Passive Car Battery Trickle Charger

That is the primary reason for doing this. I could easily buy some battery management/topper-upper from China otherwise. --

"Andrey Semyonovitch really was rather stupid; he attached himself to the progressive cause and 'our younger generation' from enthusiasm. He was one of the numerous and varied legion of dullards, of half-animate abortions, conceited, half-educated coxcombs who attach themselves to the idea most in fashion, only to vulgarise it and who caricature every cause they serve, however sincerely."

- Fyodor Dostoevsky

John Larkin's design here I come, then. His is also more efficient. I know I don't need to worry about efficiency given these designs are entirely run by the sun, but mine does get awfully warm around midday and that might cause issues in a closed-up car during the summer months temperature stabilisation-wise. --

"Andrey Semyonovitch really was rather stupid; he attached himself to the progressive cause and 'our younger generation' from enthusiasm. He was one of the numerous and varied legion of dullards, of half-animate abortions, conceited, half-educated coxcombs who attach themselves to the idea most in fashion, only to vulgarise it and who caricature every cause they serve, however sincerely."

- Fyodor Dostoevsky

Well, on that note I did seriously consider (for a bit more fun) building something heliotropic but quickly discarded it as totally superfluous to requirements even in the middle of Winter. It would certainly have been FUNmax though!

--

"Andrey Semyonovitch really was rather stupid; he attached himself to the progressive cause and 'our younger generation' from enthusiasm. He was one of the numerous and varied legion of dullards, of half-animate abortions, conceited, half-educated coxcombs who attach themselves to the idea most in fashion, only to vulgarise it and who caricature every cause they serve, however sincerely."

- Fyodor Dostoevsky

Yup. And, in colder weather, the battery "appears smaller" while the engine "appears bigger". Big difference between a 1.5L and 7L block!

[I look at the starters on newer cars and wonder if they used them in little "kiddie cars"! I can recall needing two hands to heft one into place on older american muscle.]

geared vs. direct drive

Gear reduction starters can be smaller. The maximum torque of an electric motor is proportional to its volume, so the way to get more out of one is to run it faster and gear it down.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

yep, some of the RC brushless motors are a kW peak in a few 100gram but that's at 20krpm

e:

rote:

ics design group.

clearly and his proposed solution is a long way from anything sensible.

olve his problem with junk from his spare parts box - and if he did take up a suggestion posted here he'd almost certainly get it wrong and resist any suggestion that he'd done anything wrong.

kind of 'help' you dish out. :-D

You don't like I when I point out that you are being idiotic. Some people a re silly enough to take you seriously, and they might need that kind of hel p. You would prefer that they didn't get it.

--
Bill Sloman, Sydney

e:

y

to

p

s to be not only fool-proof, but also ingenious-idiot-proof, which is even more demanding.

their job less tedious has made me pretty pessimistic.

ead-acid-batteries/

The article starts with a fallacy, "As you know, lead acid battery electrol yte is a mixture of water and sulfuric acid." With that level of understan ding of chemistry, I'm not sure how to believe anything they say. Sulfuric acid and water form a solution where the mixing is so complete they do not separate.

The only way I can think a battery would have a more concentrated solution at the bottom of the battery would be when pure sulfuric acid was formed on the plates and poured off without mixing significantly with the solution. The article talks about this happening when the car is only driven short d istances. That would tend to agitate the solution promoting more thorough mixing. I think this article has a lot of hooey in it. So it's hard tot k now just when stratification would occur. I do think it much more likely w hen under continuing charge while stationary.

--

Rick C. 

--+ Get 1,000 miles of free Supercharging 
--+ Tesla referral code - https://ts.la/richard11209

is above about 80% charged and reduces the output voltage of the alternator (Honda reduces it to ~12.5V). If the battery is below 80% SOC the voltage will be ~13.8-14.5v.

of-charge.

ive gassing.

That doesn't make much sense. I think you mean when the voltage rises they reduce the current. When a battery is low the voltage is low and you aren 't going to raise it much unless you pump a huge current into it. As it ch arges the voltage rises. When it is getting near topped off they limit the voltage and let the current drop off. Once reaching nearly a full charge the voltage can be dropped back to a "float" charge level, but I don't thin k cars do that. It would make the headlights dim and such. I think the al ternator puts out a max current at whatever voltage the battery takes, then cuts back the current at the max voltage.

--

Rick C. 

+-- Get 1,000 miles of free Supercharging 
+-- Tesla referral code - https://ts.la/richard11209

ote:

ery

s to

d

eep

/2

has to be not only fool-proof, but also ingenious-idiot-proof, which is eve n more demanding.

ke their job less tedious has made me pretty pessimistic.

-lead-acid-batteries/

olyte is a mixture of water and sulfuric acid." With that level of understa nding of chemistry, I'm not sure how to believe anything they say. Sulfuric acid and water form a solution where the mixing is so complete they do not separate.

n at the bottom of the battery would be when pure sulfuric acid was formed on the plates and poured off without mixing significantly with the solution . The article talks about this happening when the car is only driven short distances. That would tend to agitate the solution promoting more thorough mixing. I think this article has a lot of hooey in it. So it's hard tot kno w just when stratification would occur. I do think it much more likely when under continuing charge while stationary.

