Free 7 Day Trial RV GPS App RV Trip Planner Campground Reviews RV Maintenance Free 7 Day Trial ×
 


Reply
 
Thread Tools Display Modes
 
Old 05-27-2021, 02:28 PM   #1
Senior Member
 
Join Date: May 2018
Location: Arizona
Posts: 197
DIY LiFePO4 100 Amp-Hr battery Build

I know there will probably be some interest in this once people see what it is. I have been somewhat reluctant to dig into this myself but now that I priced out a 100 Amp-hour configuration it is just not worth doing lead-acid deep cells.

There is even more reason for me to look at this now because I have two frame-mounted OEM battery boxes and LA maintenance is not something I'm looking forward to.

While Will Prowse's is recommending $280 Amp=-Hr configurations, 100 amp-hour works much better for my dual battery box configuration. With the variety of BMSs available, there is a corresponding variety of battery configurations also possible.



I have linked a couple of YouTubers that have been reviewing the cell and BMS manufacturers and purchasing off Ali-Express so I don't think this is really uncharted territory.

https://www.sportsmobileforum.com/fo...tml#post296405

I initially had some concern about mounting Lithium batteries under the cab where it is not environmentally friendly. However, with a thermostatically controlled heater pad for freezing conditions and some thermostatically controlled fan for the other extreme, I think this provides a very simple, cheap and workable solution.

I will probably use some type of PVC enclosure although it will not be fully sealed. It will also fit within the factor battery boxes to avoid and direct water spray.

In the attached figures you can see the conceptual design. I just ordered the parts from Ali-Express so not sure how long that will take. The cells are guaranteed to be delivered by Aug 6th but the order says they are ready to ship so we will have to see.

Here is a list of the parts in the BOM with links. Excluding an enclosure, wires, and connectors, the total cost is coming in at $529 for two 100 Amp-hr batteries or $265 per unit. (includes a spare heater pad as well)

I'll update as the parts come in and as soon as I'm able to do any testing.

VariCore LiFePO4 100 Amp-hr 3.2V Cells
https://www.aliexpress.com/item/4001...73224c4drGX5C8

Daly Smart BMS 60A 4S
https://www.aliexpress.com/item/1005...77154c4dyPmty5

Facon 3 '' x 13 '' Elbow Tube Heater Pad
https://www.amazon.com/gp/product/B0...A16G53YHOQFM2H

uxcell KSD9700 Thermostat, Normally Open 40C Temperature Switch
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

19mm Silent 12V 0.08A 5010 5012 DC Brushless Quiet Fan
https://www.amazon.com/-/es/gp/produ...0NZWY05K&psc=1
Attached Thumbnails
Layout.jpg   BMS.jpg   BOM.jpg  
__________________

posplayr is offline   Reply With Quote
Old 05-28-2021, 09:14 AM   #2
Senior Member
 
Join Date: Jul 2016
Location: Seattle, WA
Posts: 343
Looking forward to watching how this comes together.
__________________

Nrobert10 is offline   Reply With Quote
Old 05-28-2021, 10:06 AM   #3
Member
 
Join Date: Jan 2020
Posts: 49
Quote:
Originally Posted by Nrobert10 View Post
Looking forward to watching how this comes together.
Me too looks promising
bisonthecruiser is offline   Reply With Quote
Old 05-30-2021, 10:14 PM   #4
Junior Member
 
Join Date: Nov 2020
Posts: 19
I would probably add some active balancers into the mix if you plan on charging at high amps, you can never allow the battery to go out of balance at the high end and activate the bms to shut down the charging. Also if the battery compartment gets too hot that might trigger the bms to activate.

With the mosfet based bms, if it activates that could be bad. With solar it creates voltage surges, I'm not sure what would happen while charging with an alternator. I wouldnt want to find out and would try to avoid the situation since modern vehicules have alot of components that are sensitive to voltage spikes.

I learned from trial and error what the worst case scenario that can happen when the bms activates. I learned the hard way that alot of 12 devices won't survive the voltage surges.

I'm been using the chargery bms8t (mechanical relays to stop the charging) to avoid the voltage surges.

Active balancers I been using. These cost about 100 dollars for 4s model. It peaks at 6 amps of balancing current as opposed to the 60ma balancing current of most bms.
Attached Thumbnails
active balancers.jpg  
jonyjoe101 is offline   Reply With Quote
Old 05-31-2021, 03:11 AM   #5
Senior Member
 
Join Date: May 2018
Location: Arizona
Posts: 197
Quote:
Originally Posted by jonyjoe101 View Post
I would probably add some active balancers into the mix if you plan on charging at high amps, you can never allow the battery to go out of balance at the high end and activate the bms to shut down the charging. Also if the battery compartment gets too hot that might trigger the bms to activate.
Yes I had decided the same. The Daly BMS only has 30mA of balance current which compared to 100 amp-hr cells is not much. The "Cheaper than AGM" guy used this one and the reviews seem generally very good. I debated about just; leaving the connector hanging so that it would allow for a periodic maintenance balance but seems like just leaving it in is not going to hurt anything.

