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Cheap LiFePO4 BMS?


jetzi

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10 hours ago, MtB said:

 

Thanks. This is what I thought. 

 

In my thread from about three years ago about determining SoC, Dr Bob was of a different opinion IIRC. He held that cell voltages swing around significantly for a given mid range SoC. (Never minding the hockey sticks at each end of SoC.) Also for a given SoC, rested, no load cell voltage will be different according to whether the last thing to happen to the cell was a charge or a discharge. There used to be a graph on the nordkyndesign.com site illustrating this but I can't find it now that site has been revamped. Maybe it has been discredited. I'd be interested if you notice this effect or agree this effect exists, as a discerning real life user.

 

 

 

Below is the graphs for the last month. Green is the Soc from Ah counting (ie something like what the BMV is calculating) blue is the Soc estimated from cell voltages, and purple is the output the algorithm that combines these, and what appears on the display in the engine room after it's converted to a percentage. You can see that the blue line does correlate reasonably well, long term. I'm not sure about the change from generally being higher than the Ah count to generally being lower, a week or two back. I suspect it may be due to lowering solar output as the weather worsens. (If the current metering read significantly high in 5-15A charge range that we get on a sunny day, for instance, that would explain things.) The other change is that we've been doing more engine running as we're moving more.

 

MP.

Screenshot from 2021-09-11 08-51-25.png

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On 09/09/2021 at 13:33, nicknorman said:

I don’t think the BMV discrepancy is anything to do with the SoC relay settings. I suggest you check that the battery capacity, Peukert and charge efficiency settings are all the same as per BMV #1.

 

And check the wiring. Everything that was on the load side of the first BMV shunt must be moved to the load side of the second BMV shunt. So there should be nothing on the battery side of the second BMV except the load side of the first BMV, and nothing on the load side of the first BMV except the battery side of the second BMV.

 

Hi Nick

 

I wonder if I might possibly pick your brains on another charge-control issue? 

I'm considering how to install my Sterling Pro Batt Ultra (used for connecting to shore power). 

Having put in a control system to stop all four of the routine chargers if I get a high SoC, I've been thinking how this same cease-and-desist control could be had over the Pro Batt charger. 

 

One way I though of was to feed its charge to the engine starter battery, so that it goes via one of the B2Bs, 

But I noticed it has a battery temp sensor which is plugged into the unit via what looks like an RJ45 type connector. This switches off the charger at a temp of 55 degrees, and I'm wondering if I can use this socket and cable to connect to the BMV712. 

 

I don't know what the voltage is that will trip the charger into stopping, and it doesnt say in the manual, but it seems like its at least worth a try.  

I've attached a phot of it below- it has green and red wires, but they are much smaller in size than the wires I've used so far to control the B2B and the MPPT- those ones are I think 18AWG.. 

 

So can I ask- if its feasible, and if I was going to give it a try, where should I attach the two tiny wires? 

 

My best guess would be the red wire joins with the COM wire from the BMS that goes to all the chargers, and the green wire connects to the neg wire that comes from the battery neg to the BMV (via the neg bus bar)

 

 

shore charger control wire.2jpg.jpg

Edited by Tony1
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No sorry that won’t work and might damage the charger. The temperature sensor is probably a thermistor (resistor whose resistance varies with temperature) so the charger will have some low voltage electronics in it that is measuring the resistance. If you stuff 12v into it it’s likely to damage it. The only possibility would be to use a small relay operated by the BMV relay to select between 2 fixed resistors, one of which equates to a temperature of say 20C and one of which equates to a temperature of day 60C.

 

You would have to put a meter on ohms range across the unconnected sensor, measure the resistance having adjusted the temperature of the sensor to the relevant values.

 

I can’t be 100% certain that it is a thermistor sensor, it could be a digital one. But measuring the resistance will let us know if it is. A thermistor will likely have a resistance of a few 1000 ohms, and be the same whichever way round you attach the meter probes. A digital one will have a much higher and asymmetric resistance.

