Bulk charging stage: What determines amps in?

[Spaceman Spiff]

From   http://www.centurybatteries.com.au/...alk/issue-2-battery-talk-battery-charging.pdf

It took a long walk with the pup this morning to figure out what the Century Battery explanation is talking about, re: constant voltage charging.

I have three constant voltage chargers:
   - One is a 1964 Wards 12V, 6A battery charger.  It provides 6 amps at 13.6V whenever it is plugged in; no smarts.
   - Another is a 30A adjustable voltage power supply that I use for equalizing; again no smarts.
   - The third is a number of battery maintainers, they provide 750mA at ~ 13.4V.  They have some rudimentary smarts.

Constant current charging is what we are talking about here (what they are calling Automatic Battery Chargers).  This includes all (at least all I am aware of) charge controllers, RV inverter/chargers, and moderately priced to high priced battery chargers.  They all change modes according to feedback from the battery.  They all have the three basic modes of charging (Bulk, Absorption, Float), the better ones have an equalize function, and some have modes 5 - ∞ that I have no idea how useful they are.

Speculating here. Higher voltage means higher current flow during Bulk, faster charging, also healthier for AGM longevity.

Any danger from overcharging would come later in the cycle, so it would work to push the voltage to the high end early, get to Absorb stage faster, then back off, for a shorter gentler Absorb stage . . .

That makes sense.  When I had my bulk/absorption voltage set too high (by 0.2V)  I had to refill my batteries every two weeks and the outgassing happened during absorption.

HDR:  I have a Morningstar TS-45.

 -- Spiff

 

[John61CT]

IMO the more automatic and feature full marketing stuff gets in the way.

Example: equalization should be done manually.

Reliability, custom setpoints and lots of amps are what I look for.

Sterling ProCharge Ultra and ProMariner Pronautic P at the top.

Progressive Dynamics and Iota for RV style "converters".

And good power supplies like Samlex and Mean Well.

 

[Zil]

John, could you explain what your Sterling or Pronautic do as far as voltage and amperage? I thought I understood lead acid battery charging.

 

[John61CT]

Why limit yourself to lead?

The sell sheets and manuals are online, feel free to ask any specific Qs.

They are very robust and reliable, will likely be moved from van to van over the years.

Come in a large range of amp capacities, IMO should buy biggest you can afford to handle AH expansion or future purchase of high-CAR chemistries.

Besides the canned bank-type profiles, they (uniquely I believe) give the ability to create a custom user-defined profile.

Since banks are consumable, this last feature will properly charge whatever battery chemistry I may switch to in the future, per mfg specs, rather than settling for "close enough".

Including LFP if I want, better than what any LFP vendor sells AFAIK, no problem if Maine Sail changes his longevity recommendation to 3.55Vpc rather than 3.45 (13.8V for 12V nominal).

Or OceanPlanet decides their Firefly Oasis is better off at 14.6 rather than 14.4

Or setting up for my FLA bank's monthly manual equalization protocol at 16.3 rather than 15.8V.

etc

 

[Zil]

So, you don't understand how they charge or you just are tired of me.

 

[John61CT]

Maybe the problem is, I don't understand your question.

I'm happy to help regardless of my feelings, but the information I give you is likely to be more helpful to you, to the degree you can be more specific in your questions.

How lead batteries charge is well outlined above and in many "battery charging 101" pages on the web.

It is not rocket science, and what makes one charger better than others is not some special "way of charging" different from others' ways.

Put out current at maX amps until volts rise to target V, then hold that V as current declines to Y amps, then go to Float.

Most chargers have (less than ideal) preset values for these variables, these two let the user set them to what your batt mfg specs as ideal for your bank.

 

[Weight]

My charger increases it voltage at the battery gradually in order to maintain the full amperage of the charger. As the battery resistance increases the voltage from the charger increases, up to the set point in the charger. The battery has nothing to do with this voltage increase. After the set point is reached, the resistance of the battery reduces the amperes delivered by the charger. That is after the set point is reached. This stage is what we get with the standard auto store charger. Constant voltage, from the first connection to the battery. My charger does an additional adjustment. After a set time at set point voltage and amps reduced to a set value, the charger reduces the voltage to just maintain the battery, sometimes with no amps going to the battery. Auto store chargers keep the voltage at the same value and will wreck the battery unless disconnected. That is the value of having a premium charger such as Sterling or Promariner.

 

[John61CT]

> My charger increases it voltage at the battery gradually in order to maintain the full amperage of the charger. As the battery resistance increases the voltage from the charger increases, up to the set point in the charger. The battery has nothing to do with this voltage increase.

Sorry to not pick, but no this last is incorrect. those first "two stages" are inevitable for any charge source, even plain "fixed-voltage" power supplies will do the same if you measure the process with a DMM at the battery.

Length of time in bulk to get to absorb setpoint is a function of SoC, charge amps available and battery chemistry, and nothing to do with the "intelligence" of the charger.

While plenty of auto store chargers do go to float just fine, it is true most don't offer adjustability to prevent them doing so prematurely.

Biggest problem with them is amps too low and built too cheaply.

With FLA there is little harm from keeping at Absorb too long, as long as offgassed fluid is replaced.

Yes AGMs are damaged, since such replacement is impossible.

 

[road_ahead]

Very informative. I briefly wondered if a new Odyssey OBC-20A portable charger was not up to spec when it was only delivering around 9 amps instead of 20amps during bulk charging. Before connecting it I checked the battery (EastPenn Deka 8A31DTM) voltage with a Klein Tools CL800 and it read 12.79v. I'll check again when I run it down to 50% SoC.

 

[John61CT]

Yes maximum amps accepted is determined by the battery.

At that SoC even a 300A charger at the same voltage would not be delivering any higher current.

 

[Weight]

With a volt meter on the battery, NAPA 10 amp charger is at 14.1 volts from 12 amps to 1 amp output, will stay at 14.1 until some calamity or disconnected. Same voltmeter, ProNautic 40 amp starts at battery voltage, slowly increase voltage, maintaining 40 amp output. Reaches 14.7 volts, then holds that voltage until 2 amps for some minutes then drops voltage to range 12.8 to 13.4 volts.

 

[John61CT]

The actual combined voltage is **always** a point between what the charger is striving for and the lower bank voltage, that is just physics.

If the above is an actual observation account, **and** you used the same large bank identically well-depleted in both cases, the only explanation I can come up with would be a charger that is actually putting out a much higher voltage in order to arrive at the target in the face of the much lower batt voltage.

This would result in a faster charge given equal current amps.

I haven't seen a charger do that in real life, but then I haven't used any automotive starter-type chargers except for that intended purpose.

 

[Zil]

No.