Difference In Battery Charging From Different Sources

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Difference In Battery Charging From Different Sources

August 01, 2016, 12:05:58 pm

I have always wondered why the charge presented to batteries, as measured by our battery monitor, differs depending on the power source. If the solar array says it is getting 14amps, the battery monitor agrees - less what ever gadget is turned on.
When the genset is turned on, the monitor will initially say 40 amps are going to the battery, but the number goes down a few amps each second until it stabilizes around 15 amps. Same kind of deal when charging from the alternator. It's a 45amp charger, so if the genset can produce 40, why isn't that passed to the batteries? In lay terms, why the difference?

It is always faster to charge from the solar panels than either the genset or alternator.

Re: Difference In Battery Charging From Different Sources

Reply #1 – August 01, 2016, 06:17:25 pm

Quote from: Don Malpas - August 01, 2016, 12:05:58 pm

I have always wondered why the charge presented to batteries, as measured by our battery monitor, ame kind of deal when charging from the alternator. It's a 45amp charger, so if the genset can produce 40, why isn't that passed to the batteries? In lay terms, why the difference?
It is always faster to charge from the solar panels than either the genset or alternator.

When the coach battery needs charging, the engine's alternator should produce more than any other source, unless you have a very large converter.
If your LD's alternator doesn't, they may be a problem with the wiring or isolator.
I have seen the alternator put 70+-amps into the battery for a short period, more than our upsized 70-amp converter can provide.

The generator only runs the converter and does not directly charge the battery.
The charge rates are dependent on how the charging source is controlled. The alternator is regulated by the engine's computer, responding primarily to the engine and starting battery's needs.
The converter has its own programing as well as the solar controller. Each device will charge at it's own rate, depending on how it was designed.
Solar controllers will hold high charge voltages longer than the engine's or converter's controllers.
I assume that's because the solar controller is trying to extract the greatest amount of solar energy and the sun in only up part of the day.
The converter and/ or engine can run continuously and have a greater chance to overcharge the battery, so a more conservative charging strategy is used.

Larry

Re: Difference In Battery Charging From Different Sources

Reply #2 – August 01, 2016, 07:39:41 pm

I read your words, but I can not make them apply to what I am see. If the batteries are down say 40amps and the monitor initially shows 40 amps going to the battery when the generator or engine is started, but it rapidly falls off to 15amps, what could cause that? The monitor reading when charging from solar never drops off until the batteries are full. It's over my pay grade.

Re: Difference In Battery Charging From Different Sources

Reply #3 – August 01, 2016, 08:55:08 pm

Batteries will accept only so much charge before their voltage rises to the same point as the maximum voltage which the charging source supplies. At that point, you will see the charge current decrease as the battery continues to charge up.

Not sure what charge controller you have, but modern multi-stage controllers will charge at full solar current output until the battery voltage rises to a set value, typically about 14.3V, and the output is clamped there. The current to the battery will start to taper off, until it reaches usually about 1 Amp or less, then the controller will switch to a lower maintenance voltage, and the charge current will drop even more. Alternators will put out about 14.3V from the get-go, at a high charge current, until you turn the engine off, so charge current will start off high, then slowly taper down, but never drop down the way a multi-stage converter or solar controller may seem to suddenly 'turn off' when they switch to maintenance mode.

Steve

Re: Difference In Battery Charging From Different Sources

Reply #4 – August 02, 2016, 12:02:41 pm

I understand what you are saying Steve, but it does not address what I see happening.

Situation - Battery down 40 amps, certainly a level where it can initially accept max charge.

Turn on genset or alternator, which initially sends about 40 amps to the battery. After a few minutes, the charge going to the battery drops to about 15amps. It will continue to slowly drop over the next hour to about 12amps, LONG before the battery is close to being fully charged.

or

Turn on the solar, and suppose there are enough photons to send 15amps to the battery and the sun is stopped and there are no clouds. It will continue sending 15amps until the battery is nearly full.

It's been over 50 years since I learned anything about volts, amps, ohms, so perhaps amps is the wrong metric to judge the charge level being presented to the battery?? It is a reliable metric for storage capacity and the charge remaining, but perhaps not for judging charging? But, that does not seem right. A typical battery charger for automotive use has three amp settings, one for a slow trickle charge, say 2amps, one for fast charge, say 10amps and one for boost, maybe 50amps.

Re: Difference In Battery Charging From Different Sources

Reply #5 – August 02, 2016, 12:35:10 pm

Don

What converter does your LD have? Have you upgraded or is it the stock converter?
The stock converter acts the way you are describing, no matter if it is powered by the generator or shore power.
It is a poor converter with minimal output.

Changing to to a high power converter will provide larger output, held for a longer period, before dropping off.
This will allow significantly shorter generator run times, when the battery is low.

