B2B and solar--proper combination?

Hello,

I've mostly finished my conversion-you can see pics here-https://sprinter-source.com/forum/showthread.php?t=77170

We just finished our first real trip, spending 9 days from Seattle through Big Sur. I am really happy with the way everything worked, and now trying to take a little bit of real time experience and further understand and refine my system.

My electrical/charging system consists of a 320W solar panel, a ML-ACR battery combiner, and a Samlex inverter/charger. I have a Victron 100/30 MPPT as well as the BM-712 battery monitor. My batteries are 4 88AH AGM's in parallel(properly balanced).

We mostly boondocked on the trip and were able to operate our lights, 2 fans, water pump, and tea kettle. The lowest the BMV got was 88%, but our only multi day stay was with electrical hookups, so i wasn't able to fully test what the system was truly capable of.

While driving, i would put the ACR on auto and let the alternator bulk charge my house bank. Depending on amp draw, i was seeing anywhere from 13.1 to 13.8 coming from the alternator.I was drawing 25-30A at most. As would be expected, as the battery charge filled up, the amps drawn would lessen and voltage would climb closer to 14V. I typically would switch off the ACR around 95-96% and allow the MPPT to charge the rest of the way. This worked pretty well for me, though my system would typically go into float around 99% with a few AH left to charge. I am still fiddling with the MPPT to see if i could get it to 100%.

I'm curious to hear thoughts of those with more experience. I do understand that some folks prefer DC chargers over the B2B's, and am aware of some of the drawbacks with the B2B's, but would this be the best way to implement the system I currently have?

Not sure what the actual question is?

A B2B is just a subset of the class "DC-DC chargers".

There are not many makes and models, so just ask specific questions about particular models.

My reco is usual one of the Sterling BB series models

If you drive a lot, a B2B has some value, but it seems like your setup is working pretty well?

Renogy recently released an inexpensive 20A B2B, which make a bit more sense for those with smaller banks,

I have the CTEK B2B Charger with integrated MPPT controller, so I never have to worry about switching anything on or off. It’s a multi-stage charger regardless of input, so the batteries are always being taken care of.

Plus, when parked and the solar has charged the house, it will charge the start battery.

The combo of the Dual 250 and SmartPass was about $450; not much more than a separate system of battery and solar, especially in regards to the overall $$$ spent, so it seemed like a no-brainer.

The only drawback is that the MPPT is limited to 22v, designers for 12v panels like Renogy’s. I believe the new KISAE units of similar functions can handle the voltage from a residential panel.

Still, I’m all electric and a 120v dorm fridge, and back to 100% by noon at the latest (300w solar). The last van I did has 200w and the domestic combo sink/stove, so she makes her espresso on the stovetop, and she’s up to full by mid morning.

The Sterling’s are great units; if they added a solar controller it would be a winning combo.


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I apologize if my question wasn't clear. I have the Blue Sea ML-ACR as my B2B, and the Victron MPPT 100/30. I am trying to maximize my systems performance and was asking if there were any obvious pitfalls in the way i have it implemented. My batteries like to be charged at @14.5V and for the most part i am hitting them around 13-13.5 when using the alternator.

If i continue to use my system the way i currently am, bulk charging through alternator and topping off through MPPT, am i compromising battery life? Are there any tweaks with the current system that anyone would recommend?

Sorry if my reply was confusing. I think you’re fine as is, my comment was more along the lines of the only pitfall being having to remember to disconnect and reconnect the Blue Sea.

As far as battery performance/life, seems like you’re doing the optimal for your equipment.


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If you want to keep the batteries at a higher voltage without needing to depend on solar, you could replace the "battery combiner" with a "battery to battery charger" and then get fully programmable charge cycles. I love my https://www.donrowe.com/KISAE-DMT1250-Abso-50A-DC-DC-Battery-Charger-p/dmt1250.htm It's more expensive than the combiner, but was necessary for my lithium batteries anyway. You might have more of a choice with AGM, I'm not up to speed on AGM and voltage/battery life tradeoffs. Just thought I'd throw this Kisae unit out as another option

Ianmoore said:

My batteries like to be charged at @14.5V and for the most part i am hitting them around 13-13.5 when using the alternator.

