How Much Alternator Current Does The Engine & House Batteries Receive When Driving?

[imnprsd]

My 2004 Itasca "Horizon" 40AD was an early model type that did NOT come with the B.I.R.D. relay that allow your alternator to charge my house batteries.

So I installed a Battery Isolator (aka Voltage Sensitive Relay, VSR) and it has been working great for the last 5 years! And I highly recommend this one if your house batteries are not wired to receive a charge while you are driving:

Keyline VSR ($99): https://www.amazon.com/dp/B00WTAFR52...ing=UTF8&psc=1

[I]* The KeyLine Automatic 140 Amp Dual Battery Isolator is all you need to charge Two Battery Systems. Voltage Sensitive Relay (VSR) cuts in at 13.3 volts and cuts out at 12.8 volts to ensure your primary battery is always charged and ready to start your vehicle. It's like having two separate power sources for each battery while only having one alternator! ...And all you do is connect the positive Engine Start Battery terminal to the Keyline VSR and then complete the circuit by connecting the other terminal to the positive House Battery terminal./I]

* I have 2-12V-950CA Engine Start Batteries wired in parallel.

* I have 4-6V-GC2-Golf Cart Batteries (430AH) wired in series and parallel.

* And my new Delco alternator puts out 160A

Questions:

* They also make a 180A Delco Alternator, but I don't know if it's a good idea to increase the alternator Amp output? (Stock on my coach is 160A.) Also, the Delco does NOT use the Remote Sense circuitry the stock Leece Nivell 160A alternator used.

* The Keyline VSR is rated at 140A, but this is the maximum amp rating and not the amount of amps going to the batteries. So I am wondering how many amps are going to the batteries when they are low vs. when they are fully charged?

* If I want to reduce the load on the alternator, does it make sense for me to replace my Halogen headlight bulbs (9007) with LED headlight bulbs?

Note: My 9007 bulbs are the type with high and low beams in one light; and my headlight lens has a reflector. ...I also looked into upgrading to LED lights 3 years ago, but I really did NOT like the quality of the wires and I did not want anything melting down. Plus the LED light output was NOT BETTER than the Sylvenia Ultra bulb upgrade at $55. So I stayed with Halogon and it is far superior than the stock 9007 bulb that came with my coach.

* Has LED headlight technology for 9007 bulb replacement improved over the years? ...And have they come up with better ways to dissipate the heat?

* I don't have much room behind my headlight housing to mount an LED light with a big heat sink. So I would need a dongle setup. Any suggestions?

* I think the principle of the alternator to always "give it all she's got" if the load call for it? I.e., if that VSR opens a circuit to my engine and my house batteries, will all the available alternator amps go to the engine & house batteries; and will my alternator will always be putting-out 160A when I'm driving?

* I know some people like to turn their Daytime Running Lights (DRLs) off for the above reasons, despite the fact that it is less safe and illegal in most states, but they still do it. Why?

MY GOALS:

1) Improve the head light beam strength (lumens) while at the same time reduce the current used to drive them. I think my Halogens use 65W which is 5.4 amps each at 12V.

2) Lower the amp load on the alternator to prolong its useful life, unless you someone can say definitively this is an old wive's tale? ...And is this a mute point since I have installed a VSR (aka Battery Isolator, aka Battery Combiner)? I.e., that makes my alternator always run at 160A?

[jerichorick]

http://www.winnebagoind.com/diagram/...ire_145020.pdf page 1
Trombetta 114-1211-020 DC Contactor
http://www.winnebagoind.com/resource...go_Catalog.pdf page 77
https://www.irv2.com/forums/f54/mom-...go-322534.html
file:///C:/Users/Rick/AppData/Local/Temp/04-Horizon-bro.pdf

[cbeierl]

Originally Posted by jerichorick

http://www.winnebagoind.com/diagram/...ire_145020.pdf page 1
Trombetta 114-1211-020 DC Contactor
http://www.winnebagoind.com/resource...go_Catalog.pdf page 77
https://www.irv2.com/forums/f54/mom-...go-322534.html
file:///C:/Users/Rick/AppData/Local/Temp/04-Horizon-bro.pdf

Rick, that last file is local to your PC and won't be accessible to anybody else!

[Goodspike]

Originally Posted by cbeierl

Rick, that last file is local to your PC and won't be accessible to anybody else!

Well, that assumes you haven't hacked into his computer!

