Underhood versus Onan

[markopolo]

Just a few general notes:

UG = auxiliary alternator plus inverter.
Regulator programming includes limiting the auxiliary alternator output to protect alternator.
Solar charging can be way more than a trickle charge. 10, 20, or 30 times more easily obtainable.
Deep cycle lead acid batteries are specifically designed for deep draw downs - eg: golf cart

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I wonder if it is necessary to limit input to the house batteries in GeorgeRa's setup if it is a stock alternator + chassis battery + 230AH house batteries.

I'd first determine how often a setup like that results in more than 40A at the house batteries and then determine the duration at more than 40A to see if any limiting is needed.

If limiting is needed then would the $$$ be better spent on an additional battery? (assuming battery bank longevity is the goal)

[booster]

Good points from Marko and definitions.

In GeorgeRa's application, because it is a factory alternator use installation, I do think it needs to be limited, as much to protect the alternator as the batteries.

If his AGMs are like ours in acceptance rate, they will likely accept 100 amps or more for quite a while, if it is available, which would be a bit much for the batteries if they can handle the .4C ours can, or 92 amps in GeorgeRa's case, but would also likley get the alternator quite hot, when another 20-30 amps are added to run the van chassis, plus whatever other power is being used in the coach like frigs (especially propane ones) or charging up stuff.

The big difference, IMO, when you charge off the van alternator is that you lose the good stuff that the underhood generator system provides. This is mostly not the alternator and it's capacity, but the control from the regulator. It gives overtemp protection for the alternator and the batteries, plus a multistep charge profile, so you aren't hitting your batteries with many hours of full charge voltage on long drives if you leave full, or almost full. You lose all of those things if you use the van alternator without a DC to DC charger in the line, although you can get the battery overcharge protection back with a disconnecting style separator that you can control yourself.

The only other way I can think of to limit the current would be to put an adjustable field control on the alternator so you could turn it down when needed, but then you lose voltage also in most cases. If there is a good way to turn down just the amps, for lower cost that the DC-DC charger, you could do that and get most of the benefit by doing that and having a disconnect.

I am certainly not against charging off the van alternator, as I think the probably well over 90% of users would be just fine with that setup for up to 200-250ah of batteries. The continuing change to AGM from wet cells has changed the dynamics of it a bit, I think, as the AGMs will accept enough amps to heat up themselves and alternator, where wet cells would take considerably less amps.

Personally, if I had the choice, I would use a DC-DC charger even for a engine generator setup. That way you could use an internally regulated alternator, no external regulator, and be able to match the output to what batteries you have by the size of the DC-DC charger. I would have built our system that way, if I could have found a DC-DC charger large enough for what we need, I think. We achieved a bit better charge control with our system, but it is a manual control, and most folks want/need it to take care of itself.

[avanti]

Just remember that modern vehicles have highly-engineered intelligent charging systems intended to save fuel and improve performance. Generally speaking, taking large amounts of power from them will produce unpredictable results. Mercedes forbids upfitters from taking more than a small amount of power from the engine charging system. DIY folks often get away with ignoring these specs, but I do not think it is a good idea, and probably will become even less so in the future.

One of the reasons I got a second engine alternator was because I was getting disappointing charging performance from my 2014 Sprinter chassis alternator. I must say that I feel better about taking these issues out of the equation.

[booster]

Agree with Avanti, especially on Sprinters.

Have they come out with limitation numbers for the Promasters and Transits? I don't recall ever seeing any.

[BBQ]

.

Maybe the 48v alternator/generator is the solution?

[GeorgeRa]

Thank you all for the helpful discussion.

My van is 2013 Sprinter. The MB cut-off relay, the one between the auxiliary battery and the alternator, and 2 AWG wiring can support up to 100A. The 2 AGM Fullriver batteries should take at the bulk stage from 0.15-0.35 X C20 = 35A - 80A charge at 77°F, less at higher temperatures. http://resources.fullriverbattery.co.../batteries.pdf

With battery deeply discharged charging current exceeds the 80A maximum, and in several minutes, it drops down. I have no control of charge rate with higher battery temperatures, with hot battery the overcharging could be happening keeping me completely unaware.

It works fine now but I would like to have some limits on the charging current for my peace of mind. The 40A limit I picked is arbitrary, if it is a simple current cut-off it should be OK, with DC to DC charger the limit could be higher, 50-60A or even 80A.

Awhile back I purchased a Magnum ME-SBC battery disconnect which has 25A limit, my plan was to insert it between the cut-off relay and house batteries to prevent overcharging the starting battery. But 25A max is too limiting. Smart Battery Combiner | Magnum Dimensions. This unit could be set for connect/disconnect/reconnect different voltages, I think it was a premature purchase.

2013 Sprinter can provide higher alternator current than 2014 and up so no issue up to 100A.

Battery to battery charger is certainly best option to provide correct charging profile. Sterling is an option and it is popular, Kisae 30/50A B>B chargers DMT-1250 - Kisae Technology is another option.

