Battery Charging

[Monterey385]

I know Main Sail has extensive postings on this topic so perhaps any answer already exists and someone can point me to it.

How can I check the actual amperage output from my alternator and the true amperage input at my battery bank when the alternator is charging?

I have a 120 amp alternator, a house bank of two 4D batteries (I think 205AH each), and a starter battery. My house bank appears to be dropping faster than the voltmeter suggests it should but I can’t be certain that the alternator is topping off the batteries when we are on moorings (I have a great charger when at the dock).

Even sometimes when we return to dock my 30 amp charger has to run for a considerable number of hours in spite of a 1-1.5 hr motoring transit.

 

[capta]

I have installed a Blue Sea M2 1834 CD multimeter on this boat, and it gives the true voltage and amperage going into or out of the house bank. If you wanted to know the charging amperage of the alternator, then you could put an ammeter in that line as well.

 

[jssailem]

Here is one answer...
https://www.fluke.com/en-us/product/electrical-testing/clamp-meters/fluke-325
A DC amp meter.

 

[Monterey385]

Okay ... duh moment time ... is it as simple as putting my multimeter on my battery posts and setting it to amps? I do volts all the time but haven’t measured current.

 

[dlochner]

For long term monitoring an ammeter is the answer, for the short term a clamp on meter like @jssailem suggested will work.

I installed a Victron Battery Monitor. It does a lot, I mostly use to simply measure amps in and amps out.

As for the batteries not charging there are a number of factors that come in to play, including age of the batteries, how is the alternator regulated, internal or external, drain on the electric system while motoring, and probably more.

One assumption that is often made is that the alternator is putting out full output all the time, this isn't the case. Depending on the regulator, it may drop off considerably.

Another assumption is that if 20 amp hours comes out of the battery, then only 20 amp hours need to go back to be fully charged. It doesn't work that way. It always takes more energy to recharge. So, if you take out 20 amp hours, you may have to put back 30 amp hours.

Here are some places to get more detailed information. Well worth the read.

https://marinehowto.com/category/electrical/
https://marinehowto.com/automotive-alternators-vs-deep-cycle-batteries/
https://marinehowto.com/installing-a-battery-monitor/
https://marinehowto.com/programming-a-battery-monitor/

 

[capta]

You cannot measure amps from positive to negative across the wires or terminals. It is measured along one wire, hence the clamp meter.
The meter I mentioned above is installed on the negative wire as close to the negative battery terminal as possible with a shunt in the line.

 

[jssailem]

@Monterey385, It is a question :

1. Do you want a continuously monitored system - Install the inline meters as suggested.
2. Are you occasionally testing to verify function or performance - Use the hand held meter.

I like to set up a good system then do routine checks to verify or log performance change. I do not need to check the battery hour by hour. On a plane that was more critical. On my boat it is a little more laid back. It is more of a monthly or so many hours of use format. Unless I see lack of performance then it is full on inspection time. The Handheld system is very useful in such an event.

 

[Monterey385]

Okay, I think I’m getting somewhere ... I have a clamp multimeter (now I know what the clamp is for -) ... I have several red wires on my terminals ... on is reading 4 amps which corresponds to my current draw meter on my panel, another reads -16.1 amps ... I’m assuming the sign indicates current direction ... if I’ve done this accurately, does this mean I’m receiving 16 amps and using 4 amps thereby netting 12 amps? This would correspond to my battery charge experience while motoring.

 

[dziedzicmj]

@Monterey385 - please note that, from what you have just said, your alternator is outputting 16 A, despite its nominal peak output of 120 A.

 

[Monterey385]

@dziedzicmj ... so noted ... I also just did a voltage test with and without load. With the engine running my batteries are reading 13.8 volts with no DC load (all breakers off and zero amp draw on panel). When I fire up every DC system I’m drawing 17 Amps and the voltage drops to 13.6. Thus I think from a voltage drop under load perspective I am okay. Either I have a bum Amperage reading above (16.1) due to user error or my voltage regulator is really constraining output. This might be by design to prevent cooking the batteries but I am intent to understand this system. Thoughts?

 

[JimInPB]

It's possible that your batteries are just not in the bulk phase of their charge cycle & they can only take in 12 amps at this time without the voltage climbing higher than you want it. There is a limit to how many amps a battery will accept. It varies with state of charge.

