pilot]

I have been told several times by a few at Concorde that essentially their Lifeline batteries are the same as the Concorde named batteries, just the Lifeline are meant for non-aviation use.

The Lifeline battery manual, I guess maybe somewhat because it doesn’t have to be FAA approved is a heck of a lot more comprehensive manual, in fact it’s the best battery manual by far that I have ever read including Rolls Surrette etc.

‘Give it a read.

https://lifelinebatteries.com/wp-content/uploads/2015/12/6-0101F-Lifeline-Technical-Manual-Final-5-06-19.pdf

[Fly Boomer]

21 minutes ago, A64Pilot said:

I have been told several times by a few at Concorde that essentially their Lifeline batteries are the same as the Concorde named batteries, just the Lifeline are meant for non-aviation use.

The Lifeline battery manual, I guess maybe somewhat because it doesn’t have to be FAA approved is a heck of a lot more comprehensive manual, in fact it’s the best battery manual by far that I have ever read including Rolls Surrette etc.

‘Give it a read.

https://lifelinebatteries.com/wp-content/uploads/2015/12/6-0101F-Lifeline-Technical-Manual-Final-5-06-19.pdf

Thanks.  I have a copy, and have gleaned some gems from the "not approved" manual.

[A64Pilot]

As someone already pointed out in this thread, a 24V battery is just a box with twice as many cells than a 12V one has, so therefore voltages for a 24V battery or bank are of course exactly twice what they are for a 12V battery, and a 6V half of the 12V.

[Fly Boomer]

1 minute ago, A64Pilot said:

As someone already pointed out in this thread, a 24V battery is just a box with twice as many cells than a 12V one has, so therefore voltages for a 24V battery or bank are of course exactly twice what they are for a 12V battery, and a 6V half of the 12V.

I just went back to my Lifeline manual, and found the useful section on "boost charging" batteries that don't go into service immediately (mine didn't).  I don't recall seeing that info in the regular Concorde manuals.

[MikeOH]

@Fly Boomer

If you are going to use a constant voltage power supply make sure to compensate for temperature if above 25C (77F).  I think you need to reduce the charge voltage by about 0.04V per degree C (best check me on that number!)

[Fly Boomer]

1 hour ago, MikeOH said:

@Fly Boomer

If you are going to use a constant voltage power supply make sure to compensate for temperature if above 25C (77F).  I think you need to reduce the charge voltage by about 0.04V per degree C (best check me on that number!)

Right.  I dropped the voltage a bit based on the Concorde recommendations for voltage regulator settings.  That said, as far as I know, our voltage regulators don't adjust themselves as temperatures change.

[A64Pilot]

On 9/7/2024 at 8:33 PM, Fly Boomer said:

Right.  I dropped the voltage a bit based on the Concorde recommendations for voltage regulator settings.  That said, as far as I know, our voltage regulators don't adjust themselves as temperatures change.

They don’t, our VR’s are really primitive things, no three stage charging, temp compensation or anything else, just dumb 14 or 28V plus or minus all the time.

But then we don’t really cycle our batteries in normal use, starting pulls huge current, but it’s such a short time it discharges a healthy battery very little. The short period of time the Ammeter is high shows that, the battery is recharged usually before takeoff.

In truth Auto batteries and ours are constantly overcharged, but obviously they tolerate it rather well.

Old Army helicopters that had Ni-Cad batteries we adjusted the VR twice yearly, in spring and fall, it wasn’t much difference I think maybe a half a volt, that was their attempt at temperature compensation.

Wet cell aircraft batteries use a higher concentration of acid than automobiles do. I assume that a Concorde VRSLAB battery is the same no matter the label, that’s what I’ve been told anyway.

My Engineering contact at Concorde was Skip Koss, who I believe pretty much designed their AGM batteries, but I’m nearly certain he has Retired as that was quite a long time ago and he wasn’t young even then.

Concorde is a family owned and run business, or was anyway. If your talking to someone with the last name Godber, that’s the family name.

Used to be everyone’s Email addresses were first name@lifeline.com, not Concorde.com. I never asked why

Edited September 11, 2024 by A64Pilot