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ivan&alice

Cheap LiFePO4 BMS?

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10 minutes ago, Mike the Boilerman said:


Why do you think I don’t?! 
 

 

"I still use the LA bank as my main source of leccy but I can turn the isolator switch ON when I feel like it to bring the Li into service. And turn it OFF to take them out of service and revert to the old LA system. "
 

(or am I quoting the wrong person tracking back through the thread?)

 

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3 minutes ago, ditchcrawler said:

"I still use the LA bank as my main source of leccy but I can turn the isolator switch ON when I feel like it to bring the Li into service. And turn it OFF to take them out of service and revert to the old LA system. "
 

(or am I quoting the wrong person tracking back through the thread?)

 

That's what I thought Mike had said. I think you have it right :) 

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2 hours ago, Richard10002 said:

 

So.... could I:

 

1) buy 2 or 3 of these used 12v 130Ah batteries:

 

https://www.ebay.co.uk/itm/No1-VALENCE-LiFePO4-12V-BATTERY-130Ah-1-6Kwh-U27-12XP-LITHIUM-LI-ION-SOLAR-BANK/264491336668?hash=item3d94e983dc:g:BhwAAOSwXzxddUH3

 

2) Connect them in parallel with my LA bank with an isolator, (presumably, when the isolator connects them it doesnt isolate the LA bank, so all batteries are being charged or used at the same time?).

 

3) Make sure my mains charger and solar systems are set so they cant deliver more than 14.6V, (turn off equalising in the solar). I dont think my alternator can deliver more than 14.4V, and there is a relay which also charges the starter battery.

 

and Bobs your Uncle? 

 

After 1-3 above, I can then start thinking about refinements, in terms of monitoring and control?

Peter has commented on the batteries.

I dont like your high voltages!

I charge up to 13.9V max. That is around 95% SoC if charging at 30A ex my battery charger IP22. If you charge at 14.4V then you must have a disconnect that works faultlessly when the batteries get near 100% which means terminating on both voltage and tail current (as MP does with his Arduino system). I dont know of a commercial system that measures full via voltage and tail current. If you are not using tail current to terminate then best to back off the maximum voltage so you dont exceed 13.9V. 

The key to a quiet life though is to have your charge devices throttle back when getting above 80% SoC (which is around 13.7V at 30A on mine) rather than having to rely on the high/low voltage disconnects activating. Therefore do what Peter says and set the MPPT to go to a float of <13.4V when voltage reaches 13.9V. The alternator is more tricky.

I have a sterling AtoB on mine and I can control the termination voltage via choosing the right setting on that. You will run into big problems if you charge at 14.4V - its just too high unless you have a bomb proof BMS. You need to be able to throttle back the alternator when up to 90%.

If you read a lot of the commercail stuff, they say you can charge at 14.4V but they have a bomb proof BMS.

 

I would be a bit worried about 'drop in' LiFePo4s. Reading all the info on the US cruiser forum, they say most (if not all) drop in Li's have low power switching so they will not take the 200A that may appear - especially if you are paralleled to your start battery (I am not). Peter doesnt see that problem as he doesnt have an engine! The message I read on the cruiser forum is avoid drop ins like the plague.

 

Edited by Dr Bob

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1 hour ago, Richard10002 said:

 

3) Make sure my mains charger and solar systems are set so they cant deliver more than 14.6V, (turn off equalising in the solar). I dont think my alternator can deliver more than 14.4V, and there is a relay which also charges the starter battery.

 

Richard, to help you understand the voltage side more, here is a quick run down of what happens with LiFePo4s.

 

See diagram below.

We tied up in a Marina on Sunday to take our Li's up to 100% to resync the BMV.

