single 12v or dual 6v batts?

[yeloduster]

Originally Posted by RKCRLR

Would this work if you have two 100AH batteries and a generator? My concern would be damaging the shunt or reducing the current when starting the generator.

I'm sure your won't ruin the shunt. The shunt is a .00075 oum resistor that is about a 1/2" wide piece of metal calibrated with a small slot cut into it. It can handle a lot of amps.

[Stircrazy1]

Originally Posted by yeloduster

I don't think so, buy a $30 battery monitor from Amazon. It will tell you all you really need to know. Click on this Battery Monitor. I use 2 of these. One reports charge current and power the other reports discharge current and power.

See the attachment to see my installation.

Much of what the internal bluetooth monitors report is relative unimportant. Internal monitors tend to be inaccurate when reporting power if the current flow is low.

I prefer my two meters. They are accurate and I don't need to know unless I am in the motorhome. If I am in the motorhome I can just look at the monitors.

this doesn't realy tell you much about what you need to know with LiFePO4 and it won't let you adjust BMS values if the manufacture allows it.

what you can see with the Bluetooth is bvery important especialy for someone who doesn't fully charge their batter to 100% every time and only does it once and a while. with a LiFePO4 the actual cell ballance is very important as over time it can go out and reduce your capacity, to fix this the BMS will balance the battery cells but only once it is at a spicif voltage and it can take a while to do it. the Bluetooth app will let you moniter the individual cell voltage among other things to see the state of your battery.

do I use a simple shunt based battery monitor also, yes I do but that is just for a quick glance of the system with out having to open my phone, they don't tell you anything about the battery its self, only amps in amps out and curent capacity and draw or charge.

[RKCRLR]

Originally Posted by yeloduster

I'm sure your won't ruin the shunt. The shunt is a .00075 oum resistor that is about a 1/2" wide piece of metal calibrated with a small slot cut into it. It can handle a lot of amps.

So what does the 100 amp limit mean? I.e., if I start my generator it doesn't track the current that exceeds 100 amps during cranking?

[yeloduster]

Originally Posted by RKCRLR

So what does the 100 amp limit mean? I.e., if I start my generator it doesn't track the current that exceeds 100 amps during cranking?

If you are talking about the limit of a meter reading the current across a shunt, the limit is the internal limits of the meter. An ammeter that uses a shunt is really a voltmeter. The shunt is a very low value resistor. In the case of the meter I referenced above the shunt is a 75mv (.075V) When 100A is flowing through the shunt, the voltage measured from one end of the shunt to the other is 75MV. The meter measures the voltage and converts the READING to AMPS. The same shunt used in the 100A meter is used by the same company's 200A meter. At 200A the voltage on the shunt would be 150mv. The meter is capable of measuring the higher voltage and display up to 200A.

If you are talking about the 100A limit of the BMS (Battery Management System) inside the battery, it is electronics inside the battery that monitor the current in and out of the battery. If the current in or out of the battery exceeds 100A the BMS will shut off the battery and allow NO current flow. Usually the BMS will turn the battery back on if the right conditions are met. Each battery manufacturer has their own BMS design so specifics questions need to be directed to the specific battery.

I truly hope my poorly worded explanation helps someone!

[Stircrazy1]

Originally Posted by yeloduster

If you are talking about the 100A limit of the BMS (Battery Management System) inside the battery, it is electronics inside the battery that monitor the current in and out of the battery. If the current in or out of the battery exceeds 100A the BMS will shut off the battery and allow NO current flow. Usually the BMS will turn the battery back on if the right conditions are met. Each battery manufacturer has their own BMS design so specifics questions need to be directed to the specific battery.

keep in mind there are "overcurrent protection" built in and most if not all BMS will allow a surge current for a specific period of time then they will shut the flow off, there is also a chance that 100Amp BMS will run 100amps continuously. but most will have a overcurrent value where they will run 200 amps for 5 seconds and 300 amps for 2 seconds. (those numbers are just made up for an example)

so when you see 100amp BMS it is the amprage it can run continiously.

where this comes into play is of you run inverters or high dc loads. so lets say electric jacks on a truck camper. they can pull over 150 amps if you run all 4 at once, so if your battery is a 100 amp BMS you better get two to split the load properly.

[Plug Ugly]

Originally Posted by Stircrazy1

where this comes into play is of you run inverters or high dc loads. so lets say electric jacks on a truck camper. they can pull over 150 amps if you run all 4 at once, so if your battery is a 100 amp BMS you better get two to split the load properly.

thats good to know. thank you.


any good resources out there to learn the do's and dont's of lifepo? i have to admit, id really like to just throw the batt in my camper, leave it hooked up to solar, and be able to foreget about, but it seems like this shouldnt be done with lifepo? (and yes, i understand it was my neglect that killed my wet battery to begin with)

[RKCRLR]

Originally Posted by yeloduster

If you are talking about the limit of a meter reading the current across a shunt, the limit is the internal limits of the meter. An ammeter that uses a shunt is really a voltmeter. The shunt is a very low value resistor. In the case of the meter I referenced above the shunt is a 75mv (.075V) When 100A is flowing through the shunt, the voltage measured from one end of the shunt to the other is 75MV. The meter measures the voltage and converts the READING to AMPS. The same shunt used in the 100A meter is used by the same company's 200A meter. At 200A the voltage on the shunt would be 150mv. The meter is capable of measuring the higher voltage and display up to 200A.