https://www.aliexpress.com/item/4001...40534c4d2ucuHy

Quote:
Originally Posted by jonyjoe101 View Post
With the mosfet based bms, if it activates that could be bad. With solar it creates voltage surges, I'm not sure what would happen while charging with an alternator. I wouldnt want to find out and would try to avoid the situation since modern vehicules have alot of components that are sensitive to voltage spikes.
I think what you are describing is called "load dump" and it is primarily from disconnecting alternators. Yes I also saw a rant from a german guy that talking about how little protection the Daly BMS's have. Generally, with lead-acid you do not need to protect anything that is directly across the battery because you simply can raise the battery voltage up tens of volts. That said I have a simple scheme to add some high power TVS's right across the battery terminals

https://en.wikipedia.org/wiki/Transi...age_suppressor

Quote:
Originally Posted by jonyjoe101 View Post
I learned from trial and error what the worst case scenario that can happen when the bms activates. I learned the hard way that alot of 12 devices won't survive the voltage surges.
It sounds like the BMS is to be treated like a fail-safe rather than an active control component. When it disconnects that is going to be a large load dump especially for any attached inductive devices (e.g. motors/pumps)

So TVS protection at the battery terminals might protects anything both inside the battery and any loads outside.

What did you knock out if you don't mind saying?

Quote:
Originally Posted by jonyjoe101 View Post
I'm been using the chargery bms8t (mechanical relays to stop the charging) to avoid the voltage surges.

Active balancers I been using. These cost about 100 dollars for 4s model. It peaks at 6 amps of balancing current as opposed to the 60ma balancing current of most bms.
The Chargery is designed for electric vehicles. You were probably learning about Back-EMF LOL. Are you using it on an EV?

A "motor" can act as a motor when you apply current to it which means electrical power in and mechanical power out. But it also works in the opposite direction when it turns into a "generator". Even if you do not disconnect but have regenerative braking for example the terminal voltage of the motor will exceed the battery and the motor while try and stuff a bunch of current into the battery. With lead-acid the internal resistance limits this somewhat, but with lithium there is much lower impedance so the spikes will be larger.

charger model power, specially design the equalizer, smart balancer and lipo balancer for R/C model

As far as a mechanical relay, that is not a lot better than a FET as far as a creating load dump. If there is inductance (there is always some especially with motors or long wire leads) then there is a voltage spike associated with interrupting current.

Nowadays you don't really design with a simple FET. there are things called Smart FET that have the associated protections built right into the device. Then there are more highly integrated parts like High Side switches and I'm fining some battery management parts but really long lead times and minimum buys.

https://www.st.com/en/power-manageme...tml#sample-buy


I have some simple TVS devices from previous projects I think I can make work for at least some protection.
posplayr is offline   Reply With Quote
Old 05-31-2021, 01:32 PM   #6
Junior Member
 
Join Date: Nov 2020
Posts: 19
The problem with the mosfets is they leak voltage and the battery will read about 11.7 volts when the bms activates. Some chargers seeing a "low" battery will try to force a charge into the battery and since the bms won't allow charging you might get voltage surges. I lost 12 volt fans/pumps and led lights that couldnt handle the surges (while charging with solar).

I tried using a overvoltage protection relay to protect my devices but they operate to slow prevent damage. One thing that does work is connecting all 12 volt devices to a 12 volt voltage stabilizer.
I'm using the chargery on my 4s 220ah lifepo4 batterybank, I havent lost any devices since I installed this bms 2 years ago.

The problem with a mosfet bms activating is that it remains activated until manually reset. While its activated whatever is trying to charge it will keep cycling back and force trying to force a charge on the battery. The TVS has to be able to handle that constantly. With a mechanical relay, the battery will be out of the loop once the bms activates.

In my situation I only charge my lifepo4 with solar, so with the alternator might be different results. But since you mention a load dump, you will be ok if charging with the alternator only, since when the bms activates there shouldnt be any surges since the 12 volt lead acid start battery will still be accepting the alternator output, you might not even need the TVS.
jonyjoe101 is offline   Reply With Quote
Old 05-31-2021, 04:35 PM   #7
Senior Member
 
Join Date: May 2018
Location: Arizona
Posts: 197
Quote:
Originally Posted by jonyjoe101 View Post
The problem with the mosfets is they leak voltage and the battery will read about 11.7 volts when the bms activates. Some chargers seeing a "low" battery will try to force a charge into the battery and since the bms won't allow charging you might get voltage surges. I lost 12 volt fans/pumps and led lights that couldnt handle the surges (while charging with solar).
I think you are describing a situation where the BMS is disconnected (i.e. a series MOSFET is OFF) but still showing some terminal voltage. The MOSFET is a very high impedance when OFF. It is as if it is not there. If there is a voltage it must becoming from a solar controller or somewhere else.