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1 hour ago, Tony1 said:

I'm considering how to install my Sterling Pro Batt Ultra (used for connecting to shore power). 

Having put in a control system to stop all four of the routine chargers if I get a high SoC, I've been thinking how this same cease-and-desist control could be had over the Pro Batt charger.

 

Isn't the Sterling Pro "Batt" Ultra a Battery to Battery charger, so not used for connecting to shore power?

 

I have the Sterling Pro "Charge" Ultra, which is a 240V, ("shorepower"), charger.

 

https://sterling-power.com/products/2015-battery-to-battery-chargers-non-waterproof-drip-proof-ip21

 

https://sterling-power.com/products/pro-charge-ultra

 

In the nicest way, and I am no expert, I'm not sure why you are focussing on High SOC, when high voltage seems to be an "equivalent". I remain reasonably sure that, when charging, if you set the charger/s to go no higher than a particular voltage, then it wont exceed a particular SOC.

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21 minutes ago, Richard10002 said:

 

Isn't the Sterling Pro "Batt" Ultra a Battery to Battery charger, so not used for connecting to shore power?

 

I have the Sterling Pro "Charge" Ultra, which is a 240V, ("shorepower"), charger.

 

https://sterling-power.com/products/2015-battery-to-battery-chargers-non-waterproof-drip-proof-ip21

 

https://sterling-power.com/products/pro-charge-ultra

 

In the nicest way, and I am no expert, I'm not sure why you are focussing on High SOC, when high voltage seems to be an "equivalent". I remain reasonably sure that, when charging, if you set the charger/s to go no higher than a particular voltage, then it wont exceed a particular SOC.

This is to some extent true but not the whole picture. Voltage regulation on these sorts of things tends to be quite “soft”, ie the charge current will start to decrease well before the target voltage is reached. Which doesn’t matter if on shore power, but does matter if you’re using a generator.

 

So if you want to charge as quickly as possible up to a specified SoC, then setting a somewhat higher voltage and having a shutoff at the target SoC is the better way.

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14 minutes ago, nicknorman said:

This is to some extent true but not the whole picture. Voltage regulation on these sorts of things tends to be quite “soft”, ie the charge current will start to decrease well before the target voltage is reached. Which doesn’t matter if on shore power, but does matter if you’re using a generator.

 

So if you want to charge as quickly as possible up to a specified SoC, then setting a somewhat higher voltage and having a shutoff at the target SoC is the better way.

 

Also, according to that American bloke with the strident writing style (lost his website address now), a float charge even below the terminal voltage continues to charge the batts over really long periods of time, so over months and years the SoC tends towards 100%. I don't really see how this can happen but if true, it is a different example of the "softness" of LFP charging theory. 

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Just now, MtB said:

 

Also, according to that American bloke with the strident writing style (lost his website address now), a float charge even below the terminal voltage continues to charge the batts over really long periods of time, so over months and years the SoC tends towards 100%. I don't really see how this can happen but if true, it is a different example of the "softness" of LFP charging theory. 

I don't know how Mike either but then I have a fridge freezer and fan in the composting toilet running 

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12 minutes ago, MtB said:

 

Also, according to that American bloke with the strident writing style (lost his website address now), a float charge even below the terminal voltage continues to charge the batts over really long periods of time, so over months and years the SoC tends towards 100%. I don't really see how this can happen but if true, it is a different example of the "softness" of LFP charging theory. 

 

I don't think those are the circumstances the OP is talking about, (with respect and all that :) ).

 

If I am leaving the boat for more than a day or so, I simply turn off the solar, (switch between panels and controller), and would turn off the shorepower charger if I had one.

 

No charging and no discharge, other than the self discharge, (tiny?), of the batteries.

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1 hour ago, Richard10002 said:

 

Isn't the Sterling Pro "Batt" Ultra a Battery to Battery charger, so not used for connecting to shore power?

 

I have the Sterling Pro "Charge" Ultra, which is a 240V, ("shorepower"), charger.