So at 10am we put our Victron Ip22 charger on ...30A... on its Li setting. (On the Li setting it puts out 14.1V and doesnt seem to want to go into float. If this was LAs, after 80% charge it would be up to 14.1V)

On LiFePo4s however, the voltage starts low and builds up slowly. So from 10am to 2pm it slowly rose from 13.45V to 13.48V (charger off for a while when we went to the shops). See blue line. At 2pm I guess it the Li bank was at 75% SoC. Current (in orange) pretty stable at 30A. By 1530, we were at around 90% charged and the voltage was starting to rise faster and was about 13.6V. This is usually the point where my alternator controller backs off the output and goes into float below 13.4V. In this case though I was going to force the system to full charge.

At point A, we reach the voltage knee of the total bank and voltage starts to rise faster....but note current is still flat at 30A....maybe 95% charged. At point B, the current now starts to be limited by the batteries and current drops (the graph is marked up wrong!!!). Voltage is still rising fast. We are now at 98% charged. It is essential not to go over 100% SoC so at 13.9V my safety system cuts in and the BMV opens the relay which shuts my BEP motorised switch, isolating the lithiums and allowing any voltage spikes to go into the LAs.

In normal operation, my charge sources would cut back on voltage to below 13.4V when I get to 13.6V (at 30-40A charge) so I never get to point A. If you have charge sources that will go to 14.4V, then the Li's will rise in voltage to 14.4V and get wrecked unless the inbuilt battery BMS (which I would not trust) isolated them. The disconnect is best if it is only used in an emergency.

 

Charging LiFePo4s is totally different to the bulk, absorption and float used in LA's.  The voltage rises as they get charged and it is easy to estimate SoC from the voltage/current.Stop when you get to your target voltage.

 

The trickiest thing about all of this, is how to get your alternator to turn off at 13.6V or at least by 13.9V. My alternator never got above 13.9V so would be fine on its own but I bought a Sterling AtoB to get it to 14.4V for my lead acids and that has multiple settings that let me access max voltages between 13.6V and 13.9V. Tom has a different alternator controller. MP does his control via his Arduino. Peter doesnt have an alternator.

 

Edit - Please note at Point B - it should read 'start of reduction in current' - not voltage.

 

 

Screen Shot 2019-10-22 at 15.37.01.png

Edited by Dr Bob
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1 hour ago, Richard10002 said:

:)

 

Whether what is flashing green or red? Presumably green means they are OK, and red that they are not? It would be just my luck for them to be flashing green on collection, and red on connection :( Clearly, they are just an example I've found, and there would need to be some way of assessing how "used" a particular battery is.

 

The wires coming out of the middle of the casing on the top seem to suggest they need to be connected to some kind of gizmo for BMS

 

I'm just trying to get a grip of how to get started, and whether it is as complicated as it reads, or whether it can be as complicated as you want it to be :)

 

I like Mikes "Baby Steps" idea.

If flashing green all is good, the leads connect to other batteries so that they talk to each other a9a master BMS, I can talk to the batteries with a lead and my old puter. If you buy them you would just charge them to 13.8 volts, that is 80% full and is the ideal top volts for these batteries. In all honesty I have given up checking mine as they are always balanced,  John who has them has never checked his at all! The mantra is 20 80%= long and happy life for LifePo4s 

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25 minutes ago, peterboat said:

If flashing green all is good, the leads connect to other batteries so that they talk to each other a9a master BMS, I can talk to the batteries with a lead and my old puter. If you buy them you would just charge them to 13.8 volts, that is 80% full and is the ideal top volts for these batteries. In all honesty I have given up checking mine as they are always balanced,  John who has them has never checked his at all! The mantra is 20 80%= long and happy life for LifePo4s 

I'm not yet committed, so dont want to waste the guys time, but I asked what they were used for before he got them, and he says he doesn't know. I also asked how many cycles they might have done, and he said, between 417 and 1966. I'm wondering how he can be so precise, and I could ask if he has 3 at the lower end of the cycle numbers. I don't like the sound of a battery which has done 2000 cycles - I think they are rated at 2500 cycles if some of what I've read in various places is correct.

