2GM20F Idling/Battery Charging

[200grandprix20465]

I am trying to find the best RPM to run my 2GM20F to charge the batteries?
We quite ofter spend a couple nights in a cove and I need to charge my batteries after a long night.
The alternator registers 14v at 1000rpm so thats not a problem. I usually set it for 1100-1200rpm but I think that is to slow and don't want to harm the engine.

 

[JoeWhite]

Here is what I would do. If you are on the hook ir mooring - put in reverse and let it idle - no need to rev up the engine - if the voltage is more that 12.5 volts - it is charging. If you are at a slip then use the shore power.

 

[Witzend]

This is always a bad idea. Not sure what engine you have, but it will probably have a damper plate isolating the transmission from torsional vibration. The design of these plates work best under load, otherwise they chatter back and forth causing wear not only where the springs contact the edges of the plates, but also the contact points between the damper plate collar and the transmission input spline shaft. Ultimatly striping out the collar and damaging the input spline. Also, small diesels don't develop enough heat to support complete combustion when not running under load. The result of this can cause moisture within the fuel/air mixture to condense and end up degrading the oil. I suspect incomplete combustion may also tend to clog up the mixing elbo as well, but that is just a hunch. Get a solar or wind generator to supplement you charging requirements, or at least put her in gear and put some load on her.

 

[redhead78]

The good for your engine these are not like the big rig v-8 diesels, extended idling is not good for the newer smaller engines. osult your manual. ..Red

 

[sailingdog]

I would highly recommend you get and install a battery monitor and figure out what your electrical usage is and then upgrade your house bank to deal with it properly.

 

[Maine Sail]

I would highly recommend you get and install a battery monitor and figure out what your electrical usage is and then upgrade your house bank to deal with it properly.

Ditto...

The Victron BMV-601 is under $200.00 at Jamestown Distributors. 14+ volts does not tell you much about the amperage.. Idling an engine with minimal load can glaze the cylinder bores if you are not careful. Without knowing the actual state of charge you may be idling your engine without need..

 

[druid]

Depending on how long you stay on the hook, a bigger battery may not help (if you're using 100 A-H per day, you have to put it back, no matter how big your battery is). The 2GM20F isn't exactly a "new" style diesel, but it doesn't like idling.

But a REAL eye-opener is putting an ammeter in series with your alternator: I'd guess at around 1200 rpm it might start at 25 Amps or so, but quickly drop to maybe 10 Amps. So that 100 A-H will take TEN HOURS of idling. Look at getting a charge controller that will override the regulator and pump in at least 25 Amps or so (depending on how big your batteries are...)

druid

 

[Stu Jackson]

Small Engine Mode for Regulators

You may be interested in this post, scroll down to Reply #20, and in reading the entire thread starting on page 1: http://c34.org/bbs/index.php/topic,4454.msg27149.html

This explains what Maine Sail meant about "idling your engine without need..."

 

[sailingdog]

Druid—

The point Maine Sail and I are trying to make is that having a battery monitor will allow the OP to figure out what the actual electrical usage is. Once he knows his actual usage, he can plan his battery bank size to accommodate his usage and what his recharging regimen is going to be.

For instance, if he mainly weekends with the boat and needs to have three days of cruising capability between recharging at the dock using his shore-powered charger—knowing his actual usage lets him size the battery bank appropriately and also check the actual state of charge—rather than guessing and running the engine when it is unnecessary.

 

[Stu Jackson]

I partially agree.

What comes OUT is easy: do an energy budget. You don't need a montior to do thast math.

It's what goes back IN that is harder to figure because of battery acceptance, which is NOT linear, like the loads when they are removed from the bank. Here: http://c34.org/bbs/index.php/topic,4787.0.html

That's really where a montior earns its cost. Very worthwhile.

 

[sailingdog]

Actually, I've found most boaters are surprised when they install a battery monitor because they either use way more or far less electricity than they estimated to be the case... and as such, all of their electrical system sizing is way off.

I partially agree.

What comes OUT is easy: do an energy budget. You don't need a montior to do thast math.

It's what goes back IN that is harder to figure because of battery acceptance, which is NOT linear, like the loads when they are removed from the bank. Here: http://c34.org/bbs/index.php/topic,4787.0.html

That's really where a montior earns its cost. Very worthwhile.

 

[Stu Jackson]

Actually, I've found most boaters are surprised when they install a battery monitor because they either use way more or far less electricity than they estimated to be the case... and as such, all of their electrical system sizing is way off.

Could be. Not everyone was good at math in school!

 

[sailingdog]

Between that and only having a vague idea of what stuff actually uses... and how much they actually use the stuff...

Could be. Not everyone was good at math in school!

 

[sailaway78]

Battery Monitor

For the price of a battery monitor, you could just about install a small solar panel and regulator. A 80 watt or so panel and regulator, would probably put more into the battery than idling the engine for a few hours, providing the sun is shining.

 

[Chuckbear]

For the price of a battery monitor, you could just about install a small solar panel and regulator. A 80 watt or so panel and regulator, would probably put more into the battery than idling the engine for a few hours, providing the sun is shining.

