Victron Battery Monitor alternatives & lifepo4 questions

hour

hour

Observer
If you have a rather predictable load (solar keeping battery system floating all day, fridge the only draw in the evening) could one just buy an ammeter battery monitor for 1/10th the price? I figure the worst my setup will see is an uncharacteristically warm evening @ 10,000 ft, and a lot of drinking after sundown. If I get through one of those nights and find my capacity is fine the next morning before solar starts producing, I wouldn't really care to monitor the state of things too often. Certainly not enough to warrant a $150-200+ battery monitor.

Second, I just committed to a lifepo4 setup to run my fridge and charge USB devices during the day. Here's what I have so far...

- Victron 75/15 charge controller (connected to the soon-to-be-replaced 110ah failed deep cycle)

Just bought:
  • 4 x 3.2v K2 Energy 90AH Lifepo4 cells
  • Victron BatteryProtect Smart-65 amp (with the new bluetooth ability, and 65a because I know I'll never exceed that...)
  • ISDT 300w/14A smart battery charger/discharger/balancer
  • A harness to make balancing leads that plug in to the ISDT unit

Following this seemingly smart kid's guide, here's what I plan to do when I receive the above.

  1. Test voltage of each cell.
  2. Hopefully discover in step 1 that they're close enough to be paralleled to one another and left to equalize that way
  3. Once equalized, wire them up in series
  4. Connect balancing leads to cells and then hook up battery charger/discharger/balancer
  5. Run inverter or some significant load to drain the battery down to resting voltage of around ~3v per cell, monitoring each cell during
  6. Bottom balance the cells
  7. Charge them up to full

I have no BMS, and the guy in the video seems to think that's okay because the cells shouldn't be coming out of balance in a "low C solar application". Does that sound right? If not, I can get a 4S lifepo4 BMS of suitable amperage. If YES to BMS, since the connector will be the same (5 pin) to the BMS and the charger/discharger/balancer, is it appropriate to swap the harness from the BMS to the charger, or should there be a dedicated harness and keep the BMS hooked up permanently?

I'll be running this system in my living room for a week or two to get comfortable with things and observe individual cell voltage as the pack charges and discharges. I intend to hook up the Victron BatteryProtect with a rather high cutoff during this time to play it safe.

Does this sound like an appropriate plan?

Also, the ISDT 300w/14A charger/discharger/balancer accepts DC input of 7-32v, 15A max. If I return home from camping and my solar setup has blown off on the highway, I suppose that means I could connect a dumb DC power supply to it and top things off. But that also has me wondering about powering from the car, skipping the Redarc dc to dc smart charger or any isolator setup (do not own, would prefer not buy).

The only time I've ever needed charge from my alternator for my existing setup is when heading to camp. panels shadowed by stuff on the roof rack, and fridge chugging away. Since everything is floating and full up until I shadow a panel, that means I have a few hours of drive time where the fridge is cycling and I'm consuming a bit more than I'm putting back in. Charging at even 30w would basically make this all a null issue. So how about an ignition triggered relay and 10 gauge wiring to the truck bed with an XT60 connector that I can plug directly in to charger/discharger/balancer, and set the max charge current to 5 amps. More than enough to cover what's being used for the fridge and easy on the wiring. While I understand this isn't a plan with growth in mind, is it a sound plan?

If anyone made it to the bottom of this, thank you. It's 6:30am, not a wink of sleep, work in 2 hours, but tonight I succumbed to the lifepo4 itch.
 
J

jonyjoe101

Adventurer
Without a bms I would definitely get some active balancers (100 dollars) and an overvoltage protection relay(6 dollars). I found out lifepo4 cells go out of balance when fast charging, even when slow charging near the top end they go out of balance. The 4s active balancers I use balance all the time while charging/discharging, they can balance at up to 6 amps constant, so they are capable of keeping up with fast charging. I use different brands of lifepo4 and they all gave me balance problems near the top end. If you plan on only using a balance charger everytime on your 90 ah lifepo4, after a while it will become inconvenient. Even on my small 27ah li-ion pack I just plug it into my solar to charge it and let the bms/overvoltage relay control the charging, I can also plug into my cigarette lighter and charge it that way. The active balancers are expensive but its the best money I ever spent, I had them a year connected 24/7 to my battery and havent had any more balance problems.

When you install the 4s connectors, it doesnt hurt to add extra 4s connectors, both male and female ends if you got them. I sometimes connect LCD voltage monitors, low/hi voltage alarms, bms, active balancers. With expensive lifepo4 you want to know their status all the time.

You do need a coulombmeter, but no need to spend hundreds, you can get a "DROK LCD Digital Multimeter Charge-Discharge Battery Coulometer Tester" on amazon for less then 30 dollars, I use it on my 4s 220 ah lifepo4. It can handle up to 75 amps in/out . The lifepo4 battery resting voltage is about 13.1 volts between 10 and 90 percent, so you won't be able to tell its status unless you keep track of the amps you use. The drok counts amps in/out and gives you a percentage of what the battery has available.

I have one of the 14 amp isdt q6 chargers, though they have large input voltage range, they need a stable power source (wall power or other battery). If the input voltage fluctuates a little it shuts down. I see the programming of the charger everytime I need it to be a hassle. I only use it when I build a new battery pack. I charge my battery directly from solar and let the bms, overvoltage relay, and active balancers shutoff when charged. If the battery has balance issues, even with the isdt, it can take hours to charge, once a cell goes out of balance the charge drops to 1 amp. Its a good charger for smaller packs but I wouldn't use it everyday to charge a pack larger then 10 amps.

active balancers
508535


drok coulombmeter
508536
 
hour

hour

Observer
Yikes, not exactly what I wanted to hear but good to know. What is considered fast charging for your bank? I'll be charging with the Victron 75/15 on the lifepo4 profile-200w solar. I only intended to use the monitor/charger/discharger in the beginning like you say, then periodically to check things. I was questioning the possibility of powering the unit from my starter battery for say 4 hour drives where the panels are shaded from roof cargo just to make up for what the fridge is using during that time getting to camp. Based on what you said it might conk out as my smart alternator does..smart things.

Curious why that Prowse guy in the video seems so convinced that what he built will remain so well balanced, due in part to being solar charged. I think he had a 40 amp controller hooked up to it and over 1,000w solar. I'll sit at about 10 amps in from solar (24v system).

Could have sworn things like these DROK ammeters were preferred over coulometer types from youtube builds / jehugarcia maybe.. Not sure how I'll go about testing the capacity of the battery once complete so that I can calibrate anything.

Thanks a bunch
 
Last edited:
hour

hour

Observer
richxd87 said:
@jonyjoe101 wow that "DROK Coulometer" looks just like the Expion360 Battery Monitor that goes for $199.

I currently have FLA batteries in the camper right now but plan to upgrade to LFP in the future. Is the Drok compatible with both battery types?

https://www.expion360.com/universalbatterymonitor
https://www.ebay.com/itm/DROK-LCD-D...123651773117?_trksid=p2385738.m4383.l4275.c10
Click to expand...

I don't think these shunt based capacity meters care about your battery chemistry. You input your battery capacity, and they know what goes in and out of the battery via the shunt- allowing a gauge to be displayed. Here's an affordable capacity gauge and here's a video of it being evaluated on a lithium pack..
 
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