[jerichorick]

Originally Posted by Goodspike

Well, that assumes you haven't hacked into his computer!

Woops!
Thanks,

[DavidM]

I am a bit late to this thread, but I have extensive experience with alternators charging house batteries on boats which have exactly the same issues. And FWIW use of a VSR is very common on boats and an ignition triggered solenoid (the BIRD) is not used ever.

So I think you recognize the charging issue- if the battery demands it, the alternator will supply it- up to a point.

You may see near the 160A rating less any chassis loads which can be significant particularly on newer engines, if you have a large battery bank (you do) and it it is well discharged. Being well discharged means the battery puts a low impedance on the alternator allowing lots of current. But after a while the alternator heats up and doesn't put out its rated current any more. Also the batteries get charged up after a while, the impedance rises and the current drops.

Recognize that RV engines have a fixed output voltage alternator, usually, which limits current unless the impedence is very low. I say usually because "smart alternators" have come along in recent years and I don't really know how they react.

But if you don't have a smart alternator then if you really want to charge fast, consider a high output alternator with an external regulator which will drive the voltage higher, about 14.5 V for faster charging plus it has heavier internal wiring and cooling which lets its output stay high even when it gets hot. Balmar makes these but they aren't cheap, at least $1000 for alternator and regulator.

I know nothing about LED lights but the halogens have long been the gold standard.

David

[imnprsd]

Are you saying a 160A alternator will put out 160A all the time? ...And the internal voltage regulator (inside the alternator these days) acts like a "kill switch"... and will open the circuit... based on resistance or some other value of the battery/load?

[DavidM]

Originally Posted by imnprsd

Are you saying a 160A alternator will put out 160A all the time? ...And the internal voltage regulator (inside the alternator these days) acts like a "kill switch"... and will open the circuit... based on resistance or some other value of the battery/load?

If you are asking me, based on my post above, no.

The alternator is regulated to a fixed voltage. It also has a rated output capability (160 amps in this case) that drops with heat and to a lesser degree rpms. This combination of effects means lots of current is supplied when the batteries are well discharged and present a low impedance. But when the batteries approach about 75% charged, then current is reduced because the impedance of the batteries increases.

For the most point you can replace impendance with resistance in the above paragraph but I use that word because it is dynamic, not a fixed value like a resistor.

David

[imnprsd]

Okay... let me see if I understand:

The voltage regulator... regulates voltage in the general range between 13.5 and 14.5 volts.

...And the alternator will vary current (amps) depending on the loads.

This includes every installed accessory and of course the headlights.

...And if I remember what the Amp Meter looked like in my Dads old '65 Chevy Truck the meter would register current going into the battery (+) and the current leaving the battery (-), which is why I would see the gauge bounce when dear old dad started the engine.

And we all know that when you run an accessory (like a radio or a light) without the engine running, that accessory will take amps out of the battery for a period of time. Hence what we call "AH" (amp-hours).

And if you deplete your battery of AH you are saying the battery internal resistance (impedance) will get lower, and that means the battery internal resistance gets lower, which means more current can flow into the battery when the alternator is running... and the result is a higher "+" indication on the Amp meter.

...And as the batter fills up the internal resistance will increase making it harder and harder for the alternator (or other charging source) to recharge the battery; and the amp meter will drop from max current change to minimum current charge (i.e., amp charge).

So in a car (or old truck) the amp meter would read a maximum of 45-60 amps when the battery is low...

...But in an RV if I hooked up an amp meter to a low battery, what do you think the maximum current would read if my headlights were on and my battery voltage was in the 12.3V range? ...And I have a 160A alternator? ...With it read 160A? ...Is that possible?

Note: I picked 12.3V because that represents a battery with about 40% State Of Charge (SOC).

Why did they take the amp meter out of most cars and RV's... decades ago? Did the gauge cause more trouble than it was worth?

[DavidM]

Your explanation is mostly correct but let me correct a few points:

Most chassis alternators have a fixed voltage output, somewhere between 13.5 and 14.0 depending on the alternator. Sophisticated externally regulated alternators vary their voltage with their charging algorithm and usually peak out at about 14.5 which helps keep the amperage high when the batteries get full.

I don't know where you got that 12.3 is 40% SOC. SOC means how much energy is left. Trojan publishes a very comprehensive Battery Users Guide (google it) and they say that 12.3 volts (resting at least for one hour) is about 65% SOC. At that point the batteries internal resistance is rising and I don't think most fixed regulated voltage alternators will push a lot of current, maybe 0.1 C, C being the 20 hour amp hour rating of the batteries.

