Car flooded Lead acid Batteries - Question for Lead Acid expert (in search of lost wisdom)

[flippy]

its very hard to test actual cranking. the industry uses 100A for 30 seconds for this reason as this can be done with a basic tool. due to the longer load you can compensate for the higher peaks in most situations.

specialized SLA shops will usually have nicer toys that will go deep into the nitty gritty of a battery/cell bur for the poor peasant folk like us you can do it with a basic tool, its just that most people dont test long enough or dont know how to read it.

 

[Matador]

If your really want so see the amperage spike, can be done with an ameter shunt and an oscilloscope. The shunt will read voltage drop a across it' s terminals that will be proportionnal to the current (for example : 50mV for 100A). Then the oscilloscope can graph the current surge in function of time (mV per millisec), assumuing you know the mV to A convertion factor of your shunt. But for me I'm satified with my ballpark method. Yeah not quite accurate, but it gives me a good ballpark. I'd be in a different mindset if the battery dropped dow to6V during crancking. But 11V +/- 1V error (prrsumed due to low time refreshing rate of voltmeter) seem good enough to give me a sense that this is still not at the end of its life.

Matador

 

[john61ct]

Higher-end Fluke ammeters claim to get to a pretty decent resolution.

But as above, it's not so relevant to sizing cables, ACRs etc in practice since for such short bursts.

Of course when the captain's cranking for longer than a few seconds due to engine issues, then risk increases of overheating at high-resistance points, so oversizing never hurts.

BSS ML ACR specs set a great example, never heard of one failing from cranking overcurrent

https://www.bluesea.com/products/7622/ML-ACR_Automatic_Charging_Relay_with_Manual_Control_-_12V_DC_500A

 

[flippy]

But 11V +/- 1V error (prrsumed due to low time refreshing rate of voltmeter) seem good enough to give me a sense that this is still not at the end of its life.

that approach does not work in many modern cars. they simply refuse to work under 10V. older cars (specifically the ECU) usually craps out around 9V. so that 1V certainly is a problem. you need 0.1V accuracy when doing these tests and run them long enough to actually matter.

Higher-end Fluke ammeters claim to get to a pretty decent resoltion.

inrush currents can usually ony be measured on AC mode. virtrually no ammeter has a DC inrush mode.

Higher
But as above, it's not so relevant to sizing cables, ACRs etc in practice since for such short bursts.
Of course when the captain's cranking for longer than a few seconds due to engine issues, then risk increases of overheating at high-resistance points, so oversizing never hurts.
BSS ML ACR specs set a great example, never heard of one failing from cranking overcurrent
https://www.bluesea.com/products/7622/ML-ACR_Automatic_Charging_Relay_with_Manual_Control_-_12V_DC_500A

cable size is very important, especially on low voltage systems like cars. the only game here is voltage drop prevention. this is why starters have a direct wire that is usually 2ft at the most between the battery and the starter relay.

 

[Punx0r]

I have never seen an ECU fail to operate at any voltage where the starter is capable of turning the engine, no matter how slowly. So unless manufacturers have dropped their design standards considerably in the last few years, you can assume most ECUs can cope with wide voltage transients.

Disconnect the coil, crank for 10 seconds and ensure voltage stays above 10V = servicable battery. Unless you have an unreliable engine, battery drain issue, cold weather or some other condition that will demand more from your battery.

And yes, inrush current is much greater. ~100A will not get an engine turning IME.

Any vehicle rarely used, disconnect the battery.

 

[flippy]

I have never seen an ECU fail to operate at any voltage where the starter is capable of turning the engine, no matter how slowly. So unless manufacturers have dropped their design standards considerably in the last few years, you can assume most ECUs can cope with wide voltage transients.

read Bosch service manuals before making such claims. most (older) ecu's give up their ignition system around 9V. a voltage you can easely get with a dodgy battery.
modern ECU's are even worse thanks to the power requirement of direct injection systems. latest generation used in mercedes already stops the starter when the battery is under 10.5v for more then .2 seconds. aint modern electrics grand....

 

[john61ct]

virtrually no ammeter has a DC inrush mode

Sorry dude that's a complete crock!

Not talking min/max but peak hold, something like 400 samples in 100ms? can capture a peak lasting only 1 ms

peak vs inrush not quite the same, but in this case either are useful

Flukes can and do measure DC inrush just fine, 375 / 376 and remote display 381 for example.

https://youtu.be/2xIsmRkpQLA
http://support.fluke.com/find-sales/Download/Asset/1629920_6115_ENG_B_W.PDF

Keysight U1213A also

Hioki also
https://youtu.be/P0Ho_va9Lk0
https://youtu.be/jXERSwlQdoM
http://hiokiusa.com/wp-content/uploads/pdf/28674-CM4370_en.pdf

Been around long enough, even some Uni-T / Mastech / Extech at the high end prolly do too by now.

