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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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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.

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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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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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Old 07-21-2019, 12:24 PM   #11
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Quote:
Originally Posted by TeacherJoe View Post
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.
Again, the B2B approach is only needed if

your actual charge sources do not match the needs of your House bank, or

you have too much voltage drop from too-thin gauge wiring.

Downside besides cost, is limiting charge current.

_____
As I said, putting alt output directly to the House bank is better, but then you need to give the alt a smart external VR so you can ensure getting to 100% Full, and also not overcharging.

Balmar MC-614 is a good choice.

Then a plain IGN solenoid, maybe $50 will handle bus loads and keeping Starter topped up from the House circuit. Just ensure Starter batt voltage specs are similar to those of House.

A combiner (VSR/ACR) don't use "isolator" that implies diode-based, huge V drop

would add ability to charge Starter from solar / genset etc but you should not need that.

____
For deep cycling AGM, in the US market, go with Lifeline, Odyssey or Northstar, call them to ask about dealers local to you.

Firefly Oasis is good but high cost, only justified if you won't be able to frequently get back to 100% Full. Also withstands regularly drawing below 50% SoC, not a good idea with other makes. Backordered a few months, plan ahead if you go that way.

Full River not bad if that turns out to be a lot cheaper delivered cost per Ah capacity.
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Old 07-21-2019, 12:34 PM   #12
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Quote:
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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.
Nothing to do with DC-DC charging, loads run direct off the bank, and again, why put the alt output current through the B2B bottleneck?

The inverter is a separate issue, only a better quality one will get up to its rated output for long periods, so test that with the aircon unit first.

Likely you'll need a soft start for peak startup power required, check out Coastal Climate Control in MD.

Use a Watt's Up or other Ah totalizer to see whether the load's power usage per hour is matched by the actual alt output at driving speeds. Both factors will of course vary with ambient temps, how well sealed & insulated the cooled space is, etc.
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Old 07-21-2019, 01:10 PM   #13
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Very interesting thread. Thanks to everyone who has posted.
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Old 07-21-2019, 04:44 PM   #14
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As I continue to research, I see this product. It looks it it can be both a dc to dc charger from alternator to house batteries AND an MPPT solar controller. Any comments?

Joe

https://www.amazon.com/CTEK-40-186-D.../dp/B005LBCVL4
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Old 07-21-2019, 04:52 PM   #15
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Well, the first thing I notice is that you need to buy a CTEK 40-185 SmartPass 120 A Energy Management Unit for $300 before you can do both the things you want to do. Still looking at the rest.
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Old 07-21-2019, 04:57 PM   #16
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CTEK makes great products, very robust.

The DCDC output is

limited to 20A while regulating, the add-on just gives a pass-through voltage-following 80A bypass

not setpoint adjustable, I think fixed at 14.4V?

The MPPT solar part. is not nearly as good as most dedicated SCs.
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Old 07-21-2019, 05:06 PM   #17
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Yes, CTEK looks interesting. Under my one step at a time program, I think this will both do me for a while and be useful after:

https://www.amazon.com/CTEK-56-158-A.../dp/B000FQBWCY
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Old 07-21-2019, 07:39 PM   #18
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you probably can run a mini split while you are driving, but it aint gonna keep you cool in hoit weather... engine driven A/C for driving is what will keep you cool driving.. a minisplit will keep you cool while parked and window shades closed..


so i dont understand how an isolator wont charge your batteries over 80%?


my isolator turns on when I start the engine and the system voltage goes above 12.6,and it turns off if the system voltage drops below 11.9. (or in my case I have it wired to turn off when the key is off...)..


with proper wiring your batteries should charge up just fine... with improper wiring you incur voltage drop and wont charge the house batteries up...



-Christopher
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Old 07-23-2019, 07:58 PM   #19
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This seems ok?

Joe

https://www.amazon.com/Blue-Sea-Syst...ea+7622&sr=8-1
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Old 07-23-2019, 09:08 PM   #20
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yep that be good stuff there

I had #7624 in my notes, might want to check the Blue Sea datasheets see what the difference is
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