Voltage Concern

[aggies09]

I have a question relative to voltage for the engine and for the house. I have two gauges on my dash each labeled engine and house. The engine voltage appears to read about what I think it should, somewhere between 26 and 27 volts. However, my house gauge displays a pegged out gauge of somewhere north of 28. What should these guages read? Once I have determined that, I need some input on what might be causing such a high reading on the house side and what do I do to diagnose/repair. Thanks for your thoughts.

[Jon Wehrenberg]

Tony,

With the engine running and the shore power and generator "off" the two should read almost the same. Look real close because they are 2 volt spacings and you should see them both around 28.2 to 28.4. That is about normal.

With the engine "off" and hooked to shore power or the generator running the engine gauge voltage should be at zero, but the house should be at 28.2 to 28.4.

This is a good opportunity to get a multi-tester and check both sets of batteries (right at the chassis battery post and ground, and easiest if you check it on the house batteries at the equalizer next to the house batteries).

Check voltages with the engine running, the engine off, and the inverters on and off. I would not recommend running the chassis battery charger all the time.

The chassis batteries with the engine off and the surface charge dissipated should read 25.4 to 25.6. Ditto for the house.

[phorner]

Looks to me like your chassis (engine) battery voltage is OK. However, your house battery voltage should be in the vicinity of 14 volts if charging/fully charged.

I would check the actual voltage with a multi-meter to be sure.

Are you seeing this voltage with the engine running?

Or, are you seeing this while plugged in and the chargers working?

I was experiencing high charging voltage when the engine was running and ended up with a new alternator. You can also check the voltage at the cigarette lighter on the dash to compare with your gauges.

This is based on my coach which is a 12 volt system. Your Elegant Lady may be 24 volt?

[Jon Wehrenberg]

Tony has a 24 volt coach. To anyone reading this the information is valid no matter who the converter is and if the coach is a 12 volt coach divide the values by 2.

Also if you want to get into a little more detail refer to the Prevost Electrical Systems article under information sharing on the POG home page.

[Kenneth Brewer]

"I was experiencing high charging voltage when the engine was running and ended up with a new alternator. You can also check the voltage at the cigarette lighter on the dash to compare with your gauges."

It is possible this might be fixed without the cost of a new or rebuilt alternator, or voltage regulator and ballast resistor (around $180 or so), for less than $10, if the brush is severely worn and/or stuck in its bore (due to the wear of the brush), a Leece-Neville alternator brush replacement costs around $2, but also a need for expansion of your curse word vocabulary when engaging in the installation.

I originally thought the voltage regulator had a fault but after its removal found the problem to be the brush assembly which contacts the voltage regulator directly (spring loaded). If the brush doesn't make contact with the rotor shaft, or with the regulator at the other end, voltage output goes high. I have the procedure I used if anyone is interested. Another accompanying symptom can be the pulsing nature of the voltage output with the lope of engine rpm at idle. In my case on the Bluebird (12 volt system) it caused problems with rear view camera image.

[aggies09]

The coach is a 24 volt system, and the numbers I posted were with the engine running. If I am understanding the responses thus far, it appears that what I am reading on the gauges is close enough to be tolerated. If i am interpreting this incorrectly, please follow up. thanks.

[Jon Wehrenberg]

Tony,

Just to make sure there is no issue, you used the term "pegged out gauge", and "north of 28". Those are scary words.

If I am correct you have a single alternator coach. The large alternator output goes through an isolator to the house and chassis batteries. With the exception of a change in value because of varying loads, when the engine is running both sets should be at 28.4 volts (give or take a tenth or two).

When the engine is not running and you do not have the generator or shore power applied to the coach the resting voltages should drop back to 25.4 to 25.6 or thereabouts.

If you are in those ranges your voltage values are correct.

[aggies09]

Jon, both are not within a tenth of that 28.4 while running, so I will start taking some readings and post back with results. Thanks.

[Jon Wehrenberg]

I may have shot from the lip.

My house reads a slightly different value on the dash gauges. It could be gauge error, or a slight variation in the actual battery voltage. When I use my multi-tester to check voltages they are both very close so I attribute my different readings to how the gauges are calibrated.

When you check yours you may find the same thing.

I think my coach voltage shows about .5 volts lower than the house, but with the tester they are almost exactly the same. The values you get from the multitester are likely to be more accurate.

[aggies09]

Using the multitester I get the following readings:

House:
26 volts with engine off plugged into shore power
26.5 volts with engine running

Engine;
26.2 volts w/engine off plugged into shore power
27.1 volts w/engine running

These readings are obviously not the 28.2 +/- that I believed I was supposed to be getting.:confused: Does this mean that I have an alternator issue?

[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/Battery_FAQ.htm#Battery%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.