If the SOC were down to 25% or about 11.75 V then I think a fixed voltage alternator might push closer to 0.2 C.

So the total amperage from a fixed voltage alternator depends on SOC and the C of the battery bank it is connected to. And it is also affected by heat in the alternator (high temps mean less amps) as well as voltage drop in the wiring.

Everything said above assumes big wire such as connecting jumper cables from the chassis alternator to the house battery bank. Many RVs are built with small wire that causes a voltage drop which can significantly reduce alternator supplied current to those batteries.

Finally to try to answer your question. You have 430 Ahs of house batteries, or a C of 430. So with the batteries low you might see 0.2*430 = 86 amps. That is very consistent with what I measured with my boat with the same battery bank but with a high output, externally regulated alternator rated at 120A. At low battery SOC, a fixed alternator voltage doesn't matter much.

But as the batteries get to 80% SOC it does matter and you will see less than 0.1C maybe 25 amps and probably less due to wiring losses.

Finally there are two things that you can do to significantly improve amperage output:

Increasing the wire size from the chassis alternator to the house batteries will help. You usually have at least 10' between the two and increasing from #6 to #2 wire will cause the voltage drop to go from 0.4V to 0.16V at 50 amps.

The other thing is replacing your existing alternator with a high output, externally regulated one, but it won't be cheap- maybe $1,500 for a 160A alternator and regulator. Balmar and others make these.

David

David

[imnprsd]

Thank you DavidM for commenting and putting things in perspective for me.

This maybe one of my posts where I am guilty of over thinking things a bit too much.

To recap: I started this thread thinking I might be able to reduce the amp load on the alternator by installing an LED headlights, but this does not seem to matter to me any more.

I hope these conclusions are correct?

* Alternator useful life is not dependent on amp load.

* Installing LED headlights will draw less current (amps), and are definitely the way to do for newer vehicles, but for us older RV owners these LED light bulb do NOT have any other benefits, may not provide a better beam of light... when compared to installing a Sylvania's Halogen "Ultra" light bulb. Plus the Halogen "white light" is a truer white I like better.

* In theory, I considered that if an LED headlight drew 10A each bulb (vs. 55A from the Halogen bulb) that my alternator would send more amps to the house battery to recharge it faster? ...And I still don't know if this is true? ...But I do know I drive myr RV (typically) for 5+ hours per day so this point is mute since that's plenty of time for my 160A alternator to charge my house batteries on the road with the Halogen bulbs installed.

* And I don't know about you, but I don't like the "LED blue hues" in those headlights I see on the highways (traveling in the opposite direction).

* Some LED headlights with their heat sinks will not fit and/or have melted wire harnesses. So it is this latter fact that bothers me the most even though some will say they have worked this problem out with LED headlight bulbs.

* If a 430AH house battery bank only receives ~86A from a 160A alternator (based your .2C numbers above), then it really would not matter if I installed a 180A alternator 2 years ago when I had to replace my alternator.

Note: I lost my alternator shortly after my plastic radiator over flow tank cracked at the seams. This allowed anti-freeze to get my alternator wet and I think those diodes in side do NOT like anti-freeze. So if you know you have a water leak going on, you need to address this ASAP. Moreover, as a preventative measure, and tip, to make sure my (your) new (old) plastic radiator overflow tank does not split at the seams again, I used clear epoxy over the seams to reinforce them. And now I am sure they tank will not split again!

[Mongobird]

In my experience, alternator output impacts useful life, and in particular brush life.

I have another application with a diesel motor connected to a 120A alternator, internally regulated. Normally the draw is 90A, and I replace the alternator (or brushes) about every 900 hours, like clockwork.

I recently pulled a LN 2824-LC alternator from my 2004 Meridian, and have not gotten a chance to post-mortem it, but my guess will be brushes. At least on that alternator, brush replacement is facilitated by the design.

Also, if you are assuming a 55A draw for halogen bulbs, you might consider that they are typically 55W, not 55A.

One final thing, a clamp on DC amp meter is useful for taking measurements. May be unhandy rolling down the road, when one wants to measure charge to the battery, but sure is useful stationary. I have two. The nicer one is limited to 400A, and the bigger one is good for 1000A. The bigger one is helpful is starter diagnostics, at least for smaller engines than they propulsion engine on a DP.

