Voltage Concern

[Jon Wehrenberg]

Tony, Lets back up a little and start from the beginning. Your single alternator, dual inverter coach has an engine driven alternator. When no 120 volt input to the inverters is available (shore or generator power) the alternator driven by the engine provides the charging current. I believe yours has an external voltage regulator and that is what is determining the voltage to your batteries. It will generally be around 28 volts.

When the bus engine is not running, but has shore or generator power to the coach, the inverters become battery chargers. They can have voltages around 27.7 to 28.4. The range is because they can be set to charge gel cell batteries (lower voltage) or AGM batteries (higher voltage). See the link to charging below.

If your coach has been set for gel cell batteries I would guess you would see the lower voltages, but not as low as you describe.

Since you have three independent charging sources, the alternator, and the two inverters I surmise based on your readings all are working.

I can guess with confidence the alternator is working. The fact that the voltage goes up tells me that. It may be the inverters are in the float portion of the charging cycle which drops down to 13 to 13.2 (26 to 26.4) It is also possible you are set up to charge gel cell batteries.

This link will explain the charging voltages:

http://www.windsun.com/Batteries/Bat...ery%20Charging

[Jon Wehrenberg]

Thinking further about this I want to be sure that with the engine off, you also have the chassis battery charger turned off.

Here are my voltages, under the conditions shown, taken with a digital multi-tester at the locations specified

Chassis voltage reading location: RH post, chassis battery positive, and ground at the battery hold down bracket.

House voltage reading taken at the house battery equalizer 24 volt post and ground. The equalizer is on the forward bulkhead of the house battery compartment.

Chassis: Engine off.....25.5 volts (after engine has been off for at least one hour)
Chassis: Engine running.....28 volts

Note: it does not matter if the bus is connected to shore power or not because the inverters DO NOT charge the chassis batteries. The chassis battery charger is "off".

House: Engine running.....28 volts

House: Engine off, connected to shore power....27.75 volts. Note: the house battery voltage is dependent upon how the inverter is set up via the dip switches at the rear, and at what point in the charging cycle the voltage measurements are taken. It also matters what loads are on the house DC circuit. The tivoli lights are a heavy load and the voltage will be down a little.

None of this is actually as confusing as it sounds. As long as the voltages of the batteries go up when the engine is running, or are maintained when connected to shore power (house) everything is working correctly.

If you want to measure the alternator output, check the voltage at the center post on the blue isolator with the engine "off". It should read zero. With the engine running it should read 28 volts or thereabouts. If it does the alternator is working.

[merle&louise]

Tony,

Are you using a digital multitester? If you are using an analog multitester maybe it is just out of adjustment.

If you select ohms the needle should line up with the zero or end of the scale not be short or over the end of the scale. There is an adjustment (use a blade screwdriver) and you can adjust it to read exactly on zero.

Another way to test it would be to check the voltage readings inside your house and see if it reads exactly 120v AC.

[aggies09]

The multitester that I am using is a fairly new one and is digital. I am going to take Jon's approach (locations and conditions) and see where I am.

[Jon Wehrenberg]

Tony,

If you want we can literally walk through this on our respective coaches while communicating via an open cell phone line. We just need to nail down a specific time.

I strongly suspect everything is OK with your bus, but I understand the comfort in confirming that.

[aggies09]

Jon, I sincerely appreciate the offer. I haven't had time today to even go out to the bus barn and am getting prepared for the last presidential debate (gasp). Let me take some readings tomorrow and if I am still uncomfortable I will gladly take you up on your offer and try to schedule a time for a walk through.

Thanks for your assistance.