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Old 07-21-2019, 08:11 AM   #1
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Smart Isolator

In researching battery isolators to charge house batteries off start batteries, it seems that one of the limitations of the isolator is its lack of multi stage charging. Thus, if my house bank is agm, the isolator will not charge it beyond 80%.

Question: If I connect my isolator to a bus bar (see diagram), which is connected to a smart inverter/charger, will the incoming charge pass through the converter and charge the house batteries to 100%?

Joe
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Old 07-21-2019, 09:12 AM   #2
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I had the same problem and solved it with one of these:
Sterling BB1230-12 Volt, 30 Amps - Pro Batt Ultra Battery to Battery Charger

They are available on fleabay and amazon. I've had mine about a year now and find it quite satisfactory.
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Old 07-21-2019, 09:52 AM   #3
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That is so cool! Thanx for the lead.
https://www.sterling-power-usa.com/S...rycharger.aspx
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Old 07-21-2019, 10:29 AM   #4
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Quote:
Originally Posted by TeacherJoe View Post
In researching battery isolators to charge house batteries off start batteries, it seems that one of the limitations of the isolator is its lack of multi stage charging.
OK some common misconceptions here.

First despite terminology nothing is (or should be) charging from battery to battery.

The combiner (VSR, ACR) should only combine the two circuits when a charge source - alt, solar, genset etc - is active.

Those are the actual charge sources.

2 Therefore the combiner is just a switch, open/close based on voltage level. It is not doing any charging, no regulation, just passes through whatever voltage and current the source puts out.

IOW nothing to do with the stages, or charge profile. Classified a "voltage following" device.

As with any device, adds some (usually just a tiny) voltage drop.

____

> Question: If I connect my isolator to a bus bar (see diagram), which is connected to a smart inverter/charger, will the incoming charge pass through the converter and charge the house batteries to 100%?

Best practice is all significant sources get put directly to the House bank. It is your job to adjust the charge profile parameters, then verify with an ammeter to ensure House is getting to 100% Full before the source drops to Float.

The VSR is only used to keep Starter topped up, a trivial task.


_____
Only if a source is incapable of proper charging (stock alt, dumb VR, not worth upfitting with better one)

or if voltage drop is too high, fat enough wiring over too great a distance judged too expensive

is a DC-DC charger like Sterling required.
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Old 07-21-2019, 10:34 AM   #5
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If you do invest in a Sterling, get a BB-series unit, fully user-custom adjustable setpoints.

Make sure to buy from a dealer with good support.

I reco RC (Rod) Collins, aka Maine Sail, Compass Marine compassmarineservices@gmail.com read his articles at http://marinehowto.com

also Alan at Bay Marine Supply, San Diego, CA
https://baymarinesupply.com/
619-320-5899, eBay seller bay-marine, also Amazon, but better to buy direct.
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Old 07-21-2019, 11:23 AM   #6
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Quote:
Originally Posted by john61ct View Post
If you do invest in a Sterling, get a BB-series unit, fully user-custom adjustable setpoints.

Make sure to buy from a dealer with good support.

I reco RC (Rod) Collins, aka Maine Sail, Compass Marine compassmarineservices@gmail.com read his articles at http://marinehowto.com

also Alan at Bay Marine Supply, San Diego, CA
https://baymarinesupply.com/
619-320-5899, eBay seller bay-marine, also Amazon, but better to buy direct.
I think I get it. Thanks. It seems I need the Sterling BB model (30a or 60a? I have a 320a alternator) because I have no other way to manage the B2B charging.

Joe
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Old 07-21-2019, 11:30 AM   #7
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That is possibly true, but IMO not necessarily.

If you want to explore other option, give more detail about your charge sources, batteries, wiring layout / distances involved, measured volts & amps etc

and try to come up with questions.
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Old 07-21-2019, 11:53 AM   #8
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Quote:
Originally Posted by john61ct View Post
That is possibly true, but IMO not necessarily.

If you want to explore other option, give more detail about your charge sources, batteries, wiring layout / distances involved, measured volts & amps etc

and try to come up with questions.
I appreciate your time. My build is still hypothetical, though I have purchased some components.

Battery bank: 400-600ah agm (not purchased)
Charge sources:
3400w generator
30a shore
200w solar
B2B (under discussion)
Output
12v distribution panel (lights, pump, etc)
120v distribution panel (20a mini split circuit, outlets)
2500w Aims inverter/charger

The house batteries will be in a battery box under the bus. The rest of the affair will be about 4-6 feet away in the living area. The solar will be a portable suitcase. The distances are all relatively modest as the living space is 14.5 feet long.

My intent in asking about the battery isolator was to take advantage of drive time to charge the house batteries. In researching that, I saw a huge range of devices - thus my post. I was hoping that since I have invested in a high quality and robust inverter/charger that I could run a simple (dumb) 12v source through the bus bar to the charger and manage the charging with an existing solution.

My question then is whether there is a cheaper way to accomplish B2B charging in a way that brings the house bank to 100% soc.

Joe
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Old 07-21-2019, 11:57 AM   #9
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"it seems that one of the limitations of the isolator is its lack of multi stage charging." Indeed. This is the reason for the Steerling B to B unit. Just as a further note some alternators (like mine) will not "see" a need to charge signal when hooked up to a battery isolator. The problem is further exacerbated by a variety of multiplex wiring systems which are becoming more and more common these days--for example, the ground wire for my low beam headlights becomes the hot wire for my high beam headlamps. It took me a while to figure that out when I installed high beam associated driving lights in my bus.
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Old 07-21-2019, 12:17 PM   #10
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Here's a slightly outrageous question:

Is it possible with a 60a B2B charger to get enough power to the house batteries and through the 2500w inverter to run the 12k btu mini split while driving and charge the house batteries as well?

The bus has a 320w alternator, and there is no engine driven a/c.

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