One of the potential option would be to use an adjustable current sensing relay to override the MB cut-off relay. So, for these few times when current is too high the MB relay would be triggered off until reset, but, there would be no alternator charging until batteries will get charged enough by solar or AC charger. AS1 Current Sensing Relay | NK Technologies

I need to make up my mind, which way to go. Doing over again I would pick a dual power source charger to take my 300W PV and the alternator inputs. One of the scenario is doing nothing, as it was stated, I need to figure out how often the alternator exceed the charging current and if rarely doing nothing could be my best choice. Spending $400-500 of the DC>DC charge controller to extend batteries' life perhaps is not justifiable.

[Saldar]

Originally Posted by booster

https://www.amazon.com/Sterling-ProC...F6F574XDJGBYDS

Sterling ProCharge-B Battery to Battery Charger | 12 Volts In - 12 Volts 50 Amps Out

Would a Sterling B2B like this also stop alternator charging when the house battery reaches full?

[booster]

Originally Posted by Saldar

Would a Sterling B2B like this also stop alternator charging when the house battery reaches full?

It is a full feature smart charger, so within the limits of it's algorithm, it will take the batteries to float when they are full, just like a shore or solar charger. That is a very big benefit IMO.

[GeorgeRa]

Thinking out loud .

How about getting a solar charge controller which is a DC to DC device instead of a pricey Sterling or Kisae. For example, this 40A MPPT Solar Charge Controller Tracer 4210A. I sent these folks an email with this question. I could be wrong, but a DC to DC is a DC to DC chage controller. The MPPT is useless in this case. The source resistance is different, but this shouldn’t make much difference.

https://www.aliexpress.com/item/40A-...StoreLevelAB=2
Based on my recent positive experince form the purchase of the headset radio from Aliexpress I am willing to experiment.

This is another one by Xantrex C Series PWM Charge Controller for $200 https://www.solarpanelstore.com/sola...ntrex_c60.html

Or, disconnect the cut-off relay on connect alternator positive to my Morningstar MPPT 45 solar controller input with solar panels being disconnected if it would be necessary.

What am I missing?

[avanti]

Originally Posted by GeorgeRa

Thinking out loud .

How about getting a solar charge controller which is a DC to DC device instead of a pricey Sterling or Kisae. For example, this 40A MPPT Solar Charge Controller Tracer 4210A. I sent these folks an email with this question. I could be wrong, but a DC to DC is a DC to DC chage controller. The MPPT is useless in this case. The source resistance is different, but this shouldn’t make much difference.

https://www.aliexpress.com/item/40A-...StoreLevelAB=2
Based on my recent positive experince form the purchase of the headset radio from Aliexpress I am willing to experiment.

This is another one by Xantrex C Series PWM Charge Controller for $200 https://www.solarpanelstore.com/sola...ntrex_c60.html

Or, disconnect the cut-off relay on connect alternator positive to my Morningstar MPPT 45 solar controller input with solar panels being disconnected if it would be necessary.

What am I missing?

I asked this question over at Sprinter Source a few years ago (you participated in the thread). Graphite Dave responded as follows:

A few years ago I called Morningstar with the same question. They said no. No way to control the amount of amps from alternator with a low house battery.

If this is accurate and I understand him correctly, I guess they are saying that the design of the solar controllers are dependent on the assumption of limited current availability from the solar panels.

[booster]

The might also have trouble with the ripple that you get off and alternator, as they are used to pretty clean DC.

[GeorgeRa]

Originally Posted by avanti

I asked this question over at Sprinter Source a few years ago (you participated in the thread). Graphite Dave responded as follows:

If this is accurate and I understand him correctly, I guess they are saying that the design of the solar controllers are dependent on the assumption of limited current availability from the solar panels.

I didn’t to remember that particular thread, good catch. I remember ongoing discussion of using an inverter to power an inverter/CHARGER combo. I searched for it noticed that you started that thread, this was mid-2015.

“This may be a dumb question, but...Is there any reason one couldn't use a good solar controller as a DC-DC battery charger for charging the house battery from the engine alternator? They are quite a bit cheaper than devices designed for this application. Aren't they basically the same thing?”

I believe that Dave has the Mornigstar MPPT 15A so perhaps he was calling about his unit. If you look at CTEK 250S with CTEK SmarPass combination or KISAE both of them have this dual input option.

It could be best option for me to use the Morningstar MPPT 45 if possible, one wire. I agree, if the current can’t be throttled down it would not be possible. I am going to email Morningstar that question.

[cruising7388]

Originally Posted by avanti

Mercedes forbids upfitters from taking more than a small amount of power from the engine charging system.

Where can I get more details regarding this limitation by Mercedes?

[Davydd]

Originally Posted by cruising7388

Where can I get more details regarding this limitation by Mercedes?

The Daimler Vans Upfitter Portal here...

https://www.upfitterportal.com/en-us/

You can download the Body and Equipment Guidelines.

[GeorgeRa]

Originally Posted by GeorgeRa

I didn’t to remember that particular thread, good catch. I remember ongoing discussion of using an inverter to power an inverter/CHARGER combo. I searched for it noticed that you started that thread, this was mid-2015.

