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Generator Alternator

What does the alternator do on the generator. Being it is a generator, and the bus has numerous batteries including a generator on the engine itself, I am confused as to what that little alternator really does if anything. Can anyone shed light on this?Huh

2002 Newell Coach 621. The harder I work, the luckier I get.

The alternator recharges the house batteries (which the generator uses as a power source for starting). If you are parked for an extended period of time, the generator's alternator will recharge the house batteries during the time the generator is running to help prolong the time you can live off of your house batteries when the generator is shut down.

By turning on the merge switch, the generator batteries would also slowly recharge the engine batteries.

Michael Day
1992 Newell 43.5' #281

Michael is quite right but i can expand a bit. When generators are purchased from a vendor they include a starting battery recharging alternator. doesn't matter if it is an Onan, Kohler, Martin, Power Tech, or most any other company, they will have an alternator unless specified otherwise at time of purchase.

Our electrical systems are fairly complex for most non-electrical individuals. We have house batteries and main engine starting batteries plus inverter chargers and on older Newells, convertors (simply power supplies). Some Newells use the house batteries and others the main engine batteries (I have seen both connections) to start the generator. If the engine batteries are used, the alternator helps keep the engine batteries charged as does the main engine's alternator. If the house batteries are used the alternator will keep those batteries charged however, sometimes the alternator competes with the inverter/charger circuitry and creates problems. The generator's alternator is easily disabled by unpluging the signal wire if that is an issue.

Gordon Jones

What problems happen when an alternator competes with invertor ?

Larry, Hedy & Benny Brachfeld
2003  Coach # 646
2 Slide, DD
MINI Cooper Clubman S
MINI Clubman , John Cooper Works Rally Edition # 3 of 70
Monster 1000 Watt, Electric Skateboard
Yamaha Golf Cart painted Kawasaki Green
A Coach driveway with a shade structure and swimming pool 
A Pueblo Home on the Border

Every situation is different with the wide assortment of electronics but from experience (my own) , the generator alternator regulator would turn off when the inverter/charger peaked the battery voltage and as soon as the inv/chg turned off the voltage would fall low enough to turn the alternator regulator back on before the inv/chg. The end result was a cyclical on-off sequence that you could easily see in the 12V lighting. I unplugged the alternator excite wire and let the inv/chg do all the house battery charging. My gen was connected to house batteries.

Another experience was when the gen was connected to the engine batts and both alternators were charging if the gen was running while the main engine was running. That scenario took out the main eng alt regulator as both regulators were trying to control voltage.

Gordon Jones

I asked the techs at Newell this exact question in June 2015. Here's what I got...sorry if I go a little off topic but I think it's important information.
They said the alternator on the generator is just an expensive idler pulley for the generator belt system.
The inverter / converter / charger keeps the house batteries charged and provides way more charging capacity than the little alternator.
From a pure efficiency standpoint, I suppose it would be better to have an alternator charging the batts because it would convert mechanical energy directly to the required power type instead of going from mechanical to 120 AC then to 12 would, however, mean more hardware (bigger alternator and switching system between inverter-charger and alternator) and the efficiency benefit likely would never pay off (like solar).
There is also a trickle charger (echo brand?) that steals a little current from the house batteries to maintain the start batteries even if the merge switch is not "engaged".
***They caution STRONGLY against using the merge switch while the drive engine is running. They said it's very taxing on the batter isolator which directs the main engine driven alternator's charge to the right battery set.

Jonathan Shetler
1999 Newell 510
Ft Lauderdale, FL

My engine only has one belt which driver the A/C compressor and the alternator.  Therefore if that belt should break I would start the generator and put the merge switch on being it would be the same as plugged in.

Chappell and Mary
2004 Foretravel 36 foot

I'm sure Gordon has a better idea but Newell has told me the best thing to do is keep the batteries merged if the engine or the generator is running or shore power and unmerged only when dry camping..

Marc Newman
Formerly Newell 422, 507, 512 701


Marc, I was told by Newell that batteries are auto merged whenever the 8V92 is running. They also recommended merging with switch whenever boondocking if generator is running then unmerge when you shut off generator. I always merge when hooked to shore power to make sure engine batteries stay charged. We also always run generator when driving but don't use manual merge switch. Our coach is a bit older than yours so you may have a bit more modern merge technology than us.

Beware that if you keep the batteries merged when the coach is parked (and you're not camping) you will find all the batteries including your start batteries dead if the coach power is interrupted without you noticing. This happened to me when the coach was parked at the house.
Chappell, I'm living the scenario you AC compressor went bad so I removed the single belt which also ran the alternator. To keep the batteries up they're all merged and generator must run when we aren't plugged in. This is an exception to the merge rule only because the alternator isn't running.
In a fully functional coach, the batteries are "merged" when running the main engine using a device called the isolator. It looks like a little car stereo amplifier (aluminum block with heat dissipating fins) and has 3 big wires coming to it. It is a part that all motorhomes use not just Newell (although they use a huge one). It is the part directing where to send the alternator's power. The guys at Newell said you'll eventually burn it up if you run your engine (and alternator) with the battery switch in either of the two merge settings.
My little echo charger to keep the engine batteries up by stealing from the house batteries (without merging) is located in the drivers side bay with vacuum and near the inverter. I know other coaches have them bc I read a thread where the folks were discussing them and less expensive alternatives. It was a part of the original build, not aftermarket.

Jonathan Shetler
1999 Newell 510
Ft Lauderdale, FL

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