Generator charge output - what is normal?

I recently installed the very clever Trimetric battery monitor. I love it. I just installed my Genturi so took the opportunity to run the generator for a monthly 15 minute maintenance run.

Now I can read the generator output to the batteries - very nice.

It's 2.2 amps, at 13.1 to 13.2 volts.

The converters charger only does half an amp which confirms the generator's output certainly bypasses the converter's charger.

So clearly the generator has an alternator which puts out at least 2.2 amps perhaps this is representative of an acceptance stage, since my batteries were at about 12.5 volts or 92% before charging. The generator is a 4000watt and that is 33.3 amps. Perhaps I will flatten the batteries to 50% and then read the gen output.

What amperage would you expect to see of your generator output charge to the batteries? Is my reading normal?

I had assumed that when I soon upgrade to a 40 amp True Charge, then I will charge at up to 40 amps from the generator if I have things wired correctly. Do I have that right?

Thanks.

Genturi sidebar:
I had to subsequently order the bent elbow for my downer exhaust tube. It's a bit too much much of a bend now, it slopes towards the coach. I'll bend it tomorrow, slightly, with a couple closet dowels, without pinching it. It does seem to hold down the exterior racket, by a surprising amount. It definitely reduces the noxious fumes at ground level outside the rig. It has quite a column of air coming up the tube as you check it from the roof. There were zero noxious fumes in the rig after 20 minutes, even though I had roof vents ajar. Compares favorably to' before' when it really stunk like a lawnmower in the rig. It is a slick unit. I opted to buy it to save time - considered DIY. I saved a LOT of time. It was only $100. I recommend it. After playing around with it, I just might gain the confidence to run it during sleep - provided active alarms. It seems it would work fine for that. Even so, it greatly improves the liveability of that generator, which is quite a nasty thing.

I would be very surprised if your onboard generator has any direct 12v charge output at all, let alone wired to your house batteries. Is it the 4KW Onan? Or is this an aftermarket generator? Normally the generator pwoers the coach and the coach's built-in charger does the battery charging, just like when on shore power.

When you upgrade the onboard converter/charger to the True Charge 40, it would charge at up to 40A. Generally, though, the amp rate will be much lower, depending on the state of charge of the batteries and any other loads while charging is in progress. Once the batteries are fully charged, the amp rate would be tiny, probably under 0.5.

I think what you are reading is the battery input voltage to the generator. I too have never heard of a generator that puts out 12 volts.

Portable gensets often have 12v power plugs for direct feed (not really a charger), but permanently mounted gensets in motorhomes rarely do. If ever.

No, I don't think you do have it right at all!!! (Sorry!!)

I don't understand why you think  running on the generator results in better charging as you seem to say. Generators installed in motor homes do not have battery charge functions like the add-on portables do. They simply supply 120V to the motorhome just as if you are plugged in. In other words, the same Converter/Charger is still maintaining and charging the batteries as before as well as supplying the other 12V needs of the motor home. The only advantage may be that the 120V Voltage output by the generator may be a bit cleaner than that from the plugged in supply, due mainly to condition of the pedestal, the connectors the cord, the load in the park etc.

The generators output is at 120V, and has no direct relationship to the converter/chargers output at 12V. The generator outputs only what is required by the load, up to it's maximum of 4000 watts or 33 amps in this case The converter/chargers charger section's output is similar but the 12V DC output current (amps) is in response to the state of charge of the battery bank, again up to the maximum designed output of the unit. Its 120V INPUT or draw in amps is part of the load presented to the generator and will vary depending on the output required for charging as well as the rest of 12V load presented by the motor home.

The difference in charging amps observed is much more likely due to the state of charge of the battery bank at any given time. What you are reading depends a lot on how and where the amp reading you are seeing is being measured too.

That is not to say that there would be no benefit to adding an intelligent charger such as the Xantrex True Charge (which is available in 4 models with different output capacities). There is!! I do not understand, however, why adding this kind of single purpose charger as opposed to an intelligent converter/charger would be much of an advantage here except, perhaps, in initial cash outlay.

Perhaps consideration should be given to Xantrex's other lines of intelligent converter/chargers or those of Progressive like the 9240, or the other quality brands with sufficient outputs to service the whole coach and charge the batteries properly,  by replacing the existing converter. The existing unit may be one of the  "stupid" units often found in many vehicles and that are often responsible for overcharging the battery bank..

You really don't need a huge charging capacity in amps, as in your example of 40 amps. That rate does not last very long. It will drop down quickly as the battery charges. In fact, charging at very high amperage rates can do a lot of damage to a battery bank by excessive heat generation, evaporation of the water and warping the plates as a result. High rates are usually only applied when a fast charge is required, not usually the case in a battery bank such as this. Slow and steady is good.... and the intelligent inverter/charger has the smarts to do this correctly. It is highly unlikely your existing wiring could handle this kind of charging amperage in any event.