Apparently the manuals aren’t trustworthy on that topic.

Higher
But as above, it's not so relevant to sizing cables, ACRs etc in practice since for such short bursts.
Of course when the captain's cranking for longer than a few seconds due to engine issues, then risk increases of overheating at high-resistance points, so oversizing never hurts.
BSS ML ACR specs set a great example, never heard of one failing from cranking overcurrent
https://www.bluesea.com/products/7622/ML-ACR_Automatic_Charging_Relay_with_Manual_Control_-_12V_DC_500A

cable size is very important

Obviously, not sure where you got the idea I said otherwise.

The heat safety issue being completely different from V drop, many device types can tolerate lots of drop so NBD for bursty loads, but

for sensitive devices and continuous usage need to go to big cables, sometimes AWG 00 or even fatter, say cranking big diesels from a bank 20' away.

The BSS app Circuit Wizard is good for sizing, breaks out all the variables for you.

 

[flippy]

i think we can both agree that almost nobody -not even mechanics- are spending 500+ on a ammeter unless you are doing specialized stuff. that is well outside the range of what any consumer would spend and also not even many regular elechickens would buy.
prehaps my whole point about testing methods for simple consumers or mechanics was not clear enough.
and most ammeters ( up to prosumer grade) simply dont have the update rate to catch a DC pulse properly. trust me i tried. and even the expensive stuff like the flukes.

i got a 376 and 381 and BOTH are REALLY shitty in catching DC pulses. right now i just grab my scope with a current clamp and catch the waveform.

personally i dont like using apps to rate cables. i stick to reputable brands and the rating the manufacturer gives for their cable. there is WAY too many variables to trust a app, especially when dealing with 100+ amps. 1 mistake can have dire results.

 

[john61ct]

I only use one type of boat wire, same characteristics across a dozen manufacturers, they don't have different ratings, just some are more honest / better quality than others.

And there are a dozen use case factors that affect the calculation, sheathed or not, bundled or not, ambient temps, how long that highest rate will hold.

Blue Sea's engineers know what they're doing, and in this litigious world believe me their interpretations of the UL and ABYC specs is plenty conservative.

 

[Matador]

i think we can both agree that almost nobody -not even mechanics- are spending 500+ on a ammeter unless you are doing specialized stuff. that is well outside the range of what any consumer would spend and also not even many regular elechickens would buy.

and most ammeters ( up to prosumer grade) simply dont have the update rate to catch a DC pulse properly. trust me i tried. and even the expensive stuff like the flukes.

i got a 376 and 381 and BOTH are REALLY shitty in catching DC pulses. right now i just grab my scope with a current clamp and catch the waveform.

Why bother with an ammeter measure millivolts across ammeter shunt in time on an oscilloscope. But anyways, this thread was about if you guys thought my bayyery was shot or not. I said 11.01V +/-1.0V to use a very conservative margin of error because i'm using a cheap DMM voltmeter. But really I think a get the same voltage drop from a brand new battery. Now if it went much lower voltage (eg 6V) during cranking, then i would know it was shot... But car started right away after 2-3 turns...

Good enough for my purpose.

Matador

 

[Punx0r]

read Bosch service manuals before making such claims. most (older) ecu's give up their ignition system around 9V. a voltage you can easely get with a dodgy battery.
modern ECU's are even worse thanks to the power requirement of direct injection systems. latest generation used in mercedes already stops the starter when the battery is under 10.5v for more then .2 seconds. aint modern electrics grand....

I gave a caveat for very new stuff because I haven't messed with it. And yes, that's pretty lazy engineering. Older stuff, though, if it turns, it will attempt to fire. Spark will be diminished at the lower voltage, but it is functional. That includes early stuff like analogue electronic and mechanical injection systems. Hell, even carb and points if you think about it. There may be an oddball exception but I've never heard an anecdote of "it turned but voltage was too low to attempt to fire".

 

[flippy]

There may be an oddball exception but I've never heard an anecdote of "it turned but voltage was too low to attempt to fire".

cars with stop-start features run into this problem. they have high rpm starters that will run at lower voltages. mercedes had a infamous run with their first gen stop-start system and would fail to start when the battery went bad. it would still crank but fail to inject fuel. it was fixed with a capacitor mod box, but still....

just replace crappy batteries and you will not have any issues.

 

[dogman dan]

Back to Matators problem. Sure, wait till next spring to buy a new battery. But here is the deal, don't shut it off someplace you can't get a charger plugged in, or get a jump from somebody.

So what I mean is back into that parking spot, or somehow park where you can get at the front of the car. Its going to leave you someplace, if you park, and it cools off a few hours.

FWIW, it was summer that killed the battery, always.. But its winter when you notice the capacity got that low and it strands you. I'm not sure if carrying one of those lithium jump starter packs would help you when its seriously cold, but it should be able to start your car if its still fairly warmed up.