Larry

Re: Difference In Battery Charging From Different Sources

Reply #6 – August 02, 2016, 05:14:06 pm

I put in a PD 45 years ago.

Re: Difference In Battery Charging From Different Sources

Reply #7 – August 02, 2016, 08:16:14 pm

Don, the key is to monitor both voltage and current. The battery will determine how much charge current it can accept, depending on the voltage of the charging source. If at the same state of battery charge the solar controller is charging at 15 amps and the converter at only 12 amps, you'll see that the solar is putting a higher voltage on the batteries. Matter of fact, it sounds like the solar controller may be malfunctioning. Does it maintain about 14.3v or does it go above that after awhile? Note too that the alternator voltage will drop as the chassis battery charges up, which is typically quickly.

Steve

Re: Difference In Battery Charging From Different Sources

Reply #8 – August 03, 2016, 10:03:10 am

...the alternator voltage will drop as the chassis battery charges up, which is typically quickly.

That accounts for the quick drop by the alternator and also why it takes so long to charge that way. That's not a method we use, but I have observed it and this explains it. Obvious now that you point it out.

I have no reason to think the solar is not working right. In fact, it is the fastest way to charge the batteries. Day after day, we get back to full charge with just a few hours of sun that produce 9amps. It's been that way for nine years.

I am not complaining or suggesting any system is not working as designed. Just wondering why the charge rate falls off fast from the genset or alternator. The latter is now explained. The former remains a mystery to me.

Re: Difference In Battery Charging From Different Sources

Reply #9 – August 03, 2016, 11:31:39 am

Don, I would still double-check the voltage output of your solar charge controller to make certain it never exceeds about 14.3V, and drops down to 13.2-13.6V once the charge current has dropped to 1A or less. Note that the Heliotrope models do NOT do this, and are notorious for overcharging and causing premature failure of batteries, usually when the rig is unattended for long periods with little battery drain.

Overvoltage from charging sources not only can damage batteries, but test the upper voltage limits of electronic equipment and light bulbs in the rig. Note that any equalization modes should be disabled for AGM batteries, and used only in carefully controlled conditions with flooded-cell models, with everything else turned off.

Steve

Re: Difference In Battery Charging From Different Sources

Reply #10 – August 03, 2016, 04:32:55 pm

Steve, I am thinking you think I have a problem with solar system.
I will answer your concerns, then I am going to write to my USN trained electrical guru and see if he can answer my query.

We have a HPV-22B. The dip switches were set by Mike Sylvester 8 years ago when he installed the system. I would never touch them. I fully trust that Mike did the right way.

Right now we are 98.5% charged. Just a few more amps to shove in.
The solar controller is sending 12a at 14.5v.
The monitor shows 14.1 going to the battery.

Re: Difference In Battery Charging From Different Sources

Reply #11 – August 04, 2016, 12:02:57 am

Quote from: Don Malpas - August 03, 2016, 04:32:55 pm

Right now we are 98.5% charged. Just a few more amps to shove in.
The solar controller is sending 12a at 14.5v.
The monitor shows 14.1 going to the battery.

Don, I'm a bit confused - I believe you are saying the battery monitor is reading 14.1V and 98.5% charged. What does it say the charge current is? If all 12A from the solar controller are going to the battery, and you have 225 A-hr of battery, then the 98.5% charge is wrong. If some lights and other appliances are using some of that 12A from the solar, and only 3A or less is actually showing on the battery monitor, then that would make sense. If this is not the case, then you either have a calibration error of the battery monitor, and the 98.5% is not accurate, or a battery problem.

In general, the current reading of the solar charge controller is only useful for determining proper function of the solar power system - it would seem your HPV-22B is working as Heliotrope designed it - but it is not a 3-stage system, so it will never go automatically to a maintenance mode. There is a front panel switch to do that manually. There is a history with these Heliotrope controllers overcharging batteries and causing premature failure, both with the Trojans, and particularly with the AGMs Lazy Daze installed in later years.

Steve

Re: Difference In Battery Charging From Different Sources

Reply #12 – August 05, 2016, 09:40:04 am

Quote from: Steve - August 04, 2016, 12:02:57 am

There is a history with these Heliotrope controllers overcharging batteries and causing premature failure, both with the Trojans, and particularly with the AGMs Lazy Daze installed in later years.

Steve

At the time I originally installed AGMs, about 6 years or so ago, the mis-match of their particular charging requirements and the HPV22B charge controller's ability to do so apparently wasn't widely understood. The HPV22B charge controller that I had in the LD at that time allowed overcharging to damage the batteries to the point of one actually developing a 2" split. The current (in my rig) combination of AGMS, Blue Sky 3000i, and a PD multi-stage converter has played well together for more than a year so far.

As ever, YMMV.

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