HTH

If this is the generator installed on the motor home running the generator .. Should be the same as plugging into shore power.. Save for .

STARTING the generator.. Uses those same batteries.

seilerbird said:

I think what you are reading is the battery input voltage to the generator. I too have never heard of a generator that puts out 12 volts.

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No??? Many generators can have a DC output. Remember the old cars? They were all 6V DC output generators for the most part.... The generators we are referring to here are engines coupled with alternators and put out 120V AC as you say,  referred to as Gen Sets or Generator Sets, but we most often refer to them as simply 'generators'.

Very helpful inputs friends. Thank you.. I don't yet have a 30a shorepower plug converter to judge the difference between amperage from generator and shorepower to continue to ID what happens in my systems. Looks like the plug is next!

Yes it's an Onan 4kw onboard install.

Several large cables (size 4, battery cable size) go from the bowels of the machine to a common pair of posts (+ & -) behind the hood. I discovered one of these cables hanging loose, victim of a busted large ring terminal. It is unclear when it is live, and where it wants to be connected. It apparently wants to connect one of those posts to one of the batteries. That is going to be a challenge to correct. I'll start with the DVM & rubber shoes. I have it taped off for now.

Part of the upgrades & updates will be proper cabling. Finally there will be solar panels & controller. 

The reason I have made incorrect assumptions about generators is this is my first exposure to the beast.

I plan to install three Group 31's for ~375 aH capacity for winter use. I want a 40a charger to reduce charge time when off the grid. Generator will bulk charge (goal being <1 hr/day), solar will complete acceptance and float phases.

Thanks again. I appreciate the expertise.

In summation from your feedback, the shorepower and the generator are redundant systems where each runs to the batteries via the converter. Consequently the batteries should charge at the same rate from each source. 

the shore power and the generator are redundant systems where each runs to the batteries via the converter. Consequently the batteries should charge at the same rate from each source. 

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Yes, more or less..... Shore power is usually considered the primary source though with the generator as a backup or alternative source.

Several large cables (size 4, battery cable size) go from the bowels of the machine to a common pair of posts (+ & -) behind the hood. I discovered one of these cables hanging loose, victim of a busted large ring terminal. It is unclear when it is live, and where it wants to be connected. It apparently wants to connect one of those posts to one of the batteries. That is going to be a challenge to correct. I'll start with the DVM & rubber shoes. I have it taped off for now.

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Could this point of connection be the emergency start relay (or MOM circuit) perhaps??

The purpose of this heavy duty relay is to enable the house battery to be temporarily connected to the engine battery should the engine battery be too low to start the engine. It also works the other way round where the engine battery can assist the house battery to, for example, start the generator, as a built-in booster, if you will.... It is usually activated by a switch with a spring return (has to be held operated to use) that is located  in the drivers area. In some motor homes, a similar relay is activated when the engine runs and the motor home's engine powered alternator outputting 12V DC will charge the house batteries as well as the engine battery while travelling.

Don't count on solar for too much in the winter in some areas as it will require a large aimed array pointed into the sun over a prolonged period to generate sufficient electricity (and no snow coverage, shadows from trees or cloud cover). Better than nothing but....

Actually.....My 1994 onboard factory installed Onan Emerald II does have a battery charging circuit that is basically a bridge rectifier and a large resister both mounted on the inboard (starter side) right to the engine block. According to the manual it is there to charge the starting battery and (if memory serves correctly) is wired back to the starter solenoid, so while it is not really needed in this application, since the generator supplies 120V to the converter anyway, it does exist.

That is an interesting concept!! So this could mean that the house battery or the engine battery could receive a charge depending on the configuration in any given situation. Was it hooked up and working??

I think it was originally intended for configurations that had a small starting battery for that generator alone though, unusual for an RV but logical in a stand alone setup.

In a proper marine setup, the priority is to the starting battery, so all charge power leads there first till it's full (which takes milliseconds!) then the combiner/isolator switches over to the house. It seems that in a typical RV setup, the alternator charges the starting battery (??) so all charge power is directed to the housebank, except for that which is "converted". (if I have that straight).

Yep I plan to buy a little more solar panel volts than I might need, and I plan to have a little more housebank capacity than I might really need, so that systems will support a winter habitat.

"Why not just get the converter upgrade?," you asked. 
Well, I am thinking about it now, but the truecharge offers battery temp monitoring and desulphating 4th stage. I dont think the converter upgrade products do that. but I may choose in favor of easy install. and the upgrade is actually cheaper. the bestconverter upgrade photos do not show battery cable upgrades (which I would do), which makes the upgrade seem easier than it should be.

Remember there are two charging systems in a motorhome - one that runs off the engine and an independent "house" system that is powered by either shore or genny. The engine alternator gives priority to the starting battery, whereas the independent house system gives priority to the house batteries. In some brands/models of coaches, the house charging system never charges the engine starting battery, while others have a charge controller that handles both with priority to the house batteries.

