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Old 08-25-2019, 08:30 PM   #1
alysestuck
 
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Default 06 Conversion - Alternator/B-to-B installation Question

Hi everyone!!

Im currently converting a 2006 Dodge Sprinter, ex Fedex fleet. Im on the electrical stage of my van conversion and am a little confused on what to buy for the battery to battery charger according to my battery and alternator.

Ive estimated Id use around 72Ah per day (fan has to run pretty consistently as I have a dog and cat). Im using the Far Out Ride electrical guide. Their calculator says I should have a 220-240Ah battery. Im going to go with a Renogy 200Ah battery since thats what I can afford in my budget.

Instead of an isolator Im going to use a battery to battery (dc to dc) charger. I will hook that up to the alternator. The Far Out Ride calculator suggested I use up to 40A charger based on my battery and alternator. I have a 150A alternator and am likely going to upgrade to a 200A alternator within the next couple weeks.

My question is -
Is the 40A battery to battery charger okay to use based on the alternator power and the battery? What is the difference in charge driving/idling time with a 40A battery to battery charger vs a 20A?

I wont be running solar right now due to budget limitations but plan on it in the future.

Any help is appreciated and I hope Im posting in the right place! ☺️
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Old 08-25-2019, 08:44 PM   #2
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Default Re: 06 Conversion - Alternator/B-to-B installation Question

Quote:
Originally Posted by alysestuck View Post
Hi everyone!!

I’m currently converting a 2006 Dodge Sprinter, ex Fedex fleet. I’m on the electrical stage of my van conversion and am a little confused on what to buy for the battery to battery charger according to my battery and alternator.

I’ve estimated I’d use around 72Ah per day (fan has to run pretty consistently as I have a dog and cat). I’m using the Far Out Ride electrical guide. Their calculator says I should have a 220-240Ah battery. I’m going to go with a Renogy 200Ah battery since that’s what I can afford in my budget.

Instead of an isolator I’m going to use a battery to battery (dc to dc) charger. I will hook that up to the alternator. The Far Out Ride calculator suggested I use up to 40A charger based on my battery and alternator. I have a 150A alternator and am likely going to upgrade to a 200A alternator within the next couple weeks.

My question is -
Is the 40A battery to battery charger okay to use based on the alternator power and the battery? What is the difference in charge driving/idling time with a 40A battery to battery charger vs a 20A?

I won’t be running solar right now due to budget limitations but plan on it in the future.

Any help is appreciated and I hope I’m posting in the right place! ☺️
The specs for B2B chargers generally are the input current, not output. For example a Sterling BB1260 uses about 60A from the alternator and puts out 47A to the house batteries, until it gets hot, when it cuts back to 30A.

My BB1260 runs with the 150A alternator as it waits for a few minutes to start up, which is after the glow plugs shut off. I am not sure you really need a 200A alternator if your B2B can be set up to wait until the glow plugs are done. They take lots of current.

I assume you are going to use Lead Acid batteries. They are somewhat inefficient in charging.
So, it will be worse than the calculations, but for a 200Ah battery, you need to drive for at least 200/20 = 10 hours with a 20Ah B2B to fully charge the battery with a 20A B2B. If you use 72Ah a day, which is reasonable it will take at least 72/20 = 3.6 hours of driving to charge it back up. It will be more because of inefficiencies, so probably more like 4 hours. A 40Ah B2B will do it in 2 hours.

I don't think it is a good idea to idle for that many hours, so enough solar would be very useful.

Regards,

Mark
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Old 08-25-2019, 09:05 PM   #3
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Default Re: 06 Conversion - Alternator/B-to-B installation Question

Hi Mark!

Thanks for the help!! That clears up a lot.

I’ll be using the Renogy 12V 200Ah AGM battery. Do you think the 40A is the way to go then? I’m not sure when I’ll have the funds to get solar so I want to be sure I have enough power and not too much to overdo it with my alternator. I think I’d definitely be able to do the 2 hours of charging per day but I don’t think I’d be driving 4 hours.

Thanks!
Alyse
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Old 08-25-2019, 09:05 PM   #4
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Default Re: 06 Conversion - Alternator/B-to-B installation Question

Renogy recommends a 0.2C charge rate for the battery or 40A, with a max. rate of 80A.

If it was me, and considering that you may increase the battery bank size, I would go with the 60A DC-DC charger (NET 47A battery input).
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Old 08-26-2019, 01:15 PM   #5
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Default Re: 06 Conversion - Alternator/B-to-B installation Question

For an application like this, you will want a battery that can charge very rapidly, especially in the bulk stage.

Rather than renogy's slow charging batteries, consider to buy something like a lifeline or northern. I am more familiar with the lifelines because that is what we use in our van electrical system offerings and they have a very comprehensive technical guide.

As an example of the difference, as Orion pointed out, those charge at ~ 0.2 C vs a lifeline will charge at ~ 2.0 C, taking battery capability largely out of the equation.

In all AGM batteries, there are of course multiple stages of charging required and your decision to use battery to battery charging is a substantial improvement over an ACR approach.

Since you are going to use a B-T-B approach, consider to setup your battery pack as 24 volt. That will help as you add additional loads in the future.

I will just throw this in - usually the 4 power loads on vans are:
- fan
- fridge
- lights
- inverter / cooking

As soon as you add the fridge, you will wish that you had 4 x 100 amp -hrs x 12 volts of storage capacity. The reason is that this will run most RV refrigerators for almost 3 days and help carry you through a weekend of not driving.
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Old 08-26-2019, 01:47 PM   #6
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Default Re: 06 Conversion - Alternator/B-to-B installation Question

There is no reason to upgrade the alternator for a 40/60A charger.
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Old 08-26-2019, 03:23 PM   #7
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Default Re: 06 Conversion - Alternator/B-to-B installation Question

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Originally Posted by Midwestdrifter View Post
There is no reason to upgrade the alternator for a 40/60A charger.
Do you think the 150A alternator would be fine with the 40A charger and 200Ah battery? Id love to not upgrade but was worried this could overwork my alternator.

Thanks!!
Alyse
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Old 08-26-2019, 03:32 PM   #8
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Default Re: 06 Conversion - Alternator/B-to-B installation Question

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Originally Posted by alysestuck View Post
Do you think the 150A alternator would be fine with the 40A charger and 200Ah battery? I’d love to not upgrade but was worried this could overwork my alternator.

Thanks!!
Alyse
The 150A until will have no problem supplying 40A above the chassis loads. Besides, that lead acid battery won't pull 40A for long, even fully discharged it will take 40A for 2 hours tops I would bet.
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