If the BMS is sensing the terminal voltage of the battery that might be applying a voltage. I'm guessing somewhat as I'm not that clear on what the topology is of a BMS. My assumption is that is sensing the individual cells and if something is outside the limits it disconnects with a series MOSFET. I guess it also has some small equalization currents it can apply but dor the Daly that is only 30 mA.

This is another reason to improve the logic in the DC-DC charger. The Renogy describes something it calls "Lithium Activation" for starting a BMS disconnected battery.


Quote:
Originally Posted by jonyjoe101 View Post
I tried using a overvoltage protection relay to protect my devices but they operate to slow prevent damage. One thing that does work is connecting all 12 volt devices to a 12 volt voltage stabilizer.
I'm using the chargery on my 4s 220ah lifepo4 batterybank, I havent lost any devices since I installed this bms 2 years ago.

That is good to know. I have now ordered $200 in BMS/Active balancers and whatever solution I choose it is multiplied by 2 because of my two separate batteries.

I'm not looking forward to changing my BMS but it is good to know there are fallbacks.

Quote:
Originally Posted by jonyjoe101 View Post
The problem with a mosfet bms activating is that it remains activated until manually reset. While its activated whatever is trying to charge it will keep cycling back and force trying to force a charge on the battery. The TVS has to be able to handle that constantly. With a mechanical relay, the battery will be out of the loop once the bms activates.
As noted above, your BMS should never disconnect. I have the Rich Solar 40Amp controller with separate solar, Battery, and Load terminals. If the batteries get low the solar controlled should disconnect the load way before the BMS disconnects. Basically, you need to watch the batteries and make sure that either through loads or self-discharge the LiFePO4 packs do not trigger their respective BMSs to disconnect. If you are going into long-term storage where there is the possibility of draining the batteries, then I would disconnect the solar ( I have a 15 amp disconnect).

So basically I do not understand the rationale of having a mechanical relay disconnect. Is this between the LiFeLP4 and the solar charge controller?

I have this 120V 10A charger. It seems to be pretty stable when I charge a lead-acid battery. And it does seem to shut down but it is a lead-acid battery charger. Maybe I need to rethink that as a long-term charger.

Quote:
Originally Posted by jonyjoe101 View Post
In my situation I only charge my lifepo4 with solar, so with the alternator might be different results. But since you mention a load dump, you will be ok if charging with the alternator only, since when the bms activates there shouldnt be any surges since the 12 volt lead acid start battery will still be accepting the alternator output, you might not even need the TVS.
[/QUOTE]

So if you are only charging with solar, what happens to your solar controller when there is a BMS initiated battery disconnect??

Load dump is generally related to anything inductive where you disconnect the load (i.e. V=L di/dt). This is primarily the alternator but could also be a motor or possibly long leads to a battery that is disconnected. The voltage specs are like +/- 100 volts. Generally, any series resistance helps limit the current spikes. With Lithium, there is much less battery internal resistance. The hardest thing to protect is surges at low impedance power terminals. So Lithium is among the worst.

One thing that I have come much more aware of is the danger of a BMS disconnecting a battery from a solar charger with a high solar panel input. With the disconnected battery input, almost all of the solar controllers say DO NOT DO THIS! Because of this, I'm setting g all of my LiFePO4 battery fusing based on a catastrophic failure level (way above active control limits).

I just came up with another problem scenario.
For example, the solar charge controller should only push 25 amp for my 350-watt panel to the battery. I will also have a 10 amp 120 VAC shore power charger. The Renogy will be capable of 40 amps so this is 75 amps maximum. If I disconnect the battery because of the over current I will blow the solar controller. This is an unlikely scenario but it is possible if I am sitting outside, onshore power, and start the engine.

OK I just decided I need to look at the house battery voltage before deciding to push 40 amps into it based on alternator voltage.



So I searched for "voltage stabilizer' and found these. They all seem to be DC to DC converters. The active power supply control is going to be in the low kHz range. If there is any capacitance then DC to DC will do something so I can not know how to quantify the difference between a "stabilizer' DC-to-DC to the other plain DC-to-DC converters. I have a 20 amp breaker on my DC loads (excluding invertor) so I could pair up a couple of the 10 amp DC-to-DC units for $40. I don't know how to compare that to spending $100 for two of the official "stabilizers".

Secondly, you have to ask what is this doing that the Rich solar controller is not doing? (The Rich has separate load terminals) If a spike is coming down the battery terminals does it just propagate through the solar controller and into the load? If so what is the point of the separate load terminals? The solar controller will try and keep the battery terminals stabilized depending upon the charge mode. So I'm not sure what the difference would be. Now if you did not have separate load terminals then yet the stabilized will isolate battery/charger junk from the loads.