 

https://sterling-power.com/products/2015-battery-to-battery-chargers-non-waterproof-drip-proof-ip21

 

https://sterling-power.com/products/pro-charge-ultra

 

In the nicest way, and I am no expert, I'm not sure why you are focussing on High SOC, when high voltage seems to be an "equivalent". I remain reasonably sure that, when charging, if you set the charger/s to go no higher than a particular voltage, then it wont exceed a particular SOC.

 

You are correct, my eagle eyed amigo- my unit is actually called the Pro Charge Ultra- its this thing:

 

https://www.force4.co.uk/item/Sterling/Pro-Charge-Ultra-Battery-Chargers/9DP?utm_source=google&utm_medium=base&utm_campaign=base&stock=12161&gclid=CjwKCAjwyvaJBhBpEiwA8d38vCiqcuRpooXJJv4FJCInAFzKRDzXdjboJPcDFm8eXP01JKlsJvRltRoCO8sQAvD_BwE

 

I blame Sterling for putting 'pro' in the names of so many damn products...

 

I'm certainly no expert, thats for sure, so I'm feeling my way through this minefield of electrical terminology with the help of the ever-patient Nick. 

Something he has mentioned, and that I have observed, is that the charging voltage will go higher if you are charging at a higher current.

So if I'm getting about 10 amps of solar charge, my batteries wont go over 13.6 or 13.8v until they are about 95% full, which is higher than I would really like- certainly on a daily basis. 

 

So I cant set a limit of say 13.8v to stop charging, because with a trickle of solar coming in, the SoC will get higher than I would like ito.

The other scenario I've observed, with sunnier weather and double the solar, and when running the engine as well, is that the charging current is sometimes much higher, and in those conditions the charging voltage can easily go up to 13.9 or 14v, whilst the SoC has not yet reached my target of 85%.

 

So from what I've seen, and as Nick has explained, I cant rely 100% on voltage alone to guide me to when the target SoC is reached.

There is a danger in using SoC as a safety disconnect though, which is that it can be fiddled with unexpectedly.

E.g. a few days ago I noticed my batteries were approaching 90% SoC, but I thought I'd let them carry on for a bit, because I knew I was mooring in trees the next day and would get almost no solar. I looked back at them a few minutes later and the SoC said 100%, which was impossible given the charging current going in.

 

I deduced that because my tail current setting was not right, the BMV had prematurely decided the tail current state was reached, and that the batteries were now full, and it had set the SoC to 100% itself. 

I didnt even know that was a thing, so tbh I never totally trust the SoC (especiialy since I also adjusted it downwards for a test a few days ago, and forgot to set it back to its true value), but I'm finding its more helpful in setting up a SoC disconnect than the voltage is- although I do keep an eye on both at the moment, to get a feel for how they change under varying conditions. 

 

The whole SoC control thing is a nice to have, I must say that. Its not a safety measure like a high-voltage disconnect, its more aimed at preserving the batteries by stressing them lees on a day to day basis- and it will allow me to leave the boat unattended for a month at a time (without shore power), with no ill-effects on any electrics.

 

 

 

 

 

 

 

 

 

 

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2 hours ago, nicknorman said:

No sorry that won’t work and might damage the charger. The temperature sensor is probably a thermistor (resistor whose resistance varies with temperature) so the charger will have some low voltage electronics in it that is measuring the resistance. If you stuff 12v into it it’s likely to damage it. The only possibility would be to use a small relay operated by the BMV relay to select between 2 fixed resistors, one of which equates to a temperature of say 20C and one of which equates to a temperature of day 60C.

 

You would have to put a meter on ohms range across the unconnected sensor, measure the resistance having adjusted the temperature of the sensor to the relevant values.

 

I can’t be 100% certain that it is a thermistor sensor, it could be a digital one. But measuring the resistance will let us know if it is. A thermistor will likely have a resistance of a few 1000 ohms, and be the same whichever way round you attach the meter probes. A digital one will have a much higher and asymmetric resistance.