There are other brands of converter/chargers that offer a 4th "equalizing" stage. And many inverter/chargers have both equalizing and temperature monitoring. But the True Charge 40 is an excellent choice and will do a fine job for you.

Alfa38User said:

That is an interesting concept!! So this could mean that the house battery or the engine battery could receive a charge depending on the configuration in any given situation. Was it hooked up and working??

I think it was originally intended for configurations that had a small starting battery for that generator alone though, unusual for an RV but logical in a stand alone setup.

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The only reason I even knew it was there Stu, was because when I had an issue with my starter I reached around back with the handle of a screw driver to give the starter a whack and hit the rectifier instead (couldn't see either one) When I pulled the Genny out to fix the starter, I found the damaged rectifier also. Even the guys at the Cummins parts counter didn't really realize at first what I was talking about until they looked it up. I haven't ever checked the output voltage as it really isn't needed anyway and everything is working good. I think you are right about it being there for an independent starting battery in a different application

I am curious about the amps to the battery from the PD4645 (or 4655) converter upgrade unit.

1) Can you please tell me how many amps go to the battery at most?

In other words, with a TrueCharge 40, you get up to 40 amps for battery charging. What amps do your batteries get from the PD4645 or 4655?

2) Do you get more charging amps from the 55 amp version, or is the charger performance the same as the 45 amp version?

I apologize for asking way too may questions about this silly decision. I am quite ignorant about RV systems, learning fast.

Sidebar update:
The loose wire that I have under the hood must be for alternator charging of the house bank. The Trimetric battery monitor tells me that the house bank is negative amps while going down the road, but it should be positive amps / charging if working properly.

Every PD converter I have seen can put 100% of its output into battery charging IF there is no other demand. But rarely can a battery accept 45 or 55 amps of charge - it would have to be down to around 50% of charge before those rates would apply for more than a few minutes.

Unlike the old Magnetek 6300 series, the PD 46xx does not have a separate battery charging output that is limited in power. All the power is applied on the output circuit, which does both house power and charging.

PD 4600 series specs:  http://rvpowerpartsplus.net/pdf/Intelli-Power%204600%20Series.pdf

anemic said:

Genturi sidebar:
I had to subsequently order the bent elbow for my downer exhaust tube. It's a bit too much much of a bend now, it slopes towards the coach. I'll bend it tomorrow, slightly, with a couple closet dowels, without pinching it. It does seem to hold down the exterior racket, by a surprising amount. It definitely reduces the noxious fumes at ground level outside the rig. It has quite a column of air coming up the tube as you check it from the roof. There were zero noxious fumes in the rig after 20 minutes, even though I had roof vents ajar. Compares favorably to' before' when it really stunk like a lawnmower in the rig. It is a slick unit. I opted to buy it to save time - considered DIY. I saved a LOT of time. It was only $100. I recommend it. After playing around with it, I just might gain the confidence to run it during sleep - provided active alarms. It seems it would work fine for that. Even so, it greatly improves the liveability of that generator, which is quite a nasty thing.

Click to expand...

When I installed my Gen-turi, the pipe leaned away from the motorhome sidewall a bit more than I liked. I drilled out the two pop rivets holding the bracket arm closest to the wall, and gently bent the other two arms until the pipe was vertically level. I then drilled two new holes and pop riveted the arm in place. It works perfectly, and I'm very pleased with the reduction in exhaust fumes and noise.

I ordered the PD4655 - the 55 amp upgrade, after speaking with Randy, he said just to install minimum 6 AWG wire to the new converter piece and I'm all set. The only feature I'm forgoing with this versus the TrueCharge is battery temp monitoring / compensation. However, the planned solar install will take care of that so I'm not concerned.

THANK YOU for all your inputs. Very helpful. Now I have an easier install, a bigger charger and I spent less money. Thank you.

Let us know how the 4655 upgrade goes. If it is as easy as the install instructions imply.

It was pretty easy! I took a lot more time than a half hour however. Probably 90 minutes. A significant chunk of the extra time was an issue I had with my AC circuit breaker. When I backed the screw out, the old converter wire came out fine, but I could not easily get the new wire into that spot, and it was blind, on the bottom. Finally pried the clamp open and then things wrapped things up quickly & smoothly. A slight bit of metal bending was required in my install; the new converter box flange was not precisely in the right places for screws, but that was easy. I think it is possible to do it in 30 minutes. But then you have to pull all your blade fuses out and re-install, reroute all your 12v circuits...which simply takes time, nearly a half hour itself believe it or not. In summation it was a fun easy project and it's a very neat bit of kit. I love it. I was down to 12.2 V on the housebank. I was immediately charging at 30 amps! I will upgrade the battery feed cables from 8 gauge to 6 gauge and see if I can get that bulk charge even higher (closer to 55 amps) when the batteries are that low. Perhaps 30 amps is all the batteries would accept from a 12.2 volt condition. Put me down as Pleased As Punch