So enough guessing, I drew up what is a likely solar charge controller topology where there are separate terminals for each collar, battery, and loads.



https://www.amazon.com/-/es/gp/produ...2L3PSG09&psc=1

https://www.amazon.com/dp/B082GD23W3...2s9dHJ1ZQ&th=1

I think the HSS (e.g. VNQ660SP) will go a long way to remove transient if not stabilize like a DC to DC convertor. It is not a DC to DC so it cant do a voltage translation like Buck-Boost. But what it does is active controls the gate on the MOSFET to limit current or open the circuit completely in the case of overcurrent/thermal. That little PowerISO-10 will provide 10 am per 4 channels. You have to keep it cool but it works very well.

I designed this product as a sorta hobby, sorta see what it takes to produce a commercial product. It worked very well and is primarily possible because of the VNQ660 type tech .

You can see it is pretty fast with turn-on and turn-off slopes of 300-400 Volts/mSec. That means a 10-volt swing happens in 0.03 mSec This is approaching 15 Khz but doesn't even consider the transient surge suppression. It also has real transit performance with respect to load dump (see Table 12). It doesn't regulate but does real well with junk!

I will have to heat sink them but will probably fabricate a small device to pass the power leads through. i plan to make something for some bulkhead connectors on the battery box.

These devices are just a smart FET with additional functions so once they are ON they are bidirectional. I don't think it will matter if a battery is charging or discharging.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1


https://www.thegsresources.com/_foru...State+Powerbox
Attached Thumbnails
VoltageStabilization.png  
posplayr is offline   Reply With Quote
Old 06-09-2021, 10:28 PM   #8
Senior Member
 
Join Date: May 2018
Location: Arizona
Posts: 197
A quick update. The battery cells, BMS, and equalizers have all been shipped and are at least in the LAX customs process. I should see them all by early next week. The equalizers were ordered May 28, and the other two on the 27th. This is going much faster than the originally quoted August 8th dates.

The battery configuration has changed and I have also ordered the Overkill Solar 4S/ 125A BMS and it shipped today. Basically, the frame-mounted batteries just do not work with the much higher currents of the Lithium batteries. The main components are just too far from the LiFePO4 batteries and then there are the environmental issues for the batteries and trying to weather waterproof the DIY open cells and BMS under the vehicle.

So now I'm now going to build one 200 Amp-Hr battery in a large commercial battery box (it will be cut down to 19" in length and the ABS rewelded). This is having a major ripple effect in my previous plans.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1


I'm currently working on a surge/load dump-protected bus bar for the front of the battery box. The box will go in a cabinet where it is close to the
Rich 40A solar charger
https://richsolar.com/products/40-am...rge-controller

600W Pure Sinewave invertor.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Renogy 40A DC-DC Charger.
https://www.amazon.com/Renogy-Batter...a-802511223837
Attached Thumbnails
ShippingStatus_2021June9.jpg  
posplayr is offline   Reply With Quote
Old 07-31-2021, 09:38 PM   #9
Senior Member
 
Join Date: May 2018
Location: Arizona
Posts: 197
I received my LifePO4 Batteries from AliExpress. I have done some calibrations and testing of the battery pack in a 4S configuration using two 100Amp-Hr cells in parallel for each 1S.

Other than over-stressing my equipment, I think I have a good battery pack (except for the Class B case swelling).

https://diysolarforum.com/threads/pa...ocedure.26301/
posplayr is offline   Reply With Quote
Old 08-22-2021, 03:23 PM   #10
Senior Member
 
Join Date: May 2018
Location: Arizona
Posts: 197
I'm still negotiating with the seller for the bloated Qty 8 100 Amp-hr cells I received. Of course, this seems to be about as productive as speaking to a fence post.

We are also looking at a battery backup system. Based on many glowing reports and endorsements at the DIY Solar Forum, Amy Wan is the most trusted source of grade A matched cells that they buy direct from the manufacturer EVE.

https://diysolarforum.com/threads/or...-luyuan.25236/

They are purchased on Alibaba (a Chinese version of B2B Amazon) and not from Aliexpress (a Chinese equivalent of a bad eBay).

https://www.alibaba.com/product-deta...9d082fc2t76hbE

The cost for Qty 32 grade A, new (as of early Aug 2021) product matched cells was $126 per cell plus $711 shipping and another $140 for the credit card fee using AMX. You don't want to wire the money and then try and claw that money back if something goes wrong without a CC company on your side.
__________________

posplayr is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Powered by vBadvanced CMPS v3.2.3
Disclaimer:

This website is not affiliated with or endorsed by Sportsmobile SIP or any of its affiliates. This is an independent, unofficial site.


All times are GMT -6. The time now is 04:54 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
×