LifePO4 3.2V Batteries vs. "Drop in Replacements"

[Hillbilly Heaven]

I do think I will go with the BMS/Monitor and balancers from EPCP. It looks like it would do what I need at a reasonable price. Mains charging will be a Sterling ProCharge Ultra that I have, around 1000watts solar (still need to do this bit) and a Sterling 24v to 12v DC to DC charger from the alternator.

So does this setup sound like a decent start?

200 Amp or 400 Amp model? I can't for the life of me understand in this day and age using Edison era technology. A resistive current shunt in a high efficiency battery bank is like going on a diet and eating nothing but cake. ice cream, and pizza. There are drop in hall effect current sensors that will replace that shunt. It eliminates two electrical connections that can fail. The shunt itself during high amperage consumption waste energy via heat.

 

[LeishaShannon]

Just do it... you won't regret it.

They're lighter, stronger (support higher loads, faster charging), and cheaper per Ah delivered.
The benefit of being able to charge at ridiculously fast rates has been invaluable, a nice drive or fast idle charging via the alternator and you're set for another few days even if the solar is ********.
No "tail" on charging current means you're not wasting a single ray of solar or drop of fuel if you're using a generator/engine to charge.

We're coming up to almost 4 years full time travel in a totally lithium powered camper (air con, induction hotplates, oven, microwave, breadmaker, etc)
No per cell monitoring, no balancing, no BMS, and the cells are still within 50mv when full and the output of the pack is 100% of rated capacity (it was initially 104% or so)
For the first 12 months or so I had anal cell monitoring, LVC, HVC, etc etc but over time discovered it was just not required and I felt it posed higher risk than reward.
We now simply use the BMV-702's midpoint monitoring and periodic (someone messaged me recently which reminded me to check, prior to that my last check was over 12 months ago, Oops!) cell voltage checks using a celllog8.

If you're not confident to DIY, find a company/consultant you trust to assist with the design and to have on call with any questions. A -lot- of people over complicate things because of this perceived need to protect the "expensive" cells. its BS in my opinion.

( YMMV, this is just 1 camper's observations, and is worth what you paid for it. )

 

[VerMonsterRV]

A resistive current shunt in a high efficiency battery bank is like going on a diet and eating nothing but cake. ice cream, and pizza. There are drop in hall effect current sensors that will replace that shunt. It eliminates two electrical connections that can fail. The shunt itself during high amperage consumption waste energy via heat.

I have read a bit about the hall effect sensors and some places say they are not as reliable over the long term as a shunt (I have a 18 year old one on the boat that is still working fine). Would you know if this is true or not and if not point me towards a BMS that uses a hall effect sensor?

I was planning on the 200 amp version as I do not foresee ever coming close with a 200 amp charge or load. Though the 400 is only a few bucks more and would give much more head room.

No per cell monitoring, no balancing, no BMS, and the cells are still within 50mv when full and the output of the pack is 100% of rated capacity (it was initially 104% or so)
For the first 12 months or so I had anal cell monitoring, LVC, HVC, etc etc but over time discovered it was just not required and I felt it posed higher risk than reward.
We now simply use the BMV-702's midpoint monitoring and periodic (someone messaged me recently which reminded me to check, prior to that my last check was over 12 months ago, Oops!) cell voltage checks using a celllog8.

I have heard of people doing just this same thing, not sure if I am brave enough at this point though. When you mention you thought it posed a higher risk, is it because of more parts and connections?

 

[LeishaShannon]

I have heard of people doing just this same thing, not sure if I am brave enough at this point though. When you mention you thought it posed a higher risk, is it because of more parts and connections?

Exactly, I have fused 2.5mm2 (from memory) cables to each cell which terminate to powerlab8 and celllog8 connectors for easy connection if/when required for voltage checks or balancing. Nothing permanently connected.

 

[CoyoteThistle]

I agree generally with LeishaShannon on all he says. On the other hand though, there is comfort in having a BMS if something in the system goes haywire.

That being said, I'm not crazy about that BMS kit from ECPC but I bet it will work okay. A better design would protect the battery at the cell level, not just pack level (i.e., BMS triggered if any cell reaches 3.65v versus pack at 14.6v or cell at 2.5v versus pack at 10v). If the balancer doohickey fails (probably unlikely) and cells get out of balance, you can damage a cell even when the pack voltage is within the safe zone. Probably safer to do a careful initial balance and then remove the balancer - one less thing to fail, and as LS says, if you are charging right, cells will stay in balance.

Keep in mind also that that BMS is basically your "oh s#%t" battery protection. If the low voltage relay triggers, everything will be shut down. Consider adding something like a Victron Battery Protect that will disconnect most loads at a slightly higher voltage and warn you of trouble before you get shut down completely. I use the BMV-702 as well for warning level voltages. These just offer some cheap insurance/redundancy.

Another thing I would recommend is going higher quality on the solenoids. Those ECPC ones draw 1.5 Ah when energized - that kind of draw adds up, especially on the low voltage disconnect one (to loads, normally open). It will be energized basically all the time - that's 36 amps or so a day. Something like the Blue Sea L-Series draws about 0.1 Ah when closed IIRC.

