Lithium batteries

The best YouTube source is Will Prowse. He tears apart lots of batteries. Some of the cheaper LiFePo4 batteries have no low temp sensor. He checks this by dipping the sensor in ice water.

wa8yxm wrote:

pianotuna wrote:

time2roll wrote:

pianotuna wrote:
The "cold" end is the dangerous part. Charge below that, and the batteries become expensive door stops.

Or the BMS stops the charging at low temperature and protects the battery until it can be determined why the heating system has failed.

You left out part of what I said which was there is no need to have heaters cut in at 50 f.

Warning.. there is a video where an engineer (We like to take things apart as well as build 'em) took apart a LiFePO4 battery.. Down to the cells (He did not take them apart)

The battery clearly claimed to have both low and high temp sensors and protection (High temp is to prevent thermal runaway and fires.. Rare with LiFePO4, common in some other LiOn types)

IT did have a high temp sensor.. But no low temp at all. He tested.
So just because it says it's low temp protected... Does not mean it is.

that was a store bought boxed one and what that engineer may have missed is that one temp probe can be used for both high and low limits.. when you build them yourself you know exactly what they have in them. high temp is mainly to prevent charging when the battery is to warm, not for thermal runnaway, as LifePO4 is highly resistant to that. in fact if you have ever seen the vido of what it takes to get a LiFePO4 to actualy catch fire, its pretty amazing..

pianotuna wrote:

time2roll wrote:

pianotuna wrote:
The "cold" end is the dangerous part. Charge below that, and the batteries become expensive door stops.

Or the BMS stops the charging at low temperature and protects the battery until it can be determined why the heating system has failed.

You left out part of what I said which was there is no need to have heaters cut in at 50 f.

Warning.. there is a video where an engineer (We like to take things apart as well as build 'em) took apart a LiFePO4 battery.. Down to the cells (He did not take them apart)

The battery clearly claimed to have both low and high temp sensors and protection (High temp is to prevent thermal runaway and fires.. Rare with LiFePO4, common in some other LiOn types)

IT did have a high temp sensor.. But no low temp at all. He tested.
So just because it says it's low temp protected... Does not mean it is.

pianotuna wrote:

time2roll wrote:

pianotuna wrote:
The "cold" end is the dangerous part. Charge below that, and the batteries become expensive door stops.

Or the BMS stops the charging at low temperature and protects the battery until it can be determined why the heating system has failed.

You left out part of what I said which was there is no need to have heaters cut in at 50 f.

There was no reason to talk about cold damage at 50f and above and yet there it just fell out.

May as well talk about 150mph speed rated tires for an RV.

time2roll wrote:

pianotuna wrote:
The "cold" end is the dangerous part. Charge below that, and the batteries become expensive door stops.

Or the BMS stops the charging at low temperature and protects the battery until it can be determined why the heating system has failed.

You left out part of what I said which was there is no need to have heaters cut in at 50 f.

pianotuna wrote:
The "cold" end is the dangerous part. Charge below that, and the batteries become expensive door stops.

Or the BMS stops the charging at low temperature and protects the battery until it can be determined why the heating system has failed.

S Davis wrote:
I only plan on 350 amps max so two 250amp BMS should cover it.

Yes dual 250'tis will be fine.

S Davis,

I chose to have a single switch for each battery bank. They are 1000 amps contacting and cheap.

If one should end up with burned contacts--the other can carry the load.

This is the format, but I'm not sure if it is 1000 amps contacting.



https://www.harborfreight.com/battery-cutoff-switch-63425.html?utm_source=google&utm_medium=cpc&utm_campaign=12144811130&campaignid=12144811130&utm_content=117789284558&adsetid=117789284558&product=63425&store=&gclid=Cj0KCQiAvqGcBhCJARIsAFQ5ke5Q18Ke31j8nipZjUS1sQMhQdbVx5Jme3ESiNo1xlbvh3RYhRcmulYaAskbEALw_wcB

I only plan on 350 amps max so two 250amp BMS should cover it.

S Davis,

Looks like a good system.

There is no need to heat the batteries at 50 F.

Heat and cold are the enemy but Li can tolerate between -4 f to 140 f. I'd choose to shave off 14 f on both ends. i.e. 10F to 126 F.

The "cold" end is the dangerous part. Charge below that, and the batteries become expensive door stops.

The "hot" end, if exceeded does reduce cycle life.

I'm going to go out on a limb and say I think the BMS is a little bit small amperage wise. I'd be more comfortable with 300 instead of 250.

If you intend to "moochdock" and plug into 15 amp shore power, load support is a wonderful feature. I would never buy an inverter/charger without that feature.