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The bottom line is you should be getting the bank to 100% Full - confirmed using measured endAmps being reached before dropping to Float.

If this happens only once a week you will suffer some reduced life cycles, the ideal would be every other cycle or so.

If your alternator is outputting too low a voltage, no problem, as long as that is not the source you are relying on for the finishing stages of the charge cycle.

But if it is, then either go to a DC-DC charger, or accept replacing your bank a bit more frequently.

Thanks guys. this is in line with what i was thinking. I'm going to tweak the MPPT to try to get it to charge fully. I do understand the difference between my combiner and the DC to DC units, but want to stick with my system for the time being to see if i can get it to perform well before i consider making a change.

Ianmoore said:

Thanks guys. this is in line with what i was thinking. I'm going to tweak the MPPT to try to get it to charge fully. I do understand the difference between my combiner and the DC to DC units, but want to stick with my system for the time being to see if i can get it to perform well before i consider making a change.

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Depending on much you drive, the DC to DC units may never get your bank to full anyways and often the ACR 'bulks' up the bank quicker.

OrioN said:

Depending on much you drive, the DC to DC units may never get your bank to full anyways and often the ACR 'bulks' up the bank quicker.

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Thanks OrioN. This is why i posted the question. That is interesting to hear about the B2B's being able to more quickly fill up the charge. I was wondering about that, as well as what effect the act of charging at a lower voltage (@mid 13V) as opposed to battery recommended mid 14V would have on the life of the battery.

I know a decent amount about electronics, though my knowledge sits in other areas. The crash course on battery life is like a separate masters course<g

If you add a small inverter to the vehicle battery / alternator, the samlex inverter charger could be plugged into it while driving.

why aren't you using lithium ion batteries? the agms will be toast if you discharge below 50%, lithium will not hence a 40 amp hour lithium is equal to 80 amp agm. plus lighter smaller and they last longer.

turbo911 said:

why aren't you using lithium ion batteries? the agms will be toast if you discharge below 50%, lithium will not hence a 40 amp hour lithium is equal to 80 amp agm. plus lighter smaller and they last longer.

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Discharging lead acid batteries below 50% is optional.

turbo911 said:

why aren't you using lithium ion batteries? the agms will be toast if you discharge below 50%, lithium will not hence a 40 amp hour lithium is equal to 80 amp agm. plus lighter smaller and they last longer.

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And cost, when you include charging equipment, etc, more than double.

I put in 220ah of top of the line AGM’s (Lifeline’s) and a Ctek charging system for a grand.

Just the lithium batteries for that capacity would be almost 2 grand.

Not quite worth it for me yet.


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GSWatson said:

And cost, when you include charging equipment, etc, more than double.

I put in 220ah of top of the line AGM’s (Lifeline’s) and a Ctek charging system for a grand.

Just the lithium batteries for that capacity would be almost 2 grand.

Not quite worth it for me yet.


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Are you saying the equipment to charge LI's is double the cost of lead acid?

OrioN said:

Are you saying the equipment to charge LI's is double the cost of lead acid?

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No, not necessarily be charging equipment. But back in April when I was pricing out the components, a BattleBorne 100ah was running $1000. Since the AGM’s give me 110 amp hours of usable juice, and I can’t find a llithium the under 100ah easily, two BattleBornes would have run me $2000. And they were not compatible with the CTEK charging system I had purchased, after talking to both Ctek and BattleBorne.


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GSWatson said:

No, not necessarily be charging equipment. But back in April when I was pricing out the components, a BattleBorne 100ah was running $1000. Since the AGM’s give me 110 amp hours of usable juice, and I can’t find a llithium the under 100ah easily, two BattleBornes would have run me $2000. And they were not compatible with the CTEK charging system I had purchased, after talking to both Ctek and BattleBorne.


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Click to expand...

What are the limitations of the Ctek?

GSWatson said:

And cost, when you include charging equipment, etc, more than double.

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Lithium batteries require no special charging equipment. All they need is bulk and off.

You are much better served with user-custom adjustable voltage setpoints.

Pretty sure CTEK doesn't even have canned dip switches