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Old 09-13-2019, 02:45 PM   #11
Midwestdrifter
 
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Default Re: Sterling BB1230 B2B Charger Not Working

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Originally Posted by wdavi014 View Post
Makes sense; however, the monitor shows charging current when the shore power charger and solar charge controller are charging, and the currents are what I would expect them to be. 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.). I also don't think the BB uses the monitor to determine battery state of charge, but if it did and went straight to float mode, I'd expect the output voltage to be 14.4V and not 13.5V.

Perhaps I should draw up a wiring diagram -- I know the pictures are low-light and hard to see.

-Warren
The alternator and BB charger use the chassis ground for negative return. the other items get there ground/negative from your bus bar, so they will be visible to the monitor.
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Old 09-13-2019, 03:30 PM   #12
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Default Re: Sterling BB1230 B2B Charger Not Working

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Originally Posted by calbiker View Post
OP needs to provide a detailed schematic including noting wire gauge and wire lengths. It's likely a wiring error.

The measured voltages indicate the B2B is functional. He measures 14.0V at the chassis battery and 13.8V at the B2B (hopefully both meter probes are at the correct locations). In other words, there's a 0.2V cable drop. A sizable current is flowing into the B2B!

On a side note, my guess the OP has a voltage measurement error. A 0.2V cable drop is way too big. Looks like 1/0 cable (0.1mohm/ft) between chassis battery and B2B. At 20 feet round trip, that's 2 mohm cable resistance.

Current = Cable drop / cable resistance = 0.2 V / 2 mohm = 100 A

We know there's no 100A. That means the voltmeter measurements are not accurate.
Working on a diagram now. The wire is mostly 6 AWG; that's the stuff running into the B2B from the starter battery which is 9ish feet away. Therefore, 8 mohm which yields 25 amps (expected). There's a short section of 1/0 from the pos busbar to the bank, and the heaviest stuff in the picture is 2/0 (overkill, but it's what I had on hand).

I agree -- I think it's a wiring issue, but I can't find it! I'm no electrician, but perhaps y'all can help me flush out a theory. The output should be close to 25 A, but I'm measuring -1 A (let's assume for a moment that the shunt is working properly, which I don't think is too far of a stretch cause it seems to work for the other chargers). So, could it be possible that there's a 26 A current loss due to an increase in resistance??

V=IR, so if V increases (slightly by 0.2 V), I decreases by 26 A, R would have to increase, right?

If there is a wiring issue, what's a good way to isolate it? Do i just measure resistance at different points?

Thanks everyone for all the input so far! I REALLY appreciate it!
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Old 09-13-2019, 03:45 PM   #13
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Default Re: Sterling BB1230 B2B Charger Not Working

We'll find the problem. Just need an accurate diagram.

We calculate resistance, and measure voltage.

The most accurate way to measure B2B input current is to measure the cable voltage drop. Place the + meter probe directly on the positive chassis battery terminal. Place the - meter probe on the positive input terminal of the B2B. Your probe leads won't be long enough as this distance is 9 ft. You're going to need a longer probe lead. Measure voltage drop (will be less than 0.2V) with alt operational.

Current = Voltage drop / (9 ft * 0.4 mohm/ft) = V_drop / 3.9 mohm

The wiring issue is with your current measurement and shunt wiring.

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If there is a wiring issue, what's a good way to isolate it? Do i just measure resistance at different points?
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Old 09-13-2019, 04:07 PM   #14
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Default Re: Sterling BB1230 B2B Charger Not Working

The easiest way to find out what is happening is with a DC clamp meter.

Just as an example, something like an extech clamp meter with a low current range is what I use for things like that. There are other options, that is just what I have.

The smaller clamp makes it easy to get into tight locations.

Really anyone who has a van electrical system should probably own one, even before they buy a battery soc monitor.
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Old 09-13-2019, 04:37 PM   #15
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Default Re: Sterling BB1230 B2B Charger Not Working

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Originally Posted by Midwestdrifter View Post
The alternator and BB charger use the chassis ground for negative return. the other items get there ground/negative from your bus bar, so they will be visible to the monitor.
Hmm, I don't quite follow, but that's probably due to my lack of electrical knowledge. The B2B negative is connected to the bus bar. The bus bar is connected to the grounded house bank AND the starter battery chassis ground. So doesn't that mean they share a common ground?
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Old 09-13-2019, 04:41 PM   #16
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Default Re: Sterling BB1230 B2B Charger Not Working

Its hard to tell from your photo. On a shunt, NOTHING except the battery is connected to one side. All other connections are made to the load side (not battery side) of the shunt.
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Old 09-13-2019, 04:50 PM   #17
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Default Re: Sterling BB1230 B2B Charger Not Working

Here's the wiring schematic -- hope it doesn't suck too bad. I excluded fuses, breakers, and other stuff that isn't relevant.

Wiring Schematic.jpg

Edit: I also didn't include wire gauge or lengths. I can tell you it's all over-sized and nothing smaller than 6 AWG.

Last edited by wdavi014; 09-13-2019 at 04:52 PM.
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Old 09-13-2019, 04:54 PM   #18
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Default Re: Sterling BB1230 B2B Charger Not Working

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Originally Posted by Midwestdrifter View Post
Its hard to tell from your photo. On a shunt, NOTHING except the battery is connected to one side. All other connections are made to the load side (not battery side) of the shunt.
Yup, will definitely correct that -- probably this evening.
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Old 09-13-2019, 05:19 PM   #19
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Default Re: Sterling BB1230 B2B Charger Not Working

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Yup, will definitely correct that -- probably this evening.
Why is the house bank grounded to the chassis, and before the shunt?









.

Last edited by OrioN; 09-13-2019 at 06:01 PM.
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Old 09-13-2019, 05:33 PM   #20
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Default Re: Sterling BB1230 B2B Charger Not Working

You probably now know what's wrong. The house battery has a direct connect to chassis ground. You have 2 ground paths from starter battery to house battery. You have the 6 gauge ground cable and the chassis ground to Li battery cable.

It turns out that the chassis ground cable has much lower resistance and as a result current is bypassing the shunt.

I would keep the chassis ground cable. Remove it from the Li battery and connect this cable to the negative bus bar. You can remove the cable from starter bat neg to bus bar neg. I would then install this (removed cable) and double up on the positive cable from starter battery. 6 awg really isn't big enough. Double up and you'll be better.
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