Understanding AUX-START with generator

[beaubeau]

Can someone please help me understand what might be going on here....

It's been a number of months since I used my RV (2008 Allegro FRED). Earlier this year I replaced the chassis batteries. Last year I replaced the house batteries.

Yesterday I decided to start it (it's been maybe a month since I started it) and it was dead-dead. The dash wouldn't illuminate, for instance.

So I hit the AUX-START button and it (reluctantly) started.

Then I decided to start the generator. That too required that I hold the AUX-START.

So far, I think I understand what's going on, but....

When I release the AUX-START button, the generator shuts off.

Why?

[dougrainer]

beaubeau wrote:
Super!
This makes sense, thank you. All except that the generator doesn’t run even if the chassis engine is running, unless AUX-START is held down.

dougrainer wrote:
2008 Tiffin. The chassis starts the Genset. It takes 12 volts continous for the Genset to run. Gensets do not supply 12 volt power once they are running. So, you got the Genset started with the Battery boost button. It takes the COACH batteries to engage the battery boost. So with the battery boost button pushed ON, your Genset started from the coach batteries and the coach batteries supplied the 12 volt power to keep the Genset running. Once you released the Battery boost, the Genset and Chassis side LOST the 12 volt signal. Hence the Genset died. Have you tried the same operation but start the Engine first and leave ON? Then boost to start the genset. The Engine alternator will supply the 12 volts required to keep the Genset running. Doug

This means your alternator charging system is NOT getting voltage to the chassis battery. ALL your boost switch does, is, combine BOTH the chassis and coach battery banks together while the switch is held. On Tiffins your year, there is a addon solenoid Tiffin installs that routes alternator current to the chassis battery. Also, in extreme cases, the RV owner has MISSED installing the extra Positive cable on the chassis battery for the Genset and charge. They have done this when replacing the battery or disconnecting the chassis battery cables. I have seen this more than a dozen times on Tiffin's where the owner will swear he has all cables connected and he comes in and I walk out and show him the pos cable NOT connected. 1. It is usually BLACK/ 2. Since it is black he connected to the negative. Doug

[larry_cad]

Verify that the breaker on the Genset is not tripped.

[wa8yxm]

beaubeau wrote:
Thanks!

As far as I know, there is no battery disconnect. I had one on a Bounder, as well as on a Born Free, but I don’t know of one on this RV.

Sorry that was a response that mentioned a disconnect.

There is also a circuit breaker or fuse on the house batteries... However I'm not sure it should affect the generator.. Sounds like batteries are very very low.

Isolator systems are designed to parallel house and chassis when the Chassis is charging (And in some cases when the house is charging) but some of them are voltage sensitive. they won't cross connect till the voltage gets high enough (primary (The side with charging) is sufficiently charged.. Not sure exactly what the trip point is.

THe Aux Start button overrides the isolator But I've heard my isolator clunk/clunk (on off) as the voltage changed when batteries were very very low. (Saw evidence that was what was happening in brightness of lights and such) Once it had cycled a few times it locked in and everythign charged.

[beaubeau]

Thank you

way2roll wrote:
Sounds like you have a parasitic draw on your chassis batts and it's killing them. In a previous MH that happened and wasn't enough juice for the disconnect solenoids to work. When going to sit for more than 2 weeks or so I used to disconnect the negative terminal.

[beaubeau]

Thanks!

As far as I know, there is no battery disconnect. I had one on a Bounder, as well as on a Born Free, but I don’t know of one on this RV.

wa8yxm wrote:
Ok, If you have a disconnect on the negative Battery post. and it was Disconnected.. Then I have no clue why the Aux Start got the coach started other than luck.. Sometimes a battery can "Wake up" on the first try though in the summer that's rare (more a winter thing).

How AUX-Start works.
Parallels house and chassis batteries so it's kind of like a built in jump start.
Why it won't work if you have a Disconnect on the House batteries.. Because they are disconnected.

Why it let the generator start: The With the AUX-START pressed the generator used the CHASSIS battery... Normally it starts off the house.

Why it died when you released.. No 12 volts no more. had you waited for the ATS to AT (The auto Transfer switch to auto transfer) Then the converter should.. in theory.. have held the Generator operational.

[beaubeau]

Super!
This makes sense, thank you. All except that the generator doesn’t run even if the chassis engine is running, unless AUX-START is held down.

dougrainer wrote:
2008 Tiffin. The chassis starts the Genset. It takes 12 volts continous for the Genset to run. Gensets do not supply 12 volt power once they are running. So, you got the Genset started with the Battery boost button. It takes the COACH batteries to engage the battery boost. So with the battery boost button pushed ON, your Genset started from the coach batteries and the coach batteries supplied the 12 volt power to keep the Genset running. Once you released the Battery boost, the Genset and Chassis side LOST the 12 volt signal. Hence the Genset died. Have you tried the same operation but start the Engine first and leave ON? Then boost to start the genset. The Engine alternator will supply the 12 volts required to keep the Genset running. Doug

[wa8yxm]

Ok, If you have a disconnect on the negative Battery post. and it was Disconnected.. Then I have no clue why the Aux Start got the coach started other than luck.. Sometimes a battery can "Wake up" on the first try though in the summer that's rare (more a winter thing).

How AUX-Start works.
Parallels house and chassis batteries so it's kind of like a built in jump start.
Why it won't work if you have a Disconnect on the House batteries.. Because they are disconnected.

Why it let the generator start: The With the AUX-START pressed the generator used the CHASSIS battery... Normally it starts off the house.

Why it died when you released.. No 12 volts no more. had you waited for the ATS to AT (The auto Transfer switch to auto transfer) Then the converter should.. in theory.. have held the Generator operational.

[dougrainer]

2008 Tiffin. The chassis starts the Genset. It takes 12 volts continous for the Genset to run. Gensets do not supply 12 volt power once they are running. So, you got the Genset started with the Battery boost button. It takes the COACH batteries to engage the battery boost. So with the battery boost button pushed ON, your Genset started from the coach batteries and the coach batteries supplied the 12 volt power to keep the Genset running. Once you released the Battery boost, the Genset and Chassis side LOST the 12 volt signal. Hence the Genset died. Have you tried the same operation but start the Engine first and leave ON? Then boost to start the genset. The Engine alternator will supply the 12 volts required to keep the Genset running. Doug

[CA_Traveler]

I have a disconnect switch on each negative battery post. Hence the only drain is battery self discharge.

[way2roll]

Sounds like you have a parasitic draw on your chassis batts and it's killing them. In a previous MH that happened and wasn't enough juice for the disconnect solenoids to work. When going to sit for more than 2 weeks or so I used to disconnect the negative terminal.

[enblethen]

Verify that the battery disconnects are connecting the batteries. Easy way is to cycle batteries off then back to on.