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Discussion Starter · #1 ·
Planning my electrical and will likely have 2, 100 amp-hour, LiFePO4 for my house batteries that will be charged via a B to B charger (current candidates are a Kisae or Renogy 50 amp charger, or a Sterling 60 amp charger). I have the 2 starter battery setup with the heavy duty 230 amp alternator. We likely plan to be driving often, so at this point, I am not planning on having solar. In case we decide to extend our stay at a particular location and start to run low on juice, will running the vehicle at idle rpm's be sufficient to charge the house batteries? Also, any positive or negative comments on B to B chargers are welcome. Thanks!
 

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A old thread but not that old.

 

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The amount of current you draw while at your extended stay will have a large impact on how long your batteries last, ie. what appliances/electronics are you planning to use while parked.... You have a voltage meter on the batteries to keep an eye on them while parked? Idling the motor will certainly charge the batteries but it's not going to be fast charge. I think a combination of that and solar is a good idea.
 

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Thanks Michael, reading through that 11 pages just ate up two hours of my morning. Not only did it not provide a simple answer suitable for ME, but it also did an excellent job of reinforcing what ranxerox once said about my ineptitude. I've definitely got a lot of that.:p

Maybe I can just use a hand crank or stationary bicycle to charge my batteries.
 

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Planning my electrical and will likely have 2, 100 amp-hour, LiFePO4 for my house batteries that will be charged via a B to B charger (current candidates are a Kisae or Renogy 50 amp charger, or a Sterling 60 amp charger). I have the 2 starter battery setup with the heavy duty 230 amp alternator. We likely plan to be driving often, so at this point, I am not planning on having solar. In case we decide to extend our stay at a particular location and start to run low on juice, will running the vehicle at idle rpm's be sufficient to charge the house batteries? Also, any positive or negative comments on B to B chargers are welcome. Thanks!
It is impossible for anyone to answer your questions without knowing your electrical loads. The first step is ALWAYS to do a load analysis.

The purpose of a load analysis is to determine how much electrical energy you will need each day. It is impossible to intelligently design an electrical system without knowing what your loads are. This Page has a good explanation on how to do a proper load analysis.

Do a load analysis. Post it here. That's what we need to give you good and specific advice. I'll say it one more time. Everything flows from the results of the load analysis.
 

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Short answer is yes they will charge

the longer answer Is what people are trying to say above. How much power do you need. If a lot you might be idling 24 hrs a day to keep up. you nwe’d to figure that out. No one can tell you that
 

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Without reading the linked thread I think the original post would like a definitive answer to the question of output of the generator at idle. I remember a lot of graphs from that thread, last time I read it, and it’s hard to interpolate off the far end of the graph as it approached zero.
I’m less than ignorant about the electric goings on in a vehicle but has anyone actually measured the output at idle? How would you do it?
Imagine with my lack of knowledge and understanding I am going to attempt to put in a house system when I get my van. Since I live in Seattle I assume I will have many marine electricians to choose from if/when I need a bailout.
 

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...cut... but has anyone actually measured the output at idle? How would you do it?
Can't remember where I read it, but IIRC someone put a ammeter with a hall effect sensor on the alternator wire to get an idea of what was going to his batteries under different electrical load configurations.
 

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Without reading the linked thread I think the original post would like a definitive answer to the question of output of the generator at idle.
Alternator output charts can be found in Section 4 of the BEMM. It appears that output at idle is far above the 50 or 60 amps necessary to max out the proposed B2B chargers.
 

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I have the Renogy unit on a shelf waiting for my van to arrive 2/10 according to Ford. I don't know a definitive answer yet either but that has not stopped me from figuring out a best approach to starting out. I will install the electrics and then begin taking measurements and making other observations. One of the measurements will be current on the battery side of the charger while the truck is at idle. That should give me a current level to work with that I can then compare to my loads and battery capacities both of which can be adjusted to support my anticipated use cases within the constraints of the power delivered by the charger being powered by the 250A alternator both at idle and while driving. In my case, I intend to have solar on the roof as the panels are relatively cheap compared to greatly increased battery capacity or retrofitting more alternator capacity. So, I am taking more of a "best approach" since I don't know the exact behaviors of the alternator/charger or an exact handle on my power consumption. I will come to know these things and then I will share what I learn.
 

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Back of the hand calculation based on what @kenryan found it looks like it would take 4 hours to charge your completely depleted 200AH battery pack assuming it can maintain a charge rate of 50A, right? But, the charger will not charge at 50A through all phases of the charge profile no matter what the alternator has available so fully charging will take longer. But fully charging may not be what you need to support your usage.
 