If you are talking about the 100A limit of the BMS (Battery Management System) inside the battery, it is electronics inside the battery that monitor the current in and out of the battery. If the current in or out of the battery exceeds 100A the BMS will shut off the battery and allow NO current flow. Usually the BMS will turn the battery back on if the right conditions are met. Each battery manufacturer has their own BMS design so specifics questions need to be directed to the specific battery.

I truly hope my poorly worded explanation helps someone!

I am trying to understand if the meter will still accurately determine the remaining state of charge of my LiFePO4 batteries if I start my generator several times. My LiFePO4 batteries can start my generator but it does draw more than 100 amps when cranking.

[Stircrazy1]

Originally Posted by Plug Ugly

thats good to know. thank you.


any good resources out there to learn the do's and dont's of lifepo? i have to admit, id really like to just throw the batt in my camper, leave it hooked up to solar, and be able to foreget about, but it seems like this shouldnt be done with lifepo? (and yes, i understand it was my neglect that killed my wet battery to begin with)

all the good to know with LiFePO4 is in the selection and setup. so selecting the right side and making sure you can charge it properly.

floating a lifepo4 at say 13.6 won't hurt it is it will have some load so it does a tiny bit of discharge and charge. it is when sitting at full capacity for over 3 or 4 months with out any movement in State of charge that they say to avoid. but even this it is starting to become debatable if it is that harmful. what it affects is the cycle life so for the average person your cheep lifepo4 from redodo has 4000 cycles so if you cycle that once a week that is 76 years worth of cycles. do twice a week 38 year, 4 times a week19 years and so on. now if you are leaving it at 100% it will reduce that cycle life a little so lets say you only get 3000 cycles instead of 4000, thats a 25% reduction in life so thats only 14 years life at 4 cycles a week, but we are cycleing it every week so it isn't in storage mode so we won't get that drastic of a reduction, and if we are shallow discharging and only useing 50% of the capacity because of the way we set up our capacity then we should gain some cycle life.

what I do when I am camping is I charge to 14.6V then after the adsorbtion period it drops to 13.6V for a float volatage. my solar keeps it charged when I am capmping so every night a bit of the battery is being used and it is recharged the next day so it is always cycleing albeit very small cycle as I have a 9 day capacity incase somthing happens with the solar.
when I am not camping I just change the numbers in my solar controler so it only charges up to 70% and sits there. (I just change the charge voltage to a constant value of my choosing) then a day or two before I go camping I put it back to 100% charge. to do this though you have to make sure you have enough solar and a controler that will let you customize the values in a charge profile. so if you have it on a seasonal site just the day you are leaving bluetooth into the solaar controler and set the charge volatage to say 13.3V and when you come back put it back to 14.6V. takes a couple seconds and if you have enough capacity and solar you won't notice anything as it will charge as you use it.

once you have all this set up then all you have to do is forget about it and manybe check on it once and a while to make sure the other stuff is working.

a LifePO4 is made to cycle from 100% to 0% so you won't kill it from using to much capacity, it doesnt use water so there is nothing to check there, it is basicly as close to plug in and forget as you can get as long as you set up the support right.

[yeloduster]

Originally Posted by RKCRLR

I am trying to understand if the meter will still accurately determine the remaining state of charge of my LiFePO4 batteries if I start my generator several times. My LiFePO4 batteries can start my generator but it does draw more than 100 amps when cranking.

Traditionally SOC (State of Charge) has been determined by measuring the voltage of the battery. The main problem with that method is that the voltage measured is only valid if the battery has been at rest for more than 2 hours.

LifePo4 batteries have the same time restriction the difference between fully charged and discharged is really small so the voltage doesn't mean much.

I think a better way to measure SOC in a LifePo4 battery is to track the wattage out over time. My LifePo4 battery is rated to deliver 2944 Watt Hours. The meter I referred to earlier tracks Watt Hours.

See the attached chart. I related the SOC to the amount of Watt Hours used. The meter does not directly report SOC but it give me the necessary information to make an educated guess.

[Stircrazy1]

Originally Posted by yeloduster

Traditionally SOC (State of Charge) has been determined by measuring the voltage of the battery. The main problem with that method is that the voltage measured is only valid if the battery has been at rest for more than 2 hours.

LifePo4 batteries have the same time restriction the difference between fully charged and discharged is really small so the voltage doesn't mean much.

I think a better way to measure SOC in a LifePo4 battery is to track the wattage out over time. My LifePo4 battery is rated to deliver 2944 Watt Hours. The meter I referred to earlier tracks Watt Hours.

See the attached chart. I related the SOC to the amount of Watt Hours used. The meter does not directly report SOC but it give me the necessary information to make an educated guess.

there are charts that do voltage onder load for stat of charge, but even then it has to be a specific sized load to be 100% accurate. I still use voltage if I am troubkle shooting as it is close enough as long as the load is very small or zero. for the every day use I don't like watt hours as nothing for rv's is realy rated that way, My shunt based meter will show me AH remaining and % of SOC as well as some other things like amps in or out , charging or discharging and so on. for 50 bucks its all I need and I don't have to refer to written down charts or do conversions.