 

Thanks Nick- after my unlikely success in connecting all four charger units to the BMV712 so they all stop at 85%, I think I got carried away. I've started thinking everything can be connected to everything else, and it will just somehow work. 

 

I am worried that since I connected my two BMV units together via the local network feature, they have become self aware, and started altering the SoC just to mess with me.

This was all foreseen in 'The Terminator'.... 

 

 

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2 hours ago, MtB said:

 

Also, according to that American bloke with the strident writing style (lost his website address now), a float charge even below the terminal voltage continues to charge the batts over really long periods of time, so over months and years the SoC tends towards 100%. I don't really see how this can happen but if true, it is a different example of the "softness" of LFP charging theory. 

A float value below the terminal voltage just after charging has finished, will after a while cause more current to flow in as the natural terminal voltage decreases (even without discharge). I find that 13.5v held steadily will eventually cause SoC to get very close to 100%. My float voltages (so that in the event of a heavy load from the boat, the alternator provides the juice) are 13.15 for 50% SoC, 13.25 for 80% SoC and 13.45 for close to 100%  SoC. Which is a roundabout way of saying that eg if you hold the voltage at 13.25, the SoC will eventually settle at around 80%. These values are a lot less than normal charge values of say 14.4v to fully charge. So float is ok, as long as it’s at the correct (and surprisingly low) voltage.

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1 hour ago, Tony1 said:

 

You are correct, my eagle eyed amigo- my unit is actually called the Pro Charge Ultra- its this thing:

 

https://www.force4.co.uk/item/Sterling/Pro-Charge-Ultra-Battery-Chargers/9DP?utm_source=google&utm_medium=base&utm_campaign=base&stock=12161&gclid=CjwKCAjwyvaJBhBpEiwA8d38vCiqcuRpooXJJv4FJCInAFzKRDzXdjboJPcDFm8eXP01JKlsJvRltRoCO8sQAvD_BwE

 

I blame Sterling for putting 'pro' in the names of so many damn products...

 

I'm certainly no expert, thats for sure, so I'm feeling my way through this minefield of electrical terminology with the help of the ever-patient Nick. 

Something he has mentioned, and that I have observed, is that the charging voltage will go higher if you are charging at a higher current.

So if I'm getting about 10 amps of solar charge, my batteries wont go over 13.6 or 13.8v until they are about 95% full, which is higher than I would really like- certainly on a daily basis. 

 

So I cant set a limit of say 13.8v to stop charging, because with a trickle of solar coming in, the SoC will get higher than I would like ito.

The other scenario I've observed, with sunnier weather and double the solar, and when running the engine as well, is that the charging current is sometimes much higher, and in those conditions the charging voltage can easily go up to 13.9 or 14v, whilst the SoC has not yet reached my target of 85%.

 

So from what I've seen, and as Nick has explained, I cant rely 100% on voltage alone to guide me to when the target SoC is reached.

There is a danger in using SoC as a safety disconnect though, which is that it can be fiddled with unexpectedly.

E.g. a few days ago I noticed my batteries were approaching 90% SoC, but I thought I'd let them carry on for a bit, because I knew I was mooring in trees the next day and would get almost no solar. I looked back at them a few minutes later and the SoC said 100%, which was impossible given the charging current going in.

 

I deduced that because my tail current setting was not right, the BMV had prematurely decided the tail current state was reached, and that the batteries were now full, and it had set the SoC to 100% itself. 

I didnt even know that was a thing, so tbh I never totally trust the SoC (especiialy since I also adjusted it downwards for a test a few days ago, and forgot to set it back to its true value), but I'm finding its more helpful in setting up a SoC disconnect than the voltage is- although I do keep an eye on both at the moment, to get a feel for how they change under varying conditions. 

 

The whole SoC control thing is a nice to have, I must say that. Its not a safety measure like a high-voltage disconnect, its more aimed at preserving the batteries by stressing them lees on a day to day basis- and it will allow me to leave the boat unattended for a month at a time (without shore power), with no ill-effects on any electrics.