 

[dreadlocks]

I'm using my BMV-712 and a Battery Protect LVD (solid state relay, very low power needs) for a tunable primary BMS on my Battle Born, recently set it up so all load/charge is on the same side of the BP and I monitor the load side as a "starter" battery w/the 712's dual battery feature.. the BMV relay output controls the Battery protect and when calculated SOC gets too low it disconnects the battery, when battery voltage gets too high (14.2v) it disconnects and stays disconnected until its removed from shore power because its monitoring the load side too and wont reconnect til both drop below there set points.

have an parallel manual switch (labeled reserve power) with the BMV that over-rides and reconnects the Battery Protect, BMV is set to disconnect at 20% SOC left and if I want I can flip the switch and get another ~15% out of the battery before it drops below 12v and the battery protect's internal programming overides my override at about 5% SOC, still before the BB BMS disconnects loads.. the reserve switch is also used to re-connect the battery to the charger if its in a low SOC state and is intended to be used sparingly, but easily (heater shuts down in middle of night)

Testing out this new config in a dry run now and it seems to be working well..

 

[luthj]

I would be wary of buying cells sight unseen. They could have widely different ages or different production batches. Ideally the cells should be from the same production batch, and read within 0.01 volts of each other.

 

[VerMonsterRV]

I would be wary of buying cells sight unseen. They could have widely different ages or different production batches. Ideally the cells should be from the same production batch, and read within 0.01 volts of each other.

Thanks for this reminder, I have asked for the batteries to all be from the same manufacture date (they all have a serial number with the first few digits being the manufacture date. I had asked for consecutive serial numbers but from the serial numbers they sent me they make at least a thousand on manufacturing days.

 

[VerMonsterRV]

Hey guys, been doing a bit more reading and thinking about the suggestions made here. I have made the request from the battery supplier to send me the invoice so I can move forward with the order (16 100Ah 3.2 aluminum cased cells for a 4p4s bank at 400Ah at 12v). I have also stumbled on Thornwave Labs and his BMS/solid state relays. I really like his approach to the BMS (no screen, all configuration and monitoring via an Android/iOS app by bluetooth). The BMS comes with a built in 60 amp shunt but I will likely use a larger external one as the 60 amp is a bit small. He will soon have (a few weeks out, they are new) 100 amp solid state relays that fit in a standard ANL fuse block for mounting.

 

[Hillbilly Heaven]

I do like the headless design. I have been looking for a wireless monitor device.

 

[Hillbilly Heaven]

Sat down and read the manual for the Thornwave Labs Bluetooth battery monitor. It appears you can select different shunt voltages which is good if you want to use something besides the Edison energy wasting resistive type current shunts. I think those that have seen my post know I am very much anti current shunts. Thornwave gives you the option to select anyone of these as the current sense voltage when using an external shunt, + 7.5mV, + 15mV +30mV + 60mV, +80mV. He recommends selecting one higher than the expected shunt voltage. I guess that is the reason for the 60mv and 80mv as typical current shunts can be either 50mV or 75mV. I recommend reading the manual closely especially the example on page 14 as you must also calculate the shunt resistance. Shunt Voltage and Shunt Resistance are important in measuring the correct current.

To eliminate the waste of energy from the resistive current shunt I recommend you use a Hall Effect current sensor which is electronic in nature and only consumes 8.1mAmps of current and it is not damaged in over current conditions.
These will fulfill your needs for current monitoring. Use the ones with the + 50mV output and select + 60mV on the Thornwave. There is some discrepancy in the documentation as to the current ranges available website says 100,200,300 amps and the data sheet says 100-600 amps in hundreds. Model number should be DCS30-XXX-1 where XXX is the amp rating.

http://www.inpowerdirect.com/dccurrentsensors_halleffectsensors.php

Data Sheet:
http://www.inpowerdirect.com/docs/PDS-162A.pdf

 

[Hillbilly Heaven]

I don't usually post links from Evil Bay but for less than $35.00 you can purchase the 300 Amp version of the one I posted.
https://www.ebay.com/itm/InPower-Model-DSC30-300-1-DC-Current-Sensor-300-Amp-/302771756837

 

[VerMonsterRV]

I just contacted Thornwave about using the sensor on your link. I am all for fewer connections if it increases reliability. My battery bank is now on order and I am awaiting the pack test results and shipping information.

 

[Rando]

It would be wise to do some analysis on "Edison energy wasting resistive type current shunts" before switching to a hall effect sensor. In a normal usage scenario the hall effect sensor will waste far more energy than a shunt, but neither will waste even close to enough energy to worry about.

According to the spec sheet for the hall effect sensor above it requires ~8mA at 12v supply voltage - which is 2.3Wh per day, regardless of load.

Now consider a standard 500A/50mV resistive shunt. If you were to average a 10A current draw 24 hours a day, your shunt would consume 0.24Wh per day. You would have to be averaging more than a 30A draw, 24 hour a day for the shunt to waste more power than than the hall effect. But in either case it is completely insignificant amount of power.

There maybe other good reasons to switch to a hall effect current sensor - but energy wasting is not one of them.

 

[VerMonsterRV]

Some more good info, I forwarded the link to the hall effect sensor to Thornwave and he is planning on ordering one to test. He did point out the energy usage. Even more important to me is the accuracy, Razvan from Thornwave said the shunts are more accurate (still might go with a shunt as I already own one and if they are more accurate then all the better). Maybe once he gets his, he can confirm.

I just got the test results for my battery pack from the manufacturer. I attached it if anyone is interested. I am not a battery (or electronics expert) but the batteries all tested to about 10% over capacity. I think this is fairly normal from my reading on the web. Batteries are scheduled to arrive next Monday via FedEx.