Sterling BB1230 B2B Charger Not Working

wdavi014 said:

The BB is wired to shunt in the same way, but for some reason, it shows a negative current (-1 amp) when it powers on. I'm thinking this is its quiescent power that's required to run the fan, lights, etc.).

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Here's what i think is happening ... and your "loads" current flow would only add to the blue back-flow.



This is why having the house batteries' negative leads current split across multiple pathways will confuse the shunt.

Once you remove the house-to-chassis wire, the Green flow will become the only one that matters.
It's quite likely that your current situation is mildly charging the two house batts at different rates.

--dick (shunts have to have resistance to develop their 100 millivolt drop (at full load))

Shunts usually drop 50 mV at max load. If OP has a 500A shunt, then shunt resistance is:

R = .05 V / 500 A = 0.1 mohm

The positive cable is greater than 6 mohm. The shunt (most likely) has no effect on current division.

autostaretx said:

--dick (shunts have to have resistance to develop their 100 millivolt drop (at full load))

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calbiker said:

Shunts usually drop 50 mV at max load.

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Before i tried to buy one, that was my assumption, too.
Then i found far more with 100 mv shunts than i was finding with 50 mv.

The shunt (most likely) has no effect on current division.

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I think even if it was a piece of wire, current would go in quaintly "random" directions to create the -1 amp reading.
Heck, we don't know for sure where his shunt's meter is powered from ... that can create an offset, too.
(why i prefer an inductive shunt when "good enough" is good enough)

--dick

You found more 100mV shunts?

I only see 50mV shunts when googling 500A shunt.

https://www.google.com/search?q=500a+shunt&oq=500A+shunt&aqs=chrome.0.0l6.7184j0j8&sourceid=chrome&ie=UTF-8

Even if it's a 100mV shunt, its resistance is only 0.2 mohm

That's still extremely small compared to the 6 awg cable.

Shunts are the most effective and accurate way to measure current. Other methods are sub-standard.

autostaretx said:

Before i tried to buy one, that was my assumption, too.
Then i found far more with 100 mv shunts than i was finding with 50 mv.

--dick

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The battery ground was definitely it folks. I simply disconnected it from the negative battery terminal and the monitor showed that the B2B was in fact charging 25 amps. Thanks for all the support!!! I knew this group would have the answers.

-Warren

My work is done here...

I wouldn't call it done just yet. Do you know the B2B input voltage spec? Some of them stop operation because the input voltage is too low.

I would re-check voltage drops. Measure voltage at starter battery and voltage at the input to the B2B. What's the voltage difference? The alt voltage may drop down to 13.7V after some driving time period. Given the V_drop, will the B2B have adequate input voltage headroom?

wdavi014 said:

The battery ground was definitely it folks. I simply disconnected it from the negative battery terminal and the monitor showed that the B2B was in fact charging 25 amps. Thanks for all the support!!! I knew this group would have the answers.

-Warren

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OrioN said:

My work is done here...

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I think autostaretx gets credit for this one, no? First reply to the original post, although it was useful to have the wiring diagram to confirm.

elemental said:

I think autostaretx gets credit for this one, no? First reply to the original post, although it was useful to have the wiring diagram to confirm.

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I have day job.... but, I found the ground issue, without guessing, nor speculation.

OrioN said:

I have day job.... but, I found the ground issue, without guessing, nor speculation.

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.... by asking a question that had already been asked an answered? I agree with elemental and give credit to autostaretx. "Close thread!"

Returning on-topic: whenever you've set something up and everything *seems* to be working ...
... except the monitor with a negative-side shunt ...
..always suspect/expect that there's a grounding issue bypassing the monitor's sensor.

--dick (who has enough "rules of thumb" that he's definitely in the class of "all thumbs: )

calbiker said:

I wouldn't call it done just yet. Do you know the B2B input voltage spec? Some of them stop operation because the input voltage is too low.

I would re-check voltage drops. Measure voltage at starter battery and voltage at the input to the B2B. What's the voltage difference? The alt voltage may drop down to 13.7V after some driving time period. Given the V_drop, will the B2B have adequate input voltage headroom?

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The voltage drop is somewhere between 0.1 and 0.2 V, but the starter batt voltage isn't constant, as you know, and I don't have the means (long enough leads) to get a more precise measurement. I don't think it's necessary at this point -- it seems to be performing as expected. The input voltage needs to be above 13.2 per the spec which shouldn't be a problem either. Thanks for all the input calbiker.

Robert-NE said:

.... by asking a question that had already been asked an answered? I agree with elemental and give credit to autostaretx. "Close thread!"

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autostaretx said:

Returning on-topic: whenever you've set something up and everything *seems* to be working ...
... except the monitor with a negative-side shunt ...
..always suspect/expect that there's a grounding issue bypassing the monitor's sensor.

--dick (who has enough "rules of thumb" that he's definitely in the class of "all thumbs: )

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Yup, thanks again Dick and everyone else. Had almost zero knowledge of how to do the electrical before this build so it's been fun to learn. Did not fully understand the shunt when I added it later, but I do now

The voltage drop didn't change after lifting the ground connection at the house battery? I'm thinking it should have increased by close to 0.1V. New drop should be somewhere greater than 0.2V.

Doesn't make much difference as B2B low voltage shutdown is at 13.2V. That's the new product spec. Before shutdown voltage was higher and caused problems.

Just so you are aware, if cable voltage drop is 0.2V then the cable dissipates 25A * 0.2V = 5 W

The greater the input cable voltage drop, the lower the house battery charging current. Not a big difference, but can be 1%. That's my perception on how the B2B operates.

wdavi014 said:

The voltage drop is somewhere between 0.1 and 0.2 V, but the starter batt voltage isn't constant, as you know, and I don't have the means (long enough leads) to get a more precise measurement. I don't think it's necessary at this point -- it seems to be performing as expected. The input voltage needs to be above 13.2 per the spec which shouldn't be a problem either.

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calbiker said:

The voltage drop didn't change after lifting the ground connection at the house battery? I'm thinking it should have increased by close to 0.1V. New drop should be somewhere greater than 0.2V.

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I just moved the ground connection from the house battery terminal to the downstream side of the shunt. I also left the negative cable from the starter to the house battery in place, instead of doubling up on the input to the B2B. The manual specifically says to do so, which makes sense because while the chassis is low impedance, there’s probably a fair amount of resistance going all the way back up to the starter ground. Would have used 4 AWG but I had 6, and man, wire ain’t cheap.

All clear. Doubling up gnd is good.

Thanks guys, I had the very same problem with my setup, except that I'm using Ctek D250SA charger instead of sterling.
I had negative Amps when charging from the alternator, but was ok with solar and shore power.
The battery was still recharging, but wasn't taken in consideration by the battery monitor.
I've installed the battery monitor about a year or so after my solar panels and most of my electric system.
My ground cable was still connected to the negative pole of the battery.
Now that is plugged to the "load" side of the shunt, my battery monitor is reading the input Amps..
Hooray,

Cheers guys!!

Nice! Glad to hear it!!