2 lithiums instead of 1? SOK batteries?

kent_island_sailor

Super Anarchist
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Kent Island!
I am getting my list together for a cheap-ish lithium setup. One concern is with a BMS opening up at an inopportune time and going dark-ship while transporting orphans through a minefield or maybe having all the beer get warm.
So maybe this is too simple to work, but wouldn't 2 100AH batteries alleviate that risk. The only reason I can see for both to cut off at once is if there is a good reason like going dead or overheating. Other than that, a random failure would just take out 1 of the 2.
I also discovered the SOK brand batteries have easily opened cases, so if the BMS did crap out it could be replaced or bypassed if need be pretty easily. That seems to beat most of them that would need sawzall surgery!
 

efrank

Member
294
133
I will be interested to see what you come up with. SOK batteries come in metal cases and plastic cases (what they call marine grade). A quick search didn't show a 100 AH in a plastic box.
 

penumbra

Member
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WLIS (ish)
There's a school of thought that you should keep a lead acid or AGM in the mix to be a buffer. I don't remember the details, but Clark of Emily and Clark had a kooky, but clear explanation as I recall. I've seen mentions of "surge suppressors" for this, but damned if I've found one.

If you're going with any of the other common DIY brands (Battleborn, Dakota, etc.), I suspect they can give you some wisdom.

Does seem like a real risk of the drop-ins that is not often covered by the usual YouTube stars and DIY articles.
 

kent_island_sailor

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There's a school of thought that you should keep a lead acid or AGM in the mix to be a buffer. I don't remember the details, but Clark of Emily and Clark had a kooky, but clear explanation as I recall. I've seen mentions of "surge suppressors" for this, but damned if I've found one.

If you're going with any of the other common DIY brands (Battleborn, Dakota, etc.), I suspect they can give you some wisdom.

Does seem like a real risk of the drop-ins that is not often covered by the usual YouTube stars and DIY articles.
My system is going to be Alternator > AGM start battery > DC-DC charger > Lithium house battery.
The DC-DC charger handles the charge profile for the lithium and the alternator doesn't see it directly.
 

eliboat

Super Anarchist
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I feel like it’s worth a couple of extra bucks to build your own battery with a solid BMS that you have control over and that doesn’t limit you with regards to charging and discharging, as you are now opening a contactor instead of a mosfet. Obviously you want to stay within the limits of the cells that you’re working with, but you will always get a better system this way. Your proposed setup would build in some redundancy, however I will say that if you’re not doing anything extreme with regards to charging/discharging, your batteries will happily deliver. The weak point on most of the cheap drop ins is the BMS, after that, many have questionable construction. I think the SOKs are OK iirc, but it’s easy enough to check by watching one of Will Prowse’s tear downs on YouTube, which I assume you already have.
 

kent_island_sailor

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I feel like it’s worth a couple of extra bucks to build your own battery with a solid BMS that you have control over and that doesn’t limit you with regards to charging and discharging, as you are now opening a contactor instead of a mosfet. Obviously you want to stay within the limits of the cells that you’re working with, but you will always get a better system this way. Your proposed setup would build in some redundancy, however I will say that if you’re not doing anything extreme with regards to charging/discharging, your batteries will happily deliver. The weak point on most of the cheap drop ins is the BMS, after that, many have questionable construction. I think the SOKs are OK iirc, but it’s easy enough to check by watching one of Will Prowse’s tear downs on YouTube, which I assume you already have.
That is a whole next level of cash to do it that way. The fun thing with the SOK batteries is you can open the lid and swap out the BMS if you get the urge, it is not sealed in there.
Between the two batteries I'll have 100 amps charge and 200 amps discharge, which in both cases is about twice what they will ever see.
 

Brawr

New member
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New Zealand
That is a whole next level of cash to do it that way. The fun thing with the SOK batteries is you can open the lid and swap out the BMS if you get the urge, it is not sealed in there.
Between the two batteries I'll have 100 amps charge and 200 amps discharge, which in both cases is about twice what they will ever see.
That's just answered the only point I was going to put to this - if one of your BMS's fails/disconnects when you're pulling a particularly high amperage load, shifting the whole load onto the other battery/BMS would cause that to disconnect too. As long as your vital loads (beer fridge et al) are low enough in current draw that a single battery/BMS could handle it, the 2x100Ah setup would provide marginally more redundancy than a single 200Ah with twice the current draw rating.
As noted above, the Will Prowse dissection videos were complimentary of the SOKs.
I went for a Victron DC-DC 12/12/30 in my camper, good choice.
 