 

My Sterling Pro Charge Ultra, (60A), has a LiFePo4 setting, with a choice of 13.8V High 13.8V Float 13.2V Maintenance, or 14.6V High 14.6V Float and 13.2V Maintenance. So I can comply with the lower voltage requirements and, given that I am running the genny, I am in control of when things stop. Not sure how much use the NASA BM2 Battery Monitor is in these circumstances?

 

In reality, as I am off grid, and use a generator/solar/engine, I could also choose to have them connected to the charger and solar only, thus avoiding the possibility of overcharging with the alternator.

 

I am wondering how Mike charges his Lis and LAs on the same system, given the differing charging voltage requirements. I guess it just needs the discipline of not having the Lis connected when charging the LAs?

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6 minutes ago, Richard10002 said:

I'm not yet committed, so dont want to waste the guys time, but I asked what they were used for before he got them, and he says he doesn't know. I also asked how many cycles they might have done, and he said, between 417 and 1966. I'm wondering how he can be so precise, and I could ask if he has 3 at the lower end of the cycle numbers. I don't like the sound of a battery which has done 2000 cycles - I think they are rated at 2500 cycles if some of what I've read in various places is correct.

 

My Sterling Pro Charge Ultra, (60A), has a LiFePo4 setting, with a choice of 13.8V High 13.8V Float 13.2V Maintenance, or 14.6V High 14.6V Float and 13.2V Maintenance. So I can comply with the lower voltage requirements and, given that I am running the genny, I am in control of when things stop. Not sure how much use the NASA BM2 Battery Monitor is in these circumstances?

 

In reality, as I am off grid, and use a generator/solar/engine, I could also choose to have them connected to the charger and solar only, thus avoiding the possibility of overcharging with the alternator.

 

I am wondering how Mike charges his Lis and LAs on the same system, given the differing charging voltage requirements. I guess it just needs the discipline of not having the Lis connected when charging the LAs?

When you plug them in they tell you how many cycles they have done, These batteries were used in smiths electric vans, and the USA used them in mini subs so they are good. Cycle wise 5000 would be about right at the lower voltage figures. if like me you are off grid these will be a revelation to you like they were to me, I would just connect them up to your LAs if you charge by alternator and monitor the voltages, use the lower settings for the charger and solar. The price he is offering them at is cheap so buy before they are gone!

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24 minutes ago, Richard10002 said:

I'm not yet committed, so dont want to waste the guys time, but I asked what they were used for before he got them, and he says he doesn't know. I also asked how many cycles they might have done, and he said, between 417 and 1966. I'm wondering how he can be so precise, and I could ask if he has 3 at the lower end of the cycle numbers. I don't like the sound of a battery which has done 2000 cycles - I think they are rated at 2500 cycles if some of what I've read in various places is correct.

 

My Sterling Pro Charge Ultra, (60A), has a LiFePo4 setting, with a choice of 13.8V High 13.8V Float 13.2V Maintenance, or 14.6V High 14.6V Float and 13.2V Maintenance. So I can comply with the lower voltage requirements and, given that I am running the genny, I am in control of when things stop. Not sure how much use the NASA BM2 Battery Monitor is in these circumstances?

 

In reality, as I am off grid, and use a generator/solar/engine, I could also choose to have them connected to the charger and solar only, thus avoiding the possibility of overcharging with the alternator.

 

I am wondering how Mike charges his Lis and LAs on the same system, given the differing charging voltage requirements. I guess it just needs the discipline of not having the Lis connected when charging the LAs?

You need your NASA to monitor voltage and current when charging ....and to monitor voltage , Amps and Ahrs out when discharging. Once you know what you are doing, you can estimate SoC from voltage and current but you really dont need to know what the SoC is. Just know your voltage limits. On mine I go from 12.8V to 13.2V (on discharge).....and you can see the voltage SoC relationship on charging in the graph above.