It sounds like you got the right kind of clamp-on ammeter. The cheap ones only read AC. The better ones can read AC or DC.

& yes, you are correct about the +/- sign telling you which way the current is flowing. If you put the meter on the same wire backwards, it should read the opposite sign with the same number. If the numbers are different, then your zero reference is probably off.

 

[Gunni]

You would really, really benefit with an installed battery monitor and a temperature-sensing programmable external alternator regulator.

 

[Monterey385]

You would really, really benefit with an installed battery monitor and a temperature-sensing programmable external alternator regulator.

I understand and tend to agree ... next weekend I think I’m heading back to the slip to do some projects and I think tracing and testing this system is my next step. I have to find my regulator and get its specs. I think Catalina installed a special higher end regulator but I’m not sure. Don’t laugh but I wish batteries came with an amp hour gauge (I know volts are essentially the gauge but the surface charge always messes me up)

 

[dlochner]

I understand and tend to agree ... next weekend I think I’m heading back to the slip to do some projects and I think tracing and testing this system is my next step. I have to find my regulator and get its specs. I think Catalina installed a special higher end regulator but I’m not sure. Don’t laugh but I wish batteries came with an amp hour gauge (I know volts are essentially the gauge but the surface charge always messes me up)

One of the simplest and most accurate gauges is the Balmar Smart Gauge. It provides accurate SOC readings and voltages level.

The problem with amp counting gauges is that as the battery ages, its capacity goes down and the amp counter has to be reset to the new amp hour capacity.

I have both a Smart Gauge to measure SOC and a Victron Battery Monitor to measure current flow, realtime amps in and out. So far I like it, tells me everything I want to know. Its also handy for finding current leaks. Just when you thought everything was turned off, you wonder why there is still a .5 amp drain....

 

[Monterey385]

The more I've thought about this ... I think I already have two of the three major items addressed for the house bank. (1) I have a digital voltmeter (not sure of brand, but its pretty accurate) installed for each of the house batteries. I also have a ammeter for the outbound draw that also appears to be pretty accurate. I have an ammeter and voltmeter on the battery charger. What I don't think I have the ability to measure is the alternator to the regulator and the regulator to the house bank. My multimeter (if I did it accurately) addressed the regulator to the house bank. This leaves the alternator to the regulator if I understand the circuit correctly.

I'm pretty sure I can measure the alternator output using my multimeter but is there a better way to get the alternator amp output? Too, is there anyway to confirm the regulator is working properly and not reducing the output inappropriately?

 

[jviss]

What I don't think I have the ability to measure is the alternator to the regulator and the regulator to the house bank.

That's not really how it works. The alternator output goes directly to the house bank, not though the regulator. The regulator senses voltage, preferably at the battery, and regulates alternator field current based on this value, and if a "smart" regulator, what charging mode it's in.

 

[Monterey385]

That's not really how it works. The alternator output goes directly to the house bank, not though the regulator. The regulator senses voltage, preferably at the battery, and regulates alternator field current based on this value, and if a "smart" regulator, what charging mode it's in.

I erroneously assumed the regulator would be in-line between the alternator and the house bank.

Perhaps it would be better to reformulate the question to:

What is the best way to distinguish between an alternator not performing to specifications versus a regulator not performing properly?

 

[jviss]

What is the best way to distinguish between an alternator not performing to specifications versus a regulator not performing properly?

That's a good question! It depends on the symptoms, and the system design. What regulator do you have?

 

[dlochner]

@Monterey385 If you're not completely confused by now, you should be.

Underlying all of this discussion is a simple formula, known as Ohm's Law. It covers the relationship between voltage, amperage and resistance all of which are at play when charging batteries. I would attempt to explain Ohm's law here, but I'd botch it up, suffice it to say that almost all electrical theory and practice based on this simple law. My suggestion is to google Ohm's Law and read a few explanations. Once you have a rudimentary understanding, you will find the answers you are getting to make more sense. And the articles by MaineSail I referenced earlier will also make more sense.

Right now, I have the feeling that we are all like the Blind Men and the elephant, trying to describe in detail the piece of the elephant in front of us. The trouble with this approach is that charging systems are just that charging systems and no one piece of it is independent of another.

 

[JimInPB]

If you want to test what your regulator is willing to put out if the regulator allow it to, then run your house bank down to about 60% & check current flow when charging begins.