 

I would set tail current to 5% and “charged voltage” to 0.1v below whatever you have the B2B and MPPT charge voltages set to.
Even with correctly set parameters it is not unexpected for the SoC to jump to 100%, this being the demonstration of how the SoC has drifted away from the correct value and the need to be synchronised at 100% SoC from time to time. Your indication of 90% was perhaps more like an actual 97% hence why it jumped shortly afterwards. That is provided the parameters I mention above were set correctly.

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15 minutes ago, nicknorman said:

A float value below the terminal voltage just after charging has finished, will after a while cause more current to flow in as the natural terminal voltage decreases (even without discharge). I find that 13.5v held steadily will eventually cause SoC to get very close to 100%. My float voltages (so that in the event of a heavy load from the boat, the alternator provides the juice) are 13.15 for 50% SoC, 13.25 for 80% SoC and 13.45 for close to 100%  SoC. Which is a roundabout way of saying that eg if you hold the voltage at 13.25, the SoC will eventually settle at around 80%. These values are a lot less than normal charge values of say 14.4v to fully charge. So float is ok, as long as it’s at the correct (and surprisingly low) voltage.

 

I'm doing this at the moment as well- my float voltages are all set at 13.15, in the (mistaken) belief that it would stop any further charging.  

 

The one B2B I have working at the moment tends not go into float, because I made the bulk phase much longer in my custom settings. My thinking is that because I generally only cruise for about 4 hours tops, I usually want it charging the whole time, to make the most of the engine time and the paltry 45-50 amp charge. 

So in my case it's flat out bulk charging for several hours, then the B2B basically stops because I stop the engine- so no float phase at all, in general. 

With the other B2B running I'll have to rethink that approach a bit, and float charging might become a thing.

 

The MPPTs are a different animal of course- on a sunny day they will sometimes get to their float phase, but early indications are that my SoC disconnect will probably kick in and stop them outright at 85%, before they reach the float phase. 

 

 

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On 12/09/2021 at 16:12, nicknorman said:

I would set tail current to 5% and “charged voltage” to 0.1v below whatever you have the B2B and MPPT charge voltages set to.
Even with correctly set parameters it is not unexpected for the SoC to jump to 100%, this being the demonstration of how the SoC has drifted away from the correct value and the need to be synchronised at 100% SoC from time to time. Your indication of 90% was perhaps more like an actual 97% hence why it jumped shortly afterwards. That is provided the parameters I mention above were set correctly.

 

Hi Nick, once again I'd be very grateful for your advice on a B2B question, if you possibly can.

 

I only have one B2B wired up at the moment, so I've experimented with running my two alternators through that unit (in turn, not together). And with both alternators, I'm struggling to get the expected output from my B2B unit. As it turns out, for the new 90 amp alternator that is actually a good thing, as it can only give about 40-45 amps before it starts to overheat. 

So for that unit I'll leave well alone and be happy with 45 amps on a good day. Its doing what it can, bless it.

 

But the other alternator (the 100 amp one) is a bit more capable. My tests about 6 months ago indicated it could put out 60 amps with no overheating. At  65 amps it overheating to about 90-100 degrees, and at 70 amps it got hot enough to concern me. 

Currently though, at start up using this alternator, the B2B puts out about 40 amps, and at after say 40 mins of running, the current actually falls from the initial 40 ish amps to around 37 amps (It has an internal temp sensor that I think throttles it).

 

So I'm looking for a way to drag out another 25 amps or so from this alternator (that will equate to about 20 amps out of the B2B, as there seems to be about 80% efficiency with these units). 

 

My initial thought is to buy yet another B2B. There is a Sterling unit called the BB1230, that seems to put out about 23-25 amps in good conditions (not sure what it actually takes in, but I know there are some energy losses in it, as well as the |BB1260 model).

It has the same features as the BB1260 (uses the same manual), including the all important remote disconnect, and crucially, it can also be set to half power, so if 23 amps is too much for the alternator, I can try it at say 13 amps instead. 

 

So my thinking is to run the existing BB1260 with a BB1230 in parallel, both from the 100 amp alternator. 