13.8V High and 13.8V float doesnt sound too good. When you reach your target voltage ie 13.8V, it must drop back to <13.4V otherwise you risk overcharging. I dont think Sterling have a clue about LiFePo4s so maybe take their numbers with a pinch of salt. You may well find the voltage does drop back on going to float.

One thing about Li's that is good is you can be certain of how much power is going into the batteries. You will get into a routine. Overnight you maybe 200Ahrs down. The following morning therefore run the genny for 2 hours and if 60A then you will be 80Ahrs down at the end. Turn off genny. Dont even look at the meter. Repeat each day. Never even get to 80% SoC.

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1 hour ago, Dr Bob said:

You need your NASA to monitor voltage and current when charging ....and to monitor voltage , Amps and Ahrs out when discharging. Once you know what you are doing, you can estimate SoC from voltage and current but you really dont need to know what the SoC is. Just know your voltage limits. On mine I go from 12.8V to 13.2V (on discharge).....and you can see the voltage SoC relationship on charging in the graph above.

13.8V High and 13.8V float doesnt sound too good. When you reach your target voltage ie 13.8V, it must drop back to <13.4V otherwise you risk overcharging. I dont think Sterling have a clue about LiFePo4s so maybe take their numbers with a pinch of salt. You may well find the voltage does drop back on going to float.

One thing about Li's that is good is you can be certain of how much power is going into the batteries. You will get into a routine. Overnight you maybe 200Ahrs down. The following morning therefore run the genny for 2 hours and if 60A then you will be 80Ahrs down at the end. Turn off genny. Dont even look at the meter. Repeat each day. Never even get to 80% SoC.

I have a NASA but only look at the voltage amps in and out is of no concern to me. My only issue was the 13.8 volts for to long but I am sure it will be reduced rapidly 

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1 hour ago, Dr Bob said:

13.8V High and 13.8V float doesnt sound too good. When you reach your target voltage ie 13.8V, it must drop back to <13.4V otherwise you risk overcharging. I dont think Sterling have a clue about LiFePo4s so maybe take their numbers with a pinch of salt.

I can actually set a custom setting..... I currently have it set at 15V max and 15V float, (because, using the genny, I don't ever want it to go into float for my LA batteries). Looks like both absorption and float can be set to anything between 12.6V and 15.1V, so I could definitely set 13.8V max, and 13.2V float. I'm guessing I can do the same with my Tracer Solar controller and its MT50 gizmo.

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22 minutes ago, Richard10002 said:

I can actually set a custom setting..... I currently have it set at 15V max and 15V float, (because, using the genny, I don't ever want it to go into float for my LA batteries). Looks like both absorption and float can be set to anything between 12.6V and 15.1V, so I could definitely set 13.8V max, and 13.2V float. I'm guessing I can do the same with my Tracer Solar controller and its MT50 gizmo.

That's good they are very good batteries possibly the best available as they were designed for the American military 

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1 hour ago, Richard10002 said:

I can actually set a custom setting..... I currently have it set at 15V max and 15V float, (because, using the genny, I don't ever want it to go into float for my LA batteries). Looks like both absorption and float can be set to anything between 12.6V and 15.1V, so I could definitely set 13.8V max, and 13.2V float. I'm guessing I can do the same with my Tracer Solar controller and its MT50 gizmo.

That sounds like it will work then.

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21 hours ago, Richard10002 said:

Hard to see it taking off until you can buy batteries and a gizmo or two that you can just connect with a few wires without knowing how it all works?

You pretty much can buy a 'plug & play' system, but you will need to sell both Kidneys, AND an arm AND a leg to be able to buy it.

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5 hours ago, Dr Bob said:

You may well find the voltage does drop back on going to float.

 

Now you have me puzzled.

 

All the Li gurus (Nordkyn, that annoying American bloke) go on at length about how BAD it is to float charge Li batts. In fact leaving Li batts on float is a surefire way to destroy them and is a first class example of the type of LA thinking one needs to leave at the door when setting out on the Li adventure. 