[DavidM]

Mongobird is absolutely right. Long term heavy current affects qlternator life, mostly diodes but also windings possibly. A high output alternator such as Balmar's are designed for long term heavy current but even these throttle back current when their temp sensor sees 180+ F to about half of rated output for better life.

These high output alternators are built with heavier windings, better cooling fans and heavy diodes.

Given that you have to throttle back current output on one of these to half of rated output for decent life, that tells me that a standard alternator needs to run at maybe 1/4 of rated output for decent life. This was confirmed by one video I saw where a standard alternator's windings fried at about 100A.

David

[Mongobird]

I would exercise some caution in extrapolating one alternator's behavior to another, and consider it just anecdotal information. The 120A Bosch alternator I referred to in a previous post was tested at 130 amp, in normal engine room ambient temps. After about 800 hours, the brushes failed. I think I have changed out more than 20 of these alternators over the last 20 years or so, and all of them have been brush failures. Not diodes, not winding failures, not even bearing failures.

The engine room for this test was controlled between 180 and 200F.

Because alternators are designed with different product goals in mind, everyone's mileage may vary.

[DavidM]

You obviously have more alternator experience than I do. And yes my example was one anecdote, but accurate AFAIK.

As always YMMV.

David

[Mongobird]

Originally Posted by DavidM

As always YMMV.

David

There are just wide ranges of alternators and their service. For example, a Hitachi 30A alternator on my Ford compact diesel tractor, is still running after 3000 or so hours. I would not have expected that, as it is underpowered for the unit after I lined the outside perimeter with LED work lights. I keep the belt loose on that alternator, to help the bearings last longer. It must work, because I have replaced the water pump three times, and it runs off the same belt (grin).

I have been considering this topic recently, as I am planning on trying to run my refrigerator off 12V, via the inverter, when traveling on the road. There are a range of reports, including from one person who tried it, and ended up with discharged batteries after doing so.

In my 2004 Itasca Meridian, one engine alternator charges the chassis and house batteries, bridging between the two. Since the chassis are flooded batteries and the house are AGM, I am a bit concerned because they both have different charge profiles, and bridging them is less than ideal.

It is important to consider that the alternator is merely a power supply, and does not have the capability to provide different charge profiles. While I have several smart chargers, which can run different profiles, they are consumer units and top out at 25A, not enough for an RV. Ideally I'd like a way to manage, automatically, the different bulk, adsorption and float charge modes, voltages and currents. I have not found anything I can readily use in the RV, which could be dedicated to each type of battery, to optimize charging and reduce battery wear and tear.

It might be easier to go car LiIon retrofit...at least for the house batteries.

[DavidM]

Mongobird:

Here are some thoughts based on your latest post:

I have been following several forms to understand DC compressor fridge's power usage before I finally bought a Thor Axis with an absorption fridge. Various owners have reported between 50 and 100 amp hours daily DC requirement to run the fridge. I suspect that the variations are due to outside air temps and size of the fridges, the 6 cu ft unit drawing less than a 10 cu ft one.

These observations (yes they are anecdotal) are consistent with my own observations of similar fridges on cruising boats where I had a battery monitor and could accurately measure amp hours used each day. A small Novakool under counter fridge used about 50 Ah and a stand up fridge used about double that.

There is a way to get three step charging profiles, by either buying a high output alternator/external regulator to replace the one you have or modify the one you have to hook up to Balmar's three step external regulator if it is robust enough to handle the extra charging current that the three step regulator will produce.

Sprinter engines for sure and maybe Ford V10s and almost certainly the new Ford V8 E350/450/F53 have what is called smart alternators. The excitation current that varies the voltage and current output is controlled by an engine microprocessor that takes all sorts of engine and environmental inputs to produce the required voltage and current output. Hooking up external batteries without some sort of current limiting device and almost certainly replacing or modifying the alternator and hooking it up to an external regulator will have all sorts of unknown consequences.

For example when I google Balmar alternator and Ford V10 all I can find are companies that will sell you a second alternator package including mountings, no doubt to leave the OEM alternator alone.

Your Meridian with its Cat? engine may have a more basic alternator as that engine is probably fitted on all sorts of marine, agricultural and construction equipment as well as trucks and MHs. So an external regulator may be a possible solution for more DC power from it.