But you would still not know what the state of your battery and charge is without the monitor. More systems to charge is even more of a need to monitor conditions and status. Chuck

 

[redhead78]

I am a weekend cruiser, just radios, some lites ( I like and use candles), Small GPS, occasional auto pilot,and with my old engine very poor charge system. I also installed a small Sunsei solar panel, it trickles all week long.I ordered the 100 amp high output alt with my new engine. This should help also. Red

 

[MrBee]

Like the rest of the answers, I don't know exactly what the best RPM would be to run the motor. It IS best to have a load on it. I would just keep it running at around 1200. Check the Batteries after engine shut down and after letting them rest for an hour and see what the reading is. Do this after few nights and keep track ,after running the motor for a different length of time and you should be able to figure about how long to let engine run to top the batteries off.

Brian

 

[Maine Sail]

Check the Batteries after engine shut down and after letting them rest for an hour and see what the reading is. Do this after few nights and keep track ,after running the motor for a different length of time and you should be able to figure about how long to let engine run to top the batteries off.

If it were only that easy.:cussing:

Measuring battery SOC via volt readings can be quite inaccurate when out cruising. This is probably why the historic battery life/cycle life in marine applications is soooo short.

I have many hours of bench testing to try and figure out what the magic bullet is and the only voltage measurement I have found is a 12-24 hour resting period with no voltage/amps in or out.

This would mean physically disconnecting the batteries on the boat and letting them sit for 12+ hours to get a close to an accurate reading.

I have even tried multiple load tests, by applying varying loads to them, to see if a specific load can get you close to the 24 hour rest voltage. I found the closest I got, with varying loads, for varying amounts of time, was to be within 12+% of the 24 hour rests actual number..

Compounding 12+% variances each day could add up and lead to a short battery life. On the other hand not understanding how to use a battery monitor can also result in reading discrepancies and they can be just as dangerous to the batteries if not used and synced occasionally..

Measuring Battery State of Charge (LINK)

 

[MrBee]

Thanks Main Sail, I have seen that posted or on your web site before....and in a perfect world we all would have everything we want and all the time to play and learn to use it. Most of the time that's not the case.
When I have time AND money to do all the right things I look to you and a lot of the guys around here for help but just like boats, the excessories we use are a compromise of cost, use, need,..

Chuck, I didn't see Larry's post but do see his point. Not all of us can just look up what would be best and Write the check. Most of us have to compromise. Maybe you think that those of us that can't have it all just perfect should stay home.
My personal situation is that rather than spend all the $$ on all that monitoring equipment I can buy a hole bunch of batteries over many years. I do know it is best for the motor not to be idled for charging bu after money for a boat, Slip fees. and all the stuff that HAS to be payed to just to own it, I only have a limited budget left each year to spend on "Other" stuff.
Example.. I bought a Wheel pilot for this coming season. Since my situation dictates I sail alone OR only get out one or two times a month, maybe three, that is more important to me than monitoring my batteries...Or I could get all the good stuff to monitor my batteries, Gee I guess I could hang out at the marina and watch battery use.
Not trying to be rude or even say that the person asking the question has the same situation as me. Just that time and again I see answers to questions that fit the "If I could do anything I want no matter the cost" this is what you should do type of answer. That answer fits less of us that you might think. I know Idling is not that good for the motor, but at this time it is what I have to do
Some how a simple question of the " What's the best rpm to idle the engine at to recharge batteries " Got turned in to a need to spend many $$ so you know how long to charge......

Have a nice day and keep those good answers coming.

Now if someone could actually answer the original ?? What IS the best RPM to idle the engine for battery charging ???

Brian

 

[Maine Sail]

Now if someone could actually answer the original ?? What IS the best RPM to idle the engine for battery charging ???

Brian

Brian,

There is no one easy answer for that.

You need to be able to see amps in at a specific state of charge to know which RPM is best for your alternator and engine/pulley ratio. A digital clamp on, DC, digital volt meter will tell you the amp output at a given RPM.

It would be best to do this, with the clamp on DVM, at or close to 50% state of charge so the acceptance was not the limiting factor. Perhaps you could borrow a DC clamp on DVM.

At 80% state of charge or higher, depending upon the bank size and alternator size, you may never be able to put in any more than what the alt could deliver at idle anyway because of the low acceptance of the batteries. Running it at a higher RPM would be wasteful and also apply a very minimal load to the motor which we know is not necessarily the best practice.

Trying to charge your batteries back above 80-85% state of charge with an alternator is painfully time consuming and slow and not very good for the engine.

Getting from a 50% state of charge back to 80% is what most cruisers look to do and is quite doable with an alternator.

To put in lots of amps, at say a 50% state of charge, at idle, with most factory alts, will not supply the full amperage into the typical house bank. For example, a Leece Neville 72 amp alt with internal regulator, the standard upgraded alternator on a Universal M-25, will put out about 27 +/- amps at 1000 engine RPM that is considering a 2.5:1 pulley ratio and a alternator shaft speed of 3000 RPM.

If you have a small 100 Ah battery at 50% SOC 27 amps is likely more than it can even accept, but if you have a 300 Ah bank it could accept a lot more than you are actually feeding it.

As I said not an easy answer. We do know that idling does not help your engine though and we also know how expensive re-builds are.

I find it interesting that people condemn a $195.00 battery monitor as costing them money, the whole boat costs you money. I have found that a good monitor tends to actually save people money, though over the longer haul, by preventing a needless upgrade or making batteries that used to last 2 years now last six or seven.

I run a 50 amp stock alternator on my boat because I know that with my solar panel and light consumption/use I rarely if ever dip below a 70% state of charge. My alternator is rarely even required to put out even close to its rated amps. Without a monitor I surely would have upgrade to a big ole alternator $$..