 

One needs to charge them to one's selected voltage, the STOP, apparently, as on float they continue to charge at a very low current and eventually tip over the 100% SoC then overcharge and screw themselves.

 

Peterboat also mentions float charging from time to time.....

 

 

 

 

Edited by Mike the Boilerman
Add a bit

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11 minutes ago, Mike the Boilerman said:

 

Now you have me puzzled.

 

All the Li gurus (Nordkyn, that annoying American bloke) go on at length about how BAD it is to float charge Li batts. In fact leaving Li batts on float is a surefire way to destroy them and is a first class example of the type of LA thinking one needs to leave at the door when setting out on the Li adventure. 

 

One needs to charge them to one's selected voltage, the STOP, apparently, as on float they continue to charge at a very low current and eventually tip over the 100% SoC then overcharge and screw themselves.

 

Peterboat also mentions float charging from time to time.....

 

 

 

 

Yes, the expert wisdom is that you shouldn't float LiFePo4s.

When fully charged the voltage at rest is circa 13.3V. Unfortunately most chargers are designed for LAs so will have a float period when bulk/ absorption finishes. You are ok if that float voltage is below the 13.3 V as no current will flow to the Li's (at least that is the way I read it and it seems to happen that way when my alternator goes into float).

Best not to have any float when at 100% cause you don't want to hold the bank full but I am happy if my alternator or MPPT goes down to 13.2V  to 'float' and I am at 80%. 

You will overcharge Li's if you terminate charge at 100% and then the charger goes into float at 13.7V.

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9 hours ago, Richard10002 said:

I can actually set a custom setting..... I currently have it set at 15V max and 15V float, (because, using the genny, I don't ever want it to go into float for my LA batteries). Looks like both absorption and float can be set to anything between 12.6V and 15.1V, so I could definitely set 13.8V max, and 13.2V float. I'm guessing I can do the same with my Tracer Solar controller and its MT50 gizmo.

I have a 40a sterling charger, and (from memory) have set it to 14.0v bulk, 13.4v absorption, and 13.4v float. Basically so it charges up to 14.0v then cuts off and maintains voltage at 13 4v. Only every used it to test the settings though, why bother running noisy generator to put 40a in when our quieter engine puts 90a+ and gives hot water!

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6 hours ago, Mike the Boilerman said:

 

Now you have me puzzled.

 

All the Li gurus (Nordkyn, that annoying American bloke) go on at length about how BAD it is to float charge Li batts. In fact leaving Li batts on float is a surefire way to destroy them and is a first class example of the type of LA thinking one needs to leave at the door when setting out on the Li adventure. 

 

One needs to charge them to one's selected voltage, the STOP, apparently, as on float they continue to charge at a very low current and eventually tip over the 100% SoC then overcharge and screw themselves.

 

Peterboat also mentions float charging from time to time.....

 

 

 

 

You don't want to float charge them. All the talk about float settings is purely to trick LA based charges to effectively switch off and not put any more charge in. This is best done by terminating charge completely, but as LA charge sources don't usually offer that option, the best alternative is set float value low enough that it has the same effect. With float at 13.2 or 13.3 no charge will enter the Li bank, and they will discharge until approx 80% and stay there. This can clearly be seen on monitoring.

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11 hours ago, peterboat said:

Cycle wise 5000 would be about right at the lower voltage figures.

I've seen cycle life widely quoted as 10,000 if kept within 20-80% soc. If avoiding the extremes, there doesn't really seem to be much of a mechanism for degradation from my reading of the papers. 

11 hours ago, peterboat said:

if like me you are off grid these will be a revelation to you like they were to me, I would just connect them up to your LAs if you charge by alternator and monitor the voltages, use the lower settings for the charger and solar. The price he is offering them at is cheap so buy before they are gone!

Couldn't agree more. 

