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Old 02-08-2019, 11:21 PM   #15
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We had the exact same problem before we switched to Lifeline batteries about 18-mos ago. After all the investigation into the alternator, BIM, battery testers and multiple discussions with CS, I set AUTOGEN on during long drives (set at 12volts), and never had another problem. Mike O'Connel advised I do that until I ditched the horrible Discover batteries supplied by Entegra. We never had this problem after switching to Lifeline. Easy fix!
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Old 02-09-2019, 06:00 AM   #16
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Jim, good advise suspecting the Discoveries. Been there with mine. Mine didn't make it 2 years from being mistreated at the factory before delivery.

Doing a 4 hour draw test and seeing what the charge is at the end of 4 hours is probably the best first move. That bypasses all the switches, relay, etc. starting with fully charged batteries.
I should do that while the coach is new so I have a reference point as the batteries start to age. Good idea, thanks Jim.
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Old 02-09-2019, 11:42 AM   #17
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The laws of physics vs personal beliefs

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Originally Posted by twinboat View Post
Most if what you say isn't the case.

For one point, and an important one, the cables between the battery banks are the same size. The BIM is also used as the boost switch and needs to carry starting current.

There are other points, but others are pointing them out.
The laws of physics apply regardless of personal beliefs. My personal beliefs also suffer from this human condition.

I laid out the scenarios as best I could. I explained the physics as best I could. Your general dismissal of all of it is useless because it does not allow me to adjust my explanations to clarify.

I do not have experience with the specific wiring and the BMI device the OP has. Certainly others have much better understanding of those issues.
On the other hand, I do have excellent knowledge about electricity, electrical systems, electronics, and lead/acid battery charging physics. As I stated in my post, with the correct equipment you can do anything.
Does the electrical system in the OP unit provide two separate charging circuits each with it's own voltage profile? If not, then the physics I explained apply.
If you have alternate theories, please explain and I will address them. If you have specific questions about my explanations please ask them.
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Old 02-09-2019, 12:26 PM   #18
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Does the electrical system in the OP unit provide two separate charging circuits each with it's own voltage profile? If not, then the physics I explained apply.
The OP's coach contains at least two separate charging systems- the vehicle alternator(s) and the inverter/charger. There may be more (solar, for instance). There are at least three charging "circuits" for these two systems- alternator, inverter/charger and the cross-charging between the battery banks.

Here's an explanation of the cross-connect circuit. In a motorhome like the OP's (as opposed to a travel trailer), the chassis battery bank and the house battery bank connect to the posts on a high-current (e.g., 200A) solenoid. Both cables are large gauge- often the same size as the starter cable. The solenoid activation signal comes from a voltage-sensing circuit, often with its leads attached to the same posts as the battery cables. When that circuit senses a charging voltage on one post (that is, battery bank), it compares that with the voltage on the other post. If there is a significant difference, it activates the solenoid. This electrically connects the two battery banks together. At that point, the charging current flows to all the batteries in the bank.

That, in a nutshell, is how the cross-charging circuit works.

Under normal circumstances, when underway the alternator produces charging current and the charger function of the inverter is disengaged. The inverter may be producing 120VAC, thus draining the house battery bank, but that just has the effect of lowering the bank's voltage (over time). [Note: Other posts correctly point out that if power is being drawn out of the house batteries while going down the road it is possible to end up with a less-than-hoped-for voltage level on the house batteries at the end of the trip.] So, under normal circumstances, there is only one charging source at a time.

Thanks for giving me the chance to clarify the replies I and "twinboat" have given the OP.
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Old 02-09-2019, 01:27 PM   #19
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Automotive battery charging
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In general, I disagree. In this specific case, any number of things could be going on.

The reason I disagree is because motorhomes have been built with chassis-to-house charging systems for many years. If they didn't work as designed most of the time, we'd be driven crazy. The technology has changed, from diode isolators to solenoids (often, but not always) under the control of voltage-sensing circuits, but the principle has remained the same: The chassis and house batteries are connected together as if they were one bank, and charged by the alternator(s). Sometimes the same equipment is used to charge the chassis batteries from the house battery charging source(s). Ö


Thank you for a good critique. I agree with the driven crazy part. Here is my answer.

"diode isolators to solenoids (often, but not always) under the control of voltage-sensing circuits,:

Diode isolators and solenoids are switching devices. They can connect and disconnect. The voltage-sensing circuits are usually simple detection of voltage presence and cause switching to available power sources. It is possible voltage sensing could go further and pick a source with the best voltage available. There are other possibilities, but I am not aware of any in earthbound vehicles.

