Voltage reading

Soundguy · Aug 30, 2005

( it is impractical to charge a battery by paralleling it with a power supply without current limit )

I'd refine that to say that for long term charging it is impracticle.

To simply 'boost' a weakoned battery.. a constant current charger is fine.

( Any practical voltage regulator that charges a battery must have some sort of tracking circuit to maintain its voltage somewhere above the varying battery voltage )

I imagine that a simple float style circuit would be fine.. as charge votlage raaches max.. current drops off.. etc.

( and use some sort of current limiting device. )

I'm not a big fan of ham handed technicians or engineers tossing in power resistors to make up for circuit design flaws or out of tolerance operating parameters.. etc.

I've got an electric scooter charger on my bench right now repairing it. Unit has obviously been thru factor re-work several times with the addition of much point to point wireing, as well as an infamous power resistor in line with the output. Very brittle design that IMHO was just wainting to 'let the smoke out' when it left the factory...

While I'm not super hapy about ineficient designs either.. semiconductor current limiting is a bit more tolerable than power disipation.. I.E. series pass regulator.. etc.

I wasn't overly thrilled with the yanmar charge system either.

As I remember we were thinking the dynamo was also a permanent field setup.. leaving the user to regulate the charge voltage to varry charge current. I think collectively we came up with about a dozen ways that worked better than the yanmar method.. however some were component intensive.. and more expensive than the yanmar replacement regulator or the 'will-fit' kholer regulator. Some were nearly as impracticle.. however did work.. etc.

I can't remember if a triac or switching design was mentioned or not?? In any case.. it was a low "I" system..

Soundguy

Mickey_Fx · Aug 30, 2005

No need to take diplomatic approach Reb . Give it some thought about the need to have a current limiting device.

In a constant voltage charge scheme one can think of this as being no different than siphoning a fluid between two containers.

In place of electrons flowing let's make it H2O. Two containers, one full, the other less than full. Containers are hooked together via a tube/pipe and lets add a valve so we can either have the tube passage either open or closed. The container are the same height but of different capacities. You want to think of the full container as a infinite supply. These container represent a supply/charge source and the empty container can be thought as the battery.

Open the valve and observe what happens. At first the flow is relatively high and restricted by the resistance of the connecting tube and the pressure difference. As the "empty" container starts to fill, the flow will slow and eventually stop when the water levels are equal in height (eq pressure/voltage). This is exactly what take place in a constant potential charge scheme that LA batteries prefer.

As long as delta V is not zero there will be current flow from the higher potential. A nom 12V LA battery can rise to ~13.8V and be held there without damage to it. As mentioned in an earlier post, the engineering application literature I've read said charge voltage should run between 2.2 and 2.4 volts a cell with the lower voltages required the longer the battery is to be charged. For cyclic charging like one would find in this kind of application a charge voltage between 2.35 and 2.38 is a good compromise between quickly charging and not extended periods of sustained over charging. And as someone else mentioned, temperature compensation could/should be included but in this kind of application, temp comp if included, it's not very sophisticated.

If one were to see a supply voltage above 14.4 it would be exceeding the recommended charge voltage I've seen recommended in engineering literature by several battery manufacturers.

Oh, in the manual I have it say the alt produces ~14V A.C. The manual also mentions brushes and a commutator. For only having two wires, brushes and a commutator seem strange. On some Yanmar models, if the charge voltage is not regulated, then I could see the need for a current limit. Maybe on the F series tractors the voltage is better controlled than on some models so there is no need for a current limiting devise, the schematic shows none.

reb · Aug 31, 2005

Mickey_Fx:

( At first the flow is relatively high and restricted by the resistance of the connecting tube and the pressure difference )

We are probably thinking the same thing and saying something different. The restriction of the flow is the current limiter I have been talking about.

reb · Aug 31, 2005

Designing an efficient and cheap voltage regulator for lead acid battteries capable of fairly high current is undoubtedly a real challenge. Relying on power resistors or even simple semiconductor current limiting circuits leads to lots of wasted power and heat. The schematic diagram that evofxdwg posted a while back used a neat scheme with SCRs in the bridge which could be turned off as the battery charged to its proper level. The schematic was not complete, so I find it difficult to understand exactly how it worked, but it appeared to apply high current pulses to the battery and then shut down when the battery voltage reached a voltage determined by a zener diode and a couple of diode drops.

pruntyc · Aug 31, 2005

As I remember it, and that I do remember it, tells you I am pretty old. But the old Indian motorcycle, didn't even have a limiter, as such. We would slide the brushes a little, it had a way of doing it, and that was how you cut the current down or up, to the battery. And it seemed to work, and the batteries lasted as good on them as on other things at that time. So I'm not sure it is really that important, that we hold it at an exact setting. My YM1700 has had the same cheap battery in it for over 3 years, and works great, even after setting for a long time.

reb · Aug 31, 2005

I'm with you when it comes to using a machine: the simpler the better. However, you can imagine the lawsuits today if the rider hurt himself while adjusting the brushes or caused some problem with the cycle due to his misadjusting them. Besides, it is more fun to design the Rube Goldberg solutions to the problem.

Soundguy · Sep 1, 2005

( Relying on power resistors or even simple semiconductor current limiting circuits leads to lots of wasted power and heat )

That's one reason i don't 'favor' those circuit setups.

( while back used a neat scheme with SCRs )

I'm guessing a triac circuit would also be fine. This again goes back to 'easy and cheap'. The easy and cheap circuits that the average person can build are grossly ineficient.. the elegant circuits require a bit more electronics knowledge.. not to mention a handfull of parts that cost 3x as much as a cheap float charger from walmart.

( apply high current pulses to the battery and then shut down when the battery voltage reached a voltage determined by a zener diode and a couple of diode drops. )

I'm guessing you could use a mosfet and cook up a variable PWM and do the same.. and just make it taper off based on charge voltage.. again.. not cheap or easy ( to the beginner ).. etc.

Soundguy

Soundguy · Sep 1, 2005

( However, you can imagine the lawsuits today if the rider hurt himself while adjusting the brushes )

If he's talking about a '1' wire 3rd brush type of generator.. they were common back in the 30's and 40's

It was a pseudo B-circuit design generator... one side of the field was grounded.. the other side of the field was attached to the '3rd' brush.. the brush had a small range of movement usually manually controlled by actually turning the brush holder through a arc range of motion.. depending onthelocation of the 3rd brush.. it provided more or less power for the field.. which then produced more or less charge on the armature.

Early ford N series tractor used setups like this. The idea was to start the tractor.. then adjust the generator for about a 2-3 amp charge.. if you turned lamps on.. you had to re-adjust.. or if you left it too high.. the battery might boil.

The brush holder generally had a small dial or knob right on the casing of the genny for adjustment on many of the units i have seen... some were slotted for a screwdriver.. etc.

Soundguy

Mickey_Fx · Sep 1, 2005

( Mickey_Fx:

( At first the flow is relatively high and restricted by the resistance of the connecting tube and the pressure difference )

We are probably thinking the same thing and saying something different. The restriction of the flow is the current limiter I have been talking about. )

Maybe so. With a regulated charge voltage set to the correct point, current will be self regulating as the delta V decreases as battery voltage rises.

I personally don't have a lot of knowledge about all the charge schemes that Yanmar has used but the "current limiter" that has been spoke about is not present on the schematic I have. Also the stated 14V AC mentioned in the manual appears to be less than some have mentioned on their model.

All the difficulty in regulating the charge comes from IMO the lack of a electromagnetic field in the alt like we find in all autos. If the alt design was the same then regulation would be simple.