“This may be a dumb question, but...Is there any reason one couldn't use a good solar controller as a DC-DC battery charger for charging the house battery from the engine alternator? They are quite a bit cheaper than devices designed for this application. Aren't they basically the same thing?”

I believe that Dave has the Mornigstar MPPT 15A so perhaps he was calling about his unit. If you look at CTEK 250S with CTEK SmarPass combination or KISAE both of them have this dual input option.

It could be best option for me to use the Morningstar MPPT 45 if possible, one wire. I agree, if the current can’t be throttled down it would not be possible. I am going to email Morningstar that question.

Answer from Morningstar regarding their TS-MPPT-45: No. What you would need is a dedicated Alternator Charger. – clear answer, Dave was correct.

Answer from Aliexpress regarding https://www.aliexpress.com/item/40A-...cf829c511e215: Dear friend, the charging way is ok, but you should add some voltage control setting, because MPPT controller range may not perfect for the battery as dc souce. – I am not sure what this means.

I think combining PV with alternator charge controller could be the trend and CTEC and KISAE are the first ones. Back to search.

[cruising7388]

Originally Posted by Davydd

The Daimler Vans Upfitter Portal here...

https://www.upfitterportal.com/en-us/

You can download the Body and Equipment Guidelines.

Thanks. I see that MB specifies a 40 amp limitation but it isn't clear whether their Canbus program effects this limitation or whether it's just an instruction to the upfitters.

[avanti]

Originally Posted by cruising7388

Thanks. I see that MB specifies a 40 amp limitation but it isn't clear whether their Canbus program effects this limitation or whether it's just an instruction to the upfitters.

Nothing enforces it (except perhaps the MB bureaucracy to the upfitters). It is an engineering spec. Violate it at your peril. Note that Sprinters have had LINbus-controlled alternators for many years. As a practical matter, the spec isn't that important (within reason) pre MY2014, and it is commonly ignored by DIY upfitters without apparent consequence. However, as of 2014, the I-4 engine (like many modern vehicles) comes with Intelligent Battery Management (option code E33), which involves current sensors directly on the battery terminals, special algorithms in the ECU that manage the battery charge rate and alternator output in order to maximize performance and fuel economy by doing a kind of regenerative braking--things like turning down the alternator during acceleration, and saving some "space" in the battery for long downhill runs.

In such systems, the specs start to matter more. For this reason, direct high-current connections to the vehicle charging system are becoming increasingly dicey.

[Davydd]

Originally Posted by cruising7388

Thanks. I see that MB specifies a 40 amp limitation but it isn't clear whether their Canbus program effects this limitation or whether it's just an instruction to the upfitters.

I took it the alternator had to satisfy the engine and chassis needs first and the 40 amp limitation was a safe allowance left over. For years Pleasure-way and Great West Van would not install more than one house battery in keeping faith to the guidelines. Even when I bought my Great West Van in 2011 they were very reluctant to add a second house battery. It has only been these past few years that upfitters had dare to challenge guidelines. Now, every one is going to big battery banks and the second alternator is really the only practical solution and if the independent boondocking trend continues it will be the demise of the Onan generator in Class Bs, IMO.

I cannot emphasize the Onan is just a substitute for shore power when you have low battery capacity. A second alternator is for charging while driving with high battery capacity that the primary alternator is not sufficient enough to charge. With the high capacity battery then you bridge your stay. Idling is only a back up, emergency, or unanticipated change of plans. Knowing your systems you probably never idle other than testing it or demonstrating it for friends.

[mlts22]

My two centavos:

Why not both? I'm still sidelined due to 2016 being a brutal year financially, but one of the things I have charted out is having a whole-house inverter like a MSH3012M that everything is hooked into. Then, have the secondary alternator feed the batteries, and the onboard 2800 watt Onan generator feed the inverter, so the engine can keep things powered, or both... the inverter can figure everything out. Of course, an automatic transfer switch is needed so the rig can figure out what to do if on shore power.

The advantage of this setup is the fact that you can either/or/both. For example, when I'm at a friend's cabin (which runs everything on a 20A circuit including a small A/C), the van's generator could easily pull power for hours on end, and not add wear/tear to the engine. When on the road or Wallydocking in a Texas summer, having power come from the relatively quiet engine doesn't hurt.

I know this is an oddball setup, but should do what I want nicely. It provides power to a remote cabin, where I wouldn't want to leave a generator around (for worry that someone skulking around when nobody is there might claim it as a prize, as the cabin is unmanned for most of the year.) With a vehicle's fuel tank, the generator can easily run a long time, which is important for 100+ degree weather.

[avanti]

Originally Posted by mlts22

My two centavos:

Why not both?

What you describe is exactly the setup I have. Van came with a genset, two batteries, and a large inverter. I added two more batteries and then a second alternator. The genset is still there. The only trouble is that we never use it. Too noisy, and for our travel style it is simply unnecessary. I have had the same tank full of propane for 2 years now.

I really should yank it out and have a place for a spare tire. But, it does serve as a backup "just in case". Eventually, I will probably get around to my under-body split A/C project, in which case I will probably need the space.