Fah Kiew Tu

Curmudgeon, First Rank
9,864
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Tasmania, Australia
My system is going to be Alternator > AGM start battery > DC-DC charger > Lithium house battery.
The DC-DC charger handles the charge profile for the lithium and the alternator doesn't see it directly.
That's what my current setup is, except AGM not lithium. 3 years in, no problems at all.

The DC-DC charger has a relay that swaps from start battery to PV panel feed when the engine isn't running.

FKT
 

robalex117

Super Anarchist
My system is going to be Alternator > AGM start battery > DC-DC charger > Lithium house battery.
The DC-DC charger handles the charge profile for the lithium and the alternator doesn't see it directly.
One huge advantage of lithium batteries you are not going to get using the DC-Dc to charge is the amount of current they can take during the charge cycle. If your DC-DC charger is only 30amps well that is all you get. My setup they can take 100amps easy. But you do need to change your alternator to a lithium profile which is a little harder. I am a big fan of the Victron products. Use a bunch of them and their tech is nice.
 

eliboat

Super Anarchist
2,205
596
Yes
One huge advantage of lithium batteries you are not going to get using the DC-Dc to charge is the amount of current they can take during the charge cycle. If your DC-DC charger is only 30amps well that is all you get. My setup they can take 100amps easy. But you do need to change your alternator to a lithium profile which is a little harder. I am a big fan of the Victron products. Use a bunch of them and their tech is nice
Exactly. It is more common though for folks to be using a SLA battery as a capacitor to protect the alternator should a contactor Or mosfet open. I use my dc-dc charger to charge my start LA battery from the lithium bank and use a Sterling Alternator protect device to deal with any BMS shutoff events. This works well, and I can push 100+ amps to my house bank for as long as it needs it.

Kent island… I have a cheaper Chinese BMS that I got from Overkill Solar for some bench work at my house, and that has been pretty good for the price. Easily configured via an app and so far very reliable. If you ever have to replace the SOL Bms’s for whatever reason, the Overkill offerings are good value.
 

solosailor

Super Anarchist
3,887
716
San Francisco Bay
Most packs with internal BMSs have low amperage ratings for their relays...... ie 50A maximum usually. None of those internal BMSs will send a signal to the alternator to stop charging. Let's say you have an 80A alternator and one of your internal BMS units fail then the one remaining battery will be overloaded and close it's relay.
 

kent_island_sailor

Super Anarchist
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Kent Island!
One huge advantage of lithium batteries you are not going to get using the DC-Dc to charge is the amount of current they can take during the charge cycle. If your DC-DC charger is only 30amps well that is all you get. My setup they can take 100amps easy. But you do need to change your alternator to a lithium profile which is a little harder. I am a big fan of the Victron products. Use a bunch of them and their tech is nic
I only have a 60 amp alternator, so 100 amps of charging isn't happening. Even putting a 140 amp alternator on won't change that, the A4 alternator mount and pulley size limits you to about 50 some amps no matter what :(
* I have been told I can forget the DC-DC charger if I go into the regulator menu and limit the belt load to something like 80 or 90 percent instead of 100%. I also have temp sensor on the alternator, so that might help too.
 

efrank

Member
294
133
I only have a 60 amp alternator, so 100 amps of charging isn't happening. Even putting a 140 amp alternator on won't change that, the A4 alternator mount and pulley size limits you to about 50 some amps no matter what :(
* I have been told I can forget the DC-DC charger if I go into the regulator menu and limit the belt load to something like 80 or 90 percent instead of 100%. I also have temp sensor on the alternator, so that might help too.
This is a sometime in the future project for me.

I have read that the steady draw from your alternator should be significantly less than it's rating - like< 50%. For those of you that have done this, is that true?

I am also curious if there are any problems associated with having you shore charger hooked to the starter battery to DC to DC charger to lithiums.