But do you think this would be safe? 

I'm confident you can run the exact same units in parallel, I've even read it somewhere in Sterling literature. But is it still ok when they are rated at say 60mps and 30 amps? 

I've emailed Sterling to ask so hopefully I'll know in the next few days, but I'd be very interested in what you think of it. 

 

 

Edited by Tony1
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It seems surprising and a bit annoying that a 60A B2B only outputs 40A. But the small print quotes the 60A as input current, not output current.

 

Anyway, if I understand correctly you propose one 60A B2B for the small alternator, and two B2Bs (60A and 30A) for the bigger one. Presumably there is a LA battery for each alternator? I’ve no experience of these devices but I can’t see why that should cause a problem. The only  thing I’d say is that it seems quite expensive for a relatively small percentage gain in charging current.

Edited by nicknorman
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2 minutes ago, nicknorman said:

It seems surprising and a bit annoying that a 60A B2B only outputs 40A. But the small print quotes the 60A as input current, not output current.

 

Anyway, if I understand correctly you propose one 60A B2B for the small alternator, and two B2Bs (60A and 30A) for the bigger one. Presumably there is a LA battery for each alternator? I’ve no experience of these devices but I can’t see why that should cause a problem. The only  thing I’d say is that it seems quite expensive for a relatively small percentage gain in charging current.

 

Thanks a lot Nick. I have tried replacing the lead acid source battery, but there was no significant increase in B2B output.

I think their practical output limit is 50 amps anyway, with 60 amps going in.

I have noticed that the casing of the BB1260 unit does get pretty hot after an hour of running, and my favourite theory is that the internal temp sensor is acting so as to reduce the current output from an already measly 40 down to 35-37 amps.

But Sterling's initial response is that this is not the behaviour they would expect from the unit.

I have wondered about tweaking the internal temp sensor tolerance, but there's no info on how/whether that could be done.

I'd be surprised if it is a voltage issue on the alternator side, because both alternators cause the B2B to output similar current (although the 90 amp alternator runs at lower voltage, and that does cause the B2B to put out a few more amps than the 100 amp unit).   

It may be a combination of several factors, and Ed has offered to investigate the cause, checking voltages and currents all over place, testing different configurations etc, plus any online info. 

 

But for me the bottom line is that it might be cheaper to bite the bullet and accept the 40 amps limitation, rather than spend £45 per hour of a professional's time in seeking a solution that might not exist, or be worth the expense to resolve, especially when I have other jobs I would want to use his limited time and his valuable expertise in completing. 

Spending £200 on an additional B2B is an expensive solution, but if Sterling confirm it will at least work ok, then I will get some guaranteed return for the money spent.

20 amps extra is a very modest gain for the money, but if it pushes my charge from 75 ish amps up to 95 amps, it will eventually pay for itself (over a period of years).

 

 

 

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Obviously the B2Bs are fairly inefficient and that lost energy goes as heat, which has to escape somewhere. Are they located in a well-ventilated area? Improving the supply of cool fresh air might be an easy improvement if say they are located in a cupboard.

Edited by nicknorman
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8 minutes ago, nicknorman said:

Obviously the B2Bs are fairly inefficient and that lost energy goes as heat, which has to escape somewhere. Are they located in a well-ventilated area? Improving the supply of cool fresh air might be an easy improvement if say they are located in a cupboard.

 

I wish there was a way I could blow refrigerated at the intakes tbh, as that might solve part of the issue, but my plan is to install a 12v fan that will expel air from the top of the cupboard.

I generally leave the cupboard door open when cruising anyway, and if its closed there are vents at the top and bottom of the door to help air flow, but none of it has so far been enough to keep the B2B from getting pretty warm- so with another BB1260 plus a BB1230, its going to get even warmer in there. 

 

In terms of wiring, I started a little experiment yesterday, but quickly backed off. 

My intention was to connect both B2Bs to the 100 amp alternator in parallel, with the idea of setting one B2B to half power- just to see what the total current would be, and whether the alternator overheated.

