Charging algorithm and in-car electronics

[y_p_w]

I got curious and monitored the voltage on a new battery maintainer I bought for my parents since they barely drive one of their cars. The battery wasn't completely dead, but it was down to about 9.6V which obviously wouldn't start it. I know a lot of the newer battery charging circuits use more complicated charging where the voltage is constantly changing to improve charging efficiency and do stuff like desulfating. Older ones use fairly steady charging voltages and basically only monitor for . I figure it's not a big deal with something like a new battery being charged before being installed, or AA batteries being charged after they've been removed from any device that uses them. When I checked the voltage it was varying a lot from around 3V to 12.6V, which I understand is desulfation.

However, what would this do to the electronics, which are still operating off of the system voltage? I know most electronics have regulators and most don't really need the nominal 12V. The lights, radio, and chimes were still working with 9.6V. However, it's forcing the battery voltage to quickly oscillate in what's supposed to be a reasonably steady DC environment.

 

[Quattro Pete]

Originally Posted By: y_p_w
When I checked the voltage it was varying a lot from around 3V to 12.6V, which I understand is desulfation.

3V seems way low, unless it was a completely dead battery that you were attempting to revive. Normally, I would expect the charger to push somewhere around 13-15V into a healthy battery.

Here is a charging diagram for one of my chargers (Solar PL2320):

Quote:
However, what would this do to the electronics, which are still operating off of the system voltage?

Like you said, the electronics should normally have some leeway in terms of voltage that they can tolerate, but in general, I would avoid using any of the electronics while the battery is charging. Granted, you don't have control over some of these electronic gizmos.

 

[Quattro Pete]

Here is one for BatteryMinder 2012:

 

[y_p_w]

This seems more like what I saw:

 

[Quattro Pete]

Oh, OK, so it wasn't constant 3V. It was pulsing. Got it.

Which battery maintainer is it?

 

[barryh]

9.6 volts is technically a very flat battery so it would need desulphation mode.

 

[y_p_w]

Originally Posted By: barryh
9.6 volts is technically a very flat battery so it would need desulphation mode.


Well - it's a little more complicated than me just going out and slapping this maintainer on to try and charge the battery. I had actually tried hooking it up to a 12A charger first, but needed to bring it home. I'd bought them an old Harbor Freight maintainer, but I'm not all that confident about using it. After I'd had it charged for an hour it wasn't anywhere near being fully charged. I used my main charger to simply get a readout of what voltage the maintainer was putting on. The voltage was definitely oscillating.

 

[y_p_w]

Originally Posted By: Quattro Pete
Oh, OK, so it wasn't constant 3V. It was pulsing. Got it.

Which battery maintainer is it?

I think I'll probably get a bit of flak for this, but here goes......

It's a Schumacher SC1. It's only been available for a few months and the only place I can find it sold (even online) is Walmart for less than $10 before tax. It's a 0.75 amp nominal wall-wart with a captive cable and clamps. It has a single LED with four settings - powered (flashing green), charging (green), charged (off), and reversed (red). I kind of messed up with the clamps and can verify that reversed detection does work.

I'd actually charged it for about an hour with a Schumacher SC-1200A-CA at 12A so it would at least start. Then I went out in this car to buy the maintainer. I was also using my charger later to detect the voltage being put out by the SC1, since it will measure voltage when it's initially connected. When it's in charge mode it flashes between 12 and an estimated percentage of battery charge.

My dad needed something that even he could figure out and not burn the garage down in case of error. He is downright lousy with electronics. A maintainer with a 6/12V switch would confuse him. A maintainer with quick-release cable connects would phase him out, even if I put it in an he never changes it. A charger (like mine) where buttons have to be pressed until the correct lights flash would be out of the question, and I guess it's not supposed to be used for long-term maintain even though it does automatically go into float mode.

 

[Quattro Pete]

Seems like it would be OK for purely maintaining an already fully charged battery. I don't think that I'd use it for anything else.

 

[y_p_w]

Originally Posted By: Quattro Pete
Seems like it would be OK for purely maintaining an already fully charged battery. I don't think that I'd use it for anything else.

It's obviously not designed for anything else. I think their higher-current maintainers are marketed as suitable for actually charging lawn equipment or motorcycles batteries. I lent my 1.5A one to a coworker who just couldn't get a jumped battery to start more than once. She couldn't drive it more than a few miles and the battery couldn't start after a few hours sitting. I think her husband hooked it up overnight, and while it probably didn't fully charge the battery, it was no longer at such a low charge that overnight was enough that it would fail to start.

Still - a Schumacher rep says the SC1 has a desulfation mode, and that's not terribly useful unless it's going through a good deal of the charging and not just topping off.

http://www.batterychargers.com/sc1/

 

[wrcsixeight]

A 12 volt lead acid battery is considered 100% discharged when resting at 10.5 volts. There is so little usable energy stored below this resting voltage level.

A continued load on a sub 10.5v battery will quickly tank the voltage further and damage the battery.