The usual plan is to connect or disconnect the house batteries to the engine charging system. The chassis battery remains connected to the vehicle charging system at all times. The engine charging system must maintain the chassis battery and provide electrical power to the vehicle systems. It is not free to optimize charging to the house batteries. The switching device can connect or disconnect the house batteries based on the house battery charge level, but it can only get what the vehicle system is currently providing.

So what is available from a vehicle electrical power system (usually an alternator). I have never been involved in designing a vehicle power system, but I know there are many alterative designs. Whatever method is chosen, it must meet the life testing requirements of the entire vehicle as well as the life of the specific type of chassis battery chosen.

Different battery designs have different charging profile requirements. One deep draw battery may be optimized by charging fast assuming you will start an auxiliary generator and run for a short time, charge it fast, and shut it down. Another may optimize by charging slow for a long period like using solar panels.

Automotive batteries are optimized for extremely high current draw, followed by quick recharging. They do not need to be charged to 100% every time you start and run your car. Urban driving may never get the charge level much above 70%. Likewise, it is unlikely to get below 30% if everything is working properly.

Automotive charging systems are optimized for this profile. The profiles are especially sensitive to deep discharge because that destroys the cold cranking capacity. The charge systems all are sensitive to overcharging because that boils the electrolyte, increase maintenance cost, and decreases battery life. Acid expelled damages adjacent equipment.

This profile means the designer had to choose how to prevent overcharge. The usual way is to monitor current and voltage out of the alternator. He must anticipate how much current vehicle systems consume and estimate how much is flowing into the battery alone. He then chooses a cutoff point and causes the alternator voltage to drop to avoid overcharging. So the voltage usually is between 14 and 15 volts immediately after starting, but will be lower later. Maybe 13.6 volts.

To charge the house batteries you must do something similar, but the point at which you drop the voltage may be hours later. Add in house appliances running and house batteries being charged and you have made the problem worse. If there were little to no line resistance to the house side, you would probably get overcharging of the chassis battery. The vehicle system would see high current draw and assume it needed to fast charge the chassis battery when it actually did not. 12 volt battery charging is more sensitive to line resistance than almost any other 12 volt use. There are well established formulas to model this. Unfortunately I have long ago forgotten them.
Motor home builders may or may not buy different chassis units with different profiles programmed into the chassis charging systems. House current consumption and house battery charging makes the task of choosing a charge profile much more unpredictable. Results are likely to be less optimal. Certainly, more exotic monitoring systems are possible. NASAís are out of this world.

The OPís problem is either something is not working correctly or the house side power consumption is higher than the vehicle system is providing (as other have suggested). Certainly good troubleshooting procedures are in order. Measuring current and voltage at various points in the system will greatly help to isolate the problem. Shortcuts such as turning heating devices and other appliances off and retesting often produce good results.
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Old 02-09-2019, 02:22 PM   #20
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When the voltage sensing device, used on MHs with large house banks, ties the banks together the high CCA chassis battery will send its energy to the discharged, lower voltage, deep cycle battery. Voltage travels from high to low.

That causes the high CCA battery's voltage to drop. The alternator/regulator, connected to the chassis battery senses that drop in voltage and increases its amp output, to raise its voltage.

The voltage sensing controls have failsafe routines that disconnect the banks if the chassis battery voltage drops below what the chassis needs to run.
That comes into play with deeply discharged house banks or high amp devices drawing them down.

The control will reconnect again when the chassis battery recovers, and again attempt to maintain chassis voltage while connected.
Over time the house bank will recover enough so that the control will stay connected without over taxing the charging system.

In smaller MH, the chassis and house batteries are about the same size and are simply connected when the key is switched on. The chassis charging system can handle the combined banks without overheating.

Diode isolators fell out of favor because only the chassis battery controlled the alternator regulator. Once the chassis battery recovered, from the startup, it cut back the output. That caused a slow recharge of the house batteries.
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Old 02-09-2019, 03:10 PM   #21
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Probably more than I needed to know. Wish we could stick to Entegras.
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Old 02-09-2019, 03:36 PM   #22
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Quote:
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Probably more than I needed to know. Wish we could stick to Entegras.
X2, simple problem should have simple explanations that everyone can understand.
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Old 02-10-2019, 05:13 PM   #23
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Quote:
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Probably more than I needed to know. Wish we could stick to Entegras.
I pretty much stopped reading when the chest thumping started


Not sure how the OP determined his house voltage was down, but ..

On my previous Monaco I installed a pair of Laskar EMV1200 voltmeters in the dash. Chassis and house power are easily found behind the center dash, the meters install with a 1/4" hole, easy peasy

These are on my list for our aspire.
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