And with Lion batteries you really need a fixed 14.5 V output from the various charging sources. A PD 91XXAL converter will do that and so will some solar controllers and several B2B chargers and BMI systems that hook up to your alternator.

David

David

[Mongobird]

Thanks for the data points. The LN 2824-LC alternator is indeed basic, but allows remote sense, and the output is floated relative to the case.

Gotta run at the moment, but will re-read later when I can look up what you mention and take it all in.

[imnprsd]

Mongobird: Thanks for pointing out my headlight power typo. Yes, 55W is correct (and 65W High beam). So lets say the high output "Ultra" bulb will use ~5A/bulb in a 12V system. And since I have 2 light bulbs that's ~24A.

Specifically, do you gentlemen think it makes sense or NO SENSE to install LED Headlights for the expressed purpose of reducing the load on the alternator?

On the road, my two largest power draws are the DRL and my residential refrigerator. So I started this post trying to find people like you who can give me and others advice on how to extend the life of their alternator?

So maybe I should have asked questions like these:

* On a diesel or gas engine, do they make a alternator "clutch" pully wheel and has it been proven to extend alternator and belt life?

* Does it makes sense to install LED Headlights for both function and to extend alternator life?

* Can I loosen my alternator belt to extend alternator life, or is this more problematic over time? Note: My alternator failed at 75,000 miles, but that was over 10 years when I did not own the coach.

I drive about 7,000-9,000 miles/yr so I wanted to explore this subject to avoid another alternator service in 8 years or so. ...So again, maybe I'm over thinking this subject, but I do it, and write about it, so I can better understand how my charging system works?

For example:

* If I have solar power on the roof, can I install a "power monitor" that will give priority to the solar cell current over the alternator current? ...My solar controller will put out between 0 and 18A, depending on the sun variables?

* I have a residential refrigerator and it runs on 1A-120V or 10A-12V, which after inverter efficiency loss draws more like 12A... plus several startup spikes over an average 5 hour drive, so I call that 15A on average. (Or ~100A over a 8 hour period on the road.)

Note: I am mindful that I am talking about engine loads off the 12V chassis battery bank; and coach loads off the house batteries; but since these two energy storage source are "combined" in my coach via a KeyLine VSR, I think I can look at alternator loads as a combination of both chassis and RV loads.

* Are you guys are saying my 160A alternator maybe capable of delivering 86amps to my 430AH house battery bank, but is more likely running at 1/2 power, or 1/4 power?

* How many amps does it take for my diesel engine to operate?

[Mongobird]

Changing to LEDs to reduce headlight power costs is not the lowest lying fruit. I would not do it first-order.

Do not run your belt loose. I probably should not have said what I did. The tractor belt has very little power, and is a V belt. Your alternator belt is most likely a serpentine belt.

There are clutches for alternators, but usually they are overrunning clutches. But the type you are referring to, you will generally not find. AC compressors have such clutches, but it is better for your alternator to just be spinning, rather than clutched.

If your refrigerator draws 12A at 12V, then I say you can just go for it. That is like running a heater blower or an AC blower on high. Not going to sink the ship.

The actual draw of charging AGM and flooded batteries is not simplistically addressed here. Your alternator is a power supply, and it will supply power which will charge the batteries. It will not always be ideal for rate of charge, or for life of battery. Someday we will have really smart chargers and controllers, but they are rare today.

As for when the next alternator needs replacing, I would say that you have taken a first order look at things, and it have a reasonable approach. 15A for lights, 15A for other accessories like wipers and blowers, and 15A for your refrigerator. Don't expect that your batteries will be at 100% after 8 hours of driving. Even if you don't run the refrigerator that might not happen. Just take what you get.

Similarly, with respect to when your next alternator will come into your life, there are many variables, including what alternator builder, and who didn't sleep the night before they built yours. You can't control all those things, and you can't know all the variables. So run the beast, be careful with it, like you are investigating here. If the alternator fails down the road, so be it, and move on.

There is a book on RV Electrical Systems, which I found at the library, and scanned through. It is dated, but you might find it interesting. I actually looked at an electronic copy, but it is also in print. "RV Electrical Systems" by Bill Moeller.

I don't know about your engine, but most that I am familiar with draw between 1 and 5 amps.

Finally, normally, with a alternator, it is seldom putting out maximum power, especially charging batteries. So if you are drawing 60A for your systems, do not think that you are putting the full balance into your batteries. It is likely less.