It would be nice to just add the DC to DC charger and the lithium batteries without changing everything else.
 

nota

Anarchist
Li battery does not like other Li batterys if ?

when I was playing with Li batterys for 18v power tools
trying to hook together two 18's to get 36 to feed a 24v lawnmower
resulted in a burning 18v battery

just one data point but I did it real fire

likely did it wrong but ?
 

coltrek

New member
17
0
The Balmars have an amp manager feature to limit the output -
There is this from the Balmar Regulator manual, hope it is not already covered -

®LFP LiFeP04 Recommendations
Our LFP program is a generalized version of the recommendations provided by the top LFP battery manufacturers.
For best performance and compatibility, please consult your battery manufacturer and use the regulator’s advanced
programming features to adjust the LFP program as needed. LFP batteries are more sensitive to abuse than a
traditional chemistry battery and can fail catastrophically. It is HIGHLY recommended that the charging system as
a whole be installed or inspected by a qualified marine electrical installer that has experience with Balmar charging
system products and LFP batteries. The LFP profile is intended to work with the battery manufacturer’s battery
management systems (BMS). The LFP profile IS NOT a replacement for a BMS.

®Many LiFePo4 batteries have a Battery Management System (BMS) that may disconnect the battery
from the alternator as a protective action or when charging is complete. The regulator must be shut down
before the battery is disconnected .Running an alternator without a battery will damage the alternator
and may damage any attached system. This is doubly true if the battery can be disconnected during
high current charging, causing a load dump. The load dump can easily cause a high voltage spike
which will destroy the alternator’s rectifier, at minimum. This is not a warrantable failure. To reiterate:
THE ALTERNATOR MUST BE SHUT DOWN BEFORE DISCONNECTING THE BATTERY. THE ONLY
SAFE WAY TO SHUT DOWN THE ALTERNATOR IS TO TURN OFF THE REGULATOR. The preferred
method of turning off the regulator is disconnecting the regulator’s ignition (brown) wire, but if used as
an EMERGENCY ONLY shutdown, disconnecting the regulator’s power input (red) wire in addition to the
ignition wire has a very low chance of damaging the regulator.

®LFP batteries will readily accept a damaging amount of current. Applying too much charge current
to a LFP battery will, at the very least, permanently damage the battery’s capacity. It is CRITICAL to
ensure that the alternator is not capable of exceeding the maximum continuous charge current rating of
your battery (or batteries). As always, check with your battery manufacturer for specifics. Your battery
manufacturer may supply you with a “C-rate” for charging and discharging. The maximum amount of
charging current your battery can safely handle is determined by multiplying the “C-Rate” by the capacity
of the bank. i.e. 4x 100Ah 12V batteries rated at 0.5C charge = 400 Ah * 0.5C = 200amps MAX. If your
alternator is capable of outputting more current, at any time or condition, than the battery (or batteries)
can handle, you may use the Amp Manager feature on the MC-624 to lower the maximum field drive
output, and thereby lower the maximum alternator output current. See page 10 of your regulator
manual for details and instructions. Be aware that it is not an exact 1:1 correlation between field output
and alternator output, so start with more reduction (lower output) than you think you need and adjust
accordingly.

®It is strongly recommended that an alternator temperature sensor (MC-TS-A) be used when charging LFP
batteries. Given the extremely high charge acceptance rate of LFP batteries, the alternator will be driven
to full output for almost all of the charge cycle. This can cause overheating in automotive style alternators
resulting in a significantly shortened lifespan. When equipped with the MC-TS-A temperature sensor,
the MC-624 will help you protect your investment by reducing the field voltage to your alternator by 50%
when over the “AL1” temperature threshold. If you cannot use an MC-TS-A in your application, you should
monitor the alternator’s temperature (measure as close to the loop ends of the stator as possible) and
discontinue charging if the alternator temperature rises above the maximum recommended level. You may
also use the Amp Manager feature on your MC-624 to reduce maximum output until a tolerable alternator
temperature is maintained under all conditions.

®Most LFP battery manufacturers specify minimum and maximum charging temperatures to be from
freezing (32°F, 0°C) to around 111°F (44°C). Again, consult with your battery manufacturer for specifics.
When equipped with a MC-TS-B, the MC-624 can disable charging if the battery temperature exceeds
the “B1L” temperature threshold and re-enable charging when the temperature drops below the threshold.
This feature is meant to supplement, not replace, your BMS’s temperature protection features. “B1L”
should be adjusted to be slightly less than BMS’s temperature threshold. Note that the regulator does not
have the capability to prevent charging during low temperatures.
 

kent_island_sailor

Super Anarchist
26,946
4,907
Kent Island!
Li battery does not like other Li batterys if ?

when I was playing with Li batterys for 18v power tools
trying to hook together two 18's to get 36 to feed a 24v lawnmower
resulted in a burning 18v battery

just one data point but I did it real fire

likely did it wrong but ?
Only SOME lithium batteries can go in series. These obviously could not :eek:
 
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