Basic alternator and 12VDC question

[trevor]

What would be the expected maximum alternator output (amps) if a coach is started with very low batteries (it was being "serviced" and took 3 months - and they did not have shore power all of the time!)?

Followup question - if the alternator is putting out an amperage that is higher than the 12VDC components are rated for, does the alternator amperage get sinked (drawn) by the batteries or does it flow through to the 12VDC system.

The coach system (not chassis) has 24V and 12V batteries (Vanner equalizers)

Thanks in advance

[Kenneth Brewer]

What would be the expected maximum alternator output (amps) if a coach is started with very low batteries (it was being "serviced" and took 3 months - and they did not have shore power all of the time!)?

Followup question - if the alternator is putting out an amperage that is higher than the 12VDC components are rated for, does the alternator amperage get sinked (drawn) by the batteries or does it flow through to the 12VDC system.

The coach system (not chassis) has 24V and 12V batteries (Vanner equalizers)

Thanks in advance

What would be the expected maximum alternator output (amps) if a coach is started with very low batteries (it was being "serviced" and took 3 months - and they did not have shore power all of the time!)?

Followup question - if the alternator is putting out an amperage that is higher than the 12VDC components are rated for, does the alternator amperage get sinked (drawn) by the batteries or does it flow through to the 12VDC system.

The coach system (not chassis) has 24V and 12V batteries (Vanner equalizers)

Thanks in advance

The follow up question's answer: The 12vdc components draw no more amps unless the supply voltage goes up or, in specific (unlikely) cases, there is a dead short to ground. That shouldn't happen (drawing more amps) unless the voltage regulator on the alternator has failed. Even if that should happen, the coach batters should be protected by the equalizers which should shut down at 31 volts or so. If you have a 24V alternator, the equalizers (properly operating) ensure the batteries get 12V each. The 12V loads should, in any case, be protected by fuses and/or breakers. The amperage the alternator produces is the rated output of the alternator at its rated voltage. The current is divided among the loads. E = I x R. The amperage cannot be higher than the component(s) would draw if the voltage, E, is fixed as well as the load resistance or impedance. If you had only one light bulb connected to the source - only that amount of amperage would be drawn. Otherwise you could not turn breakers off without frying the rest of the loads.

The alternator's current output is adjusted by the voltage presented on the load it sees, up to its capactiy. If the regulator is satisfied the voltage it sees hasn't dropped, it is happy. If the voltage drops at the load, the field (internally) is adjusted to increase amperage (to its limits). E=IR. If the voltage climbs to undesired levels (29-31V) current output is dropped (E=IR).

We have the 270 alternator. I have seen approximately 150 - 160 amps being drawn according the gauge when both the coach and chassis batteries batteries were low (the inverter/chargers quit when the voltage has dropped to 10.5 according the manual and my less than perfect memory. However, I am not exactly sure whether the measurement is indeed being taken on the output of the alternator, or elsewhere. The others will weight in on this with their experiences.

[Jon Wehrenberg]

I often ponder (a southern term) in amazement how my converter has set up the coach electrical system so nothing bad happens when a combination of events occur simultaneously. For example. we can be running our bus engine which means the alternator is charging the batteries and supplying power to all the DC systems.

At the same time we can be running our generator (such as when running appliances) which in turn makes our inverters turn into battery chargers, and there is no ill effects on our electrical system as the result of two separate power sources applying power to the bateries or house systems.

My conclusion based on what I have noted is that our electrical suppliers (alternator, generator, inverters) all have regulated power. Our alternators have voltage regulators so we do not exceed certain voltages. Ditto with our inverters. The point is as the batteries are recharged the voltage is regulated which in impacts the current.

The limiting devices are the voltage regulators, but we also have circuit breakers. And if they fail we have monitors to alert us to conditions which exceed certain limits, such as our Vanner monitors.

Where we ARE NOT assured of protection is in the battery charging if we use batteries that are of a different type from those originally supplier with the coach. Each type of battery has a charging protocol which must be used and the failure to use those limits will result in the shortening of battery life or in the worst case a total battery failure. An AGM battery cannot be charged using the same voltage levels as a Gel or flooded cell battery. This is where the owner must make certain the voltage limitations are observed.