Surface charge/charger

[Duffyjr]

I understand you need to wait for the surface charge to be eliminated to accurately test a battery with a volt meter but what I was wondering is if it's a good idea to wait to put a charger on it. I have a CTEK 4.3 so lets use that charger as an example if it matters. No where in the manual does it mention surface charge. I just put a new battery in my Buick a couple weeks ago and have been playing around with one of those volt meters you plug into a cigarette lighter socket. In the mornings it's down to 12.45ish so I'm guessing they sold me an old battery or I just need to put in on my CTEK. Pretty sure the alternator is ok. This morning it started charging at 14.70 and by the time I got to work ten minutes later it was at 13.90.

 

[barryh]

I've only ever thought of surface charge as impacting on an open circuit voltage tests to determine the state of charge of a battery. I guess you are asking does it impact on an automatic battery charger in terms of the voltage it senses. If it does it has to be a universal thing that charger manufacturers have always taken in to account. If the vehicle has been in use I tend to wait before charging anyway to allow the battery to cool as temperature also impacts on voltage and charging current.

 

[Donald]

Originally Posted By: Duffyjr

I understand you need to wait for the surface charge to be eliminated to accurately test a battery with a volt meter but what I was wondering is if it's a good idea to wait to put a charger on it. I have a CTEK 4.3 so lets use that charger as an example if it matters. No where in the manual does it mention surface charge. I just put a new battery in my Buick a couple weeks ago and have been playing around with one of those volt meters you plug into a cigarette lighter socket. In the mornings it's down to 12.45ish so I'm guessing they sold me an old battery or I just need to put in on my CTEK. Pretty sure the alternator is ok. This morning it started charging at 14.70 and by the time I got to work ten minutes later it was at 13.90.

I would first check accuracy of your voltmeter before you take any action. Know anyone with a Fluke?

 

[379KITTY]

I discovered a similiar issue awhile back, which also prompted me to get a DVM that plugs into lighter. I had noticed that at times my phone would charge as expected, other times very little. My 2005 I learned controls alternator output via the PCM/ECM (pick your term), as opposed to internally regulated alternators as in recent past. After some in-depth research, I learned the PCM will let alt output/batt volts drop to as low as 12.2 at times before ramping up output. All in the quest for fuel economy. Certain things supposedly prevent this (high blower and high beams, rear defogger), but confirmed with DVM and driving. Another technology not unlike stop/start, although probably not as effective.

 

[CharlieBauer]

I wondered this too. You could always remove the surface charge to be sure. But I would think that this is taken care of by the smart charger or does not affect getting it fully charged through the absorption stage. After all, as soon as the battery is charged by the smart charger, won't it begin reading a surface charge anyway? Or is the current too low to create a surface charge?

 

[Duffyjr]

Originally Posted By: Donald

Originally Posted By: Duffyjr

I understand you need to wait for the surface charge to be eliminated to accurately test a battery with a volt meter but what I was wondering is if it's a good idea to wait to put a charger on it. I have a CTEK 4.3 so lets use that charger as an example if it matters. No where in the manual does it mention surface charge. I just put a new battery in my Buick a couple weeks ago and have been playing around with one of those volt meters you plug into a cigarette lighter socket. In the mornings it's down to 12.45ish so I'm guessing they sold me an old battery or I just need to put in on my CTEK. Pretty sure the alternator is ok. This morning it started charging at 14.70 and by the time I got to work ten minutes later it was at 13.90.

I would first check accuracy of your voltmeter before you take any action. Know anyone with a Fluke?

No Fluke but I have tested it against my Craftsman meter and they were identical.

 

[gathermewool]

Pretty sure the smart chargers compare voltage and voltage CHANGE (dV/dT) for the given charge current, so the surface charge won't matter at all. I get rid of the surface charge for measurement, if I need to (I rarely do), by turning on the headlights for a minute while the engine is off. For hooking up my smart charger, I'll sometimes do so and turn it on soon after stopping the engine after parking. The percentage full indicator may read erroneously high at first, but it tends to charger longer if I haven't charged it in a while (thank you fuel efficiency-oriented charging logic!) and less if it's been driven for on long trips or been charged recently.

 

[JHZR2]

This does happen sometimes. Not always. On my MB diesels with no real electronics, often when I turn the engine off, if I connect a charger, it will report 100% and be fooled. It's simple enough to burn off a surface charge.