 

To connect them, I removed the live cable (ie the one coming in from the starter battery) from the B2B, and then I split that into two, and inserted one of the two ends back into the first B2B.

When I tried to push the second end into the second B2B, there was a loud squealing noise, so I immediately stopped the attempt. 

 

At this point the output cables from both B2Bs were already connected to the pos and neg bus bars, so I assumed that would be ok.

I then reconnected the first B2B only as it had been originally, and it did squeal, which is its start up routine I think.

I cant be sure if the loud squealing was because there were two units starting up at once, or whether it had a different note and might indicate possible damage- but I dont want to wait till Ed's next visit in a week before trying it out. 

 

Was I right in splitting the incoming live cable into two like that, and is it correct to lead the pos and neg cables from each B2B directly to the  pos and neg bus bars? 

 

I dont want to push my luck and break something, but at the same time it seems like a simple connection, even for me....

 

 

 

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2 hours ago, Tony1 said:

 

To connect them, I removed the live cable (ie the one coming in from the starter battery) from the B2B, and then I split that into two, and inserted one of the two ends back into the first B2B.

When I tried to push the second end into the second B2B, there was a loud squealing noise, so I immediately stopped the attempt. 

 

I've just had a google to see if I could find some instructions on how to parallel two of these B2Bs, and lost the will to live..... lots of discussions of B2Bs, but no info on how to parallel.

 

If it is like paralleling batteries, you don't split the incoming live, rather you create a kind of daisy chain.... so my guess is that it was wrong to split the cable. Hopefully, someone here will be able to provide definitive instruction on how to do this, or a link to something on the web.

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5 minutes ago, Richard10002 said:

 

I've just had a google to see if I could find some instructions on how to parallel two of these B2Bs, and lost the will to live..... lots of discussions of B2Bs, but no info on how to parallel.

 

If it is like paralleling batteries, you don't split the incoming live, rather you create a kind of daisy chain.... so my guess is that it was wrong to split the cable. Hopefully, someone here will be able to provide definitive instruction on how to do this, or a link to something on the web.

 

Thanks very much Richard- and I found the same thing, not much practical detail. 

 

I'm torn- I want to get on with trying it out, but I dont want to break them and potentially have no chargers. 

On the plus side, I did describe my approach of splitting the live feed into two, and inserting each end to a B2B, and the support guy said this sounded right - but as we know, its so easy to misunderstand a written description...

I got away with it yesterday at least, so I think I'll give it another try, but this time I'll endure the squealing for a few seconds and see if its just the start up noise that they make....

If I'm wrong and I break the B2Bs, I'm on solar charge only until next wednesday when the expert visits....

That said, the solar is playing a blinder at the moment.

 

 

 

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On 12/09/2021 at 16:12, nicknorman said:

I would set tail current to 5% and “charged voltage” to 0.1v below whatever you have the B2B and MPPT charge voltages set to.
Even with correctly set parameters it is not unexpected for the SoC to jump to 100%, this being the demonstration of how the SoC has drifted away from the correct value and the need to be synchronised at 100% SoC from time to time. Your indication of 90% was perhaps more like an actual 97% hence why it jumped shortly afterwards. That is provided the parameters I mention above were set correctly.

 

5% or 0.5%?

 

5% seems a bit too high to determine end of charge.

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2 hours ago, Richard10002 said:

 

I've just had a google to see if I could find some instructions on how to parallel two of these B2Bs, and lost the will to live..... lots of discussions of B2Bs, but no info on how to parallel.

 

If it is like paralleling batteries, you don't split the incoming live, rather you create a kind of daisy chain.... so my guess is that it was wrong to split the cable. Hopefully, someone here will be able to provide definitive instruction on how to do this, or a link to something on the web.

I would not daisy chain. You don’t want the voltage drop from the first device affecting the second. Take 2 wires from each of battery positive and negative, one to each B2B. Same for the B2B outputs, separate wires to the distribution bus bars.

Edited by nicknorman
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