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4 hours ago, Craig Shelley said:

Firstly, for battery protection, we have a ML-RBS-7713 remote battery switch from Blue Sea Systems. This was quite a pricey piece of kit, but worth it i think. We had to import it from the US, which was a bit of a rigmarole. It is intended to be used where the batteries are inaccessible, and comes with an illuminated remote switch with sliding guard. On the main unit there is a knob which enables it to be locked off or overridden. The really useful thing about this unit is that the on/off control wire behaves as if the switch is a conventional relay, except that it is internally magnetically latched and draws very little current in either state.

That switch was very high on my list when researching what components to use to provide the protection. Ultimately went with the BEP motorised battery switch in the end which has similar control (i.e. single on off wire). Mainly due to price and UK availability. 

 

4 hours ago, Craig Shelley said:

Currently we only have protection for the overall battery pack voltage. I hope to improve this soon. We use a couple of cheap modules which can be found on ebay, search "12v voltage control relay". Two of these modules are used, one upper and one for lower trip points. The trip voltage is configured via the buttons and display. Wires are connected via screw terminals.

This switching/protection scheme was knocked-up quite quickly using off the shelf parts. I would like to revisit this at some point to make it more fail safe, improve the monitoring etc... If the battery voltage exceeds limits, it disconnects the battery and sounds an alarm buzzer.

This is exactly what I planned for a friend's camper, even using the same type of voltage control devices. Unfortunately he's decided not to proceed at present but good to here that it works for you! I've always thought this could be a relatively easy and cheap option for a basic install. 

 

Thanks for your detailed explanation in the alternator mods you've done. Interesting read, even if some of it is beyond my understanding! We currently use an arduno based external regulator, programmed with specific LiFePo4 settings, and using a current shunt as one of the parameters to determine end of charge (and to hold charge current to effectively 0a once charged, yet still support loads),

 

Tom

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9 hours ago, Mike the Boilerman said:

 

Now you have me puzzled.

 

All the Li gurus (Nordkyn, that annoying American bloke) go on at length about how BAD it is to float charge Li batts. In fact leaving Li batts on float is a surefire way to destroy them and is a first class example of the type of LA thinking one needs to leave at the door when setting out on the Li adventure. 

 

One needs to charge them to one's selected voltage, the STOP, apparently, as on float they continue to charge at a very low current and eventually tip over the 100% SoC then overcharge and screw themselves.

 

Peterboat also mentions float charging from time to time.....

 

 

 

 

Mike like the others I have a very low float figure, mine hit 13.9 in bulk go to 13.8 in absorb and then 13.4 float but nothing goes in, my NASA shows no charge, the absorb setting alternates between a couple of amps and zero as well for about an hour

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2 hours ago, Tom and Bex said:

I've seen cycle life widely quoted as 10,000 if kept within 20-80% soc. If avoiding the extremes, there doesn't really seem to be much of a mechanism for degradation from my reading of the papers. 

Couldn't agree more. 

The 5000 cycles down to 80% capacity is what valence claim for the batteries, I have bought 30 x 36 volt valence batteries out of a bus, these were at end of life, they were in various states of charge some were at zero I have charged them all up to 41.7 volts and reset the BMSs they are holding 40 volts ish and have sat for a month holding that charge. They accepted the rated KWhs so only time will tell how good they are on light use driving the boat.

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3 hours ago, Tom and Bex said:

I've seen cycle life widely quoted as 10,000 if kept within 20-80% soc. If avoiding the extremes, there doesn't really seem to be much of a mechanism for degradation from my reading of the papers. 

Couldn't agree more. 

Like you I expect my batteries to do way more than 5000 cycles, but even then I think they will last my lifetime, I am putting a heating pipe through my drive battery boxes which are insulated as well so that if I want to cruise in the cold they will still charge from the solar

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3 hours ago, Tom and Bex said:

Victron BMV?

Yes, the BMV measures it but the relay only operates on voltage, temp or state of charge ....not on two together. It would be great if it could operate on voltage above X and current below Y. Am I missing something?

 

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