You can pour concentrated sulphuric acid into water slowly enough that it d oesn't mix immediately, and you can get a layer of concentrated sulphuric a cid on the bottom of the container, for a short while, but as the water dif fuses into the concentrated sulphuric acid the interface gets warmer, and e ventually boils, mixing the two layers much more rapidly and throwing fluid in all directions. It is a trap for young players, and you have to warn fi rst year chemistry students about in practical classes

Battery charging happens a lot more slowly, and - as you say - gives quite enough time for diffusion to even out any concentration gradients. You don' t see a layer of concentrated sulphuric acid forming in the bottom of a bot tle of 10% sulphuric acid, not matter how long you leave it.

--
Bill Sloman, Sydney

The interesting numbers are open circuit voltage, optimum power transfer and short circuit current. You can measure two of these easily and take a fair guess at the other once you have some data for very different light levels. I don't think it is worth doing optimum power transfer for something so puny. The additional complexity outweighs any gain.

How are you measuring it? Are you aware that a modern vehicle still has quite a few thirsty systems running for between 2 to 5 minutes after you lock the thing down and walk away. Then it drops into a proper quiescent sleep state which IME is more like 20-40mA older cars typically lower.

Combined with battery losses and a 40Ah battery that equates to something like 1k-2k hours (or 30-60 days) to a flat battery.

I have never seen a decent car with a working battery that wouldn't start immediately after returning from a 3 week holiday.

--
Regards, 
Martin Brown

I've already measured it and posted the results, it's around 5 - 10 mA, depending on battery voltage. The drain on the battery from the van electrics is around the same and there is a diesel heater unit in the back whose controller draws another 10 mA if I don't remember to isolate it after it has cooled down. Altogether, the maximumum drain is less than 50mA and the battery is 140 AH, so it will take over 100 days to discharge.

--
~ Liz Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
www.poppyrecords.co.uk

In theory and up to a point. UPS SLA batteries always seem to die horribly after about the same period in regular use no matter what. Sometimes they swell up to a point where they are very hard to remove and before the UPS self test notices they are seriously defective.

I reckon it will need something to take the edge off full whack 600mA as the cells start to reach gassing voltage. PV panels intended for this purpose typically source about 20+v open circuit which is more than enough to damage a fully charged lead acid cell by pushing more current through it long after it has reached gassing terminal voltage.

I just went and measured mine (nominal 12W panel) on a dull thick cloud day with sea fret and it was 22.6v open circuit and 13mA into a dead short. I expect 13mA is less than the car standby electronics draws.

A few series diodes to reduce the peak voltage under load down to a more battery friendly 14.4v would probably be good enough with the caveat of a bleed resistor so that a tiny amount of charging to cover standing current can occur during the hours of daylight under cloud.

A 15v Zener and a series pass transistor would be OK for 14.4v too (overkill?). It might have to dissipate a few watts at most.

--
Regards, 
Martin Brown

Headlight aren't just dumb bulbs connected straight to the supply bus no more.

The internal resistance of a lead acid battery is so low that headlamps would not be much dimmer with the alternator backed off maximum output. I'd guess filament headlamp provide quite a nice ballast load.

Even when they were it would be a puny alternator that couldn't power headlights and still charge the battery a little. Dynamos in old cars tended to struggle in British long dark winters with push starts needed back in the good old days when batteries often went flat in mid winter.

--
Regards, 
Martin Brown

That question was for George. My mistake for editing it badly. Apols for any confusion. --

"Andrey Semyonovitch really was rather stupid; he attached himself to the progressive cause and 'our younger generation' from enthusiasm. He was one of the numerous and varied legion of dullards, of half-animate abortions, conceited, half-educated coxcombs who attach themselves to the idea most in fashion, only to vulgarise it and who caricature every cause they serve, however sincerely."

- Fyodor Dostoevsky

Yeah I'm aware of that and cautioned some other poster about it further up this thread in fact. I like to measure current for extended periods using my old Avo 8 as DVMs use up current from their battery, even if it's only a small amout. Analogue still rules for certain purposes. Peaking tuned circuits springs to mind here. --

"Andrey Semyonovitch really was rather stupid; he attached himself to the progressive cause and 'our younger generation' from enthusiasm. He was one of the numerous and varied legion of dullards, of half-animate abortions, conceited, half-educated coxcombs who attach themselves to the idea most in fashion, only to vulgarise it and who caricature every cause they serve, however sincerely."

- Fyodor Dostoevsky

On Tuesday, 2 March 2021 at 23:01:03 UTC-8, snipped-for-privacy@gmail.com wrote: ...

ssive gassing.

y reduce the current.

No, they explicitly do reduce the voltage. In the case of the Honda I menti oned it was 12.5V once the battery is estimated to be at a reasonably high SOC. A Chevy manual I read had three different voltages depending upon circ umstances (that one also had a 500 miles at a higher voltage for one time o nly when the battery was new.

much unless you pump a huge current into it.

Yes, that happens.

imit the voltage and let the current drop off

Yes. Many cars do not have battery current sensors but some do - on the one s I have seen it can be seen around the battery ground lead.

float" charge level, but I don't think cars do that.

Modern cars do exactly that.

a max current at whatever voltage the battery >takes, then cuts back the c urrent at the max voltage.

Not for modern ones. They control the voltage more actively. I don't know i f they control the headlight intensity, with LED lamps they could easily.

In particular, the "engine stop-start" also affects how the battery SOC is managed, if the SOC is too low the feature is disabled on the ones I have r ead about.