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One thing that a lot of people don't consider is that you can run the engine when running large loads. On my current camper, I have good but not great capacity (350 AH lead acid). I regularly use a hot water kettle, which draws over 1200 watts (100 amps). If I am in a situation where I might run low on electricity, I use my autostart to fire up the engine while running the kettle. On my particular setup, I will get about 80 amps from the alternator, so I am only using 20 amps from the battery. Using a strategy like this can allow you to design a less robust (and less expensive) storage and charging system, and still meet your needs.
 

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In case we decide to extend our stay at a particular location and start to run low on juice, will running the vehicle at idle rpm's be sufficient to charge the house batteries? Also, any positive or negative comments on B to B chargers are welcome. Thanks!
In my experience, the answer is yes. At idle, with the heavy duty alternator and dual start batteries I can draw 40A continuously via my Redarc B2B without the alternator getting any hotter than it does when I'm not drawing 40A. I've let the Transit idle for an hour while the alternator charged at 40A w/o issue, adding 40AH to my 100AH lithium battery.

In fact I've decided that I prefer running the Transit instead of my on-board Onan generator. The Transit is quieter, vibrates less and doesn't smell as bad.

Here's an example of the heavy duty alternator output curve from another thread:


--Mike
 

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One thing you guys are not taking into account, these batteries are not going to supply those currents over a long period of time. For example, starting, your battery can supply 80-100 amps at 12 volts, but as you well know, if you have a motor that cranks but doesn't start, that battery will drain in no time, they aren't designed to supply those currents for long.
I'd be very surprised if you could boil a cup of water.... first you need an invertor that can deliver 1200 watts, next take into account the invertor is not 100% efficient, lets say it's 80% efficient, that means you need 1500 watts in, at 12 volts, that's 125 amps.... How long does it take to boil water.... even a small amount of water, lets say a minute.... can your battery put out 125 amps for a minute???
 

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One thing you guys are not taking into account, these batteries are not going to supply those currents over a long period of time. For example, starting, your battery can supply 80-100 amps at 12 volts, but as you well know, if you have a motor that cranks but doesn't start, that battery will drain in no time, they aren't designed to supply those currents for long.
I'd be very surprised if you could boil a cup of water.... first you need an invertor that can deliver 1200 watts, next take into account the invertor is not 100% efficient, lets say it's 80% efficient, that means you need 1500 watts in, at 12 volts, that's 125 amps.... How long does it take to boil water.... even a small amount of water, lets say a minute.... can your battery put out 125 amps for a minute???
Yes, no problem. You just need to have a large enough battery. On my current camper I have 350 AH lead acid battery and 2500 watt inverter. There is no issue at all operating the very high draw water kettle. On my previous camper, I had 225 AH lead acid battery and 2000 watt inverter. That system would also operate the water kettle, but it would cause the inverter to give me a low voltage warning, but it would not shut down. Of course, as soon as the load is removed, the battery voltage rises back up.
 

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One thing you guys are not taking into account, these batteries are not going to supply those currents over a long period of time. For example, starting, your battery can supply 80-100 amps at 12 volts, but as you well know, if you have a motor that cranks but doesn't start, that battery will drain in no time, they aren't designed to supply those currents for long.
I'd be very surprised if you could boil a cup of water.... first you need an invertor that can deliver 1200 watts, next take into account the invertor is not 100% efficient, lets say it's 80% efficient, that means you need 1500 watts in, at 12 volts, that's 125 amps.... How long does it take to boil water.... even a small amount of water, lets say a minute.... can your battery put out 125 amps for a minute???
I have a 1000 watt house inverter, a 255 amp-hr AGM battery and a "600 watt" (actual 950 watts) microwave. Can boil water in the microwave. Microwave uses about 1% of the battery capacity for every 2 minutes of operation.
 

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One thing you guys are not taking into account, these batteries are not going to supply those currents over a long period of time.
I'm not taking into account boiling water with batteries or any other high draw situation as I am not planning to support that use case. I don't plan to have an inverter. All my use cases are relatively low draw 12v. I'm just camping with a CPAP. a small fridge, and a couple LED lights.
 

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Discussion Starter · #19 ·
Lots of informative replies.....thanks for your help!!!
 

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To answer the question in your title... My Ctek D250S B2B charger definitely charges my house battery at idle.
 
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