Home charging van lifepo4

[delvxe]

Hi all, I searched, I promise and couldn’t fit the info I need. I have a 120ah lifepo4 battery I built from prismatic cells in my van. It charges via a small solar panel permanently mounted and the alternator when I am driving. Recently I haven’t been driving much and my always-on fridge is starting to drain the battery. Turning the fridge off is not an option. I’d like to be able to cheaply charge the battery while parked. It doesn’t need to be a fancy system, just a temp extension cord from the garage is fine.

Here are my questions.
1. I picked up a 4 amp charger from the internet that says it is for lifepo4 batteries. (This one: https://a.co/d/gfdUN8z). Can I safely just hook this up to the main pos and negative on the battery pack and it will slowly charge or do I need to connect it to the BMS or charge controller somehow?

2. Do I need to “watch over it” or will it stop charging when the pack is about full.

Thanks so much!

 

[Tomthumb62]

A 4A charger is likely only enough to run your fridge but not charge the battery. Get more charging. Either more panels or a bigger shore charger or both. The Victron ip22 series are nice. You can get a like-new open box of the Victron IP22 30A for under $200. I think I paid about $150 for mine. It’ss sweet charger with Bluetooth for programming it perfectly.

They also have lower amp models, I think 18A or 20A. But the 30A model can be set for half power at 15A, which would be perfect for your 120Ah battery when combined with your current solar panel. If you ever add more battery capacity, just switch it back to 30A for faster charging.

With any decent charger designed for lifepo4, you don’t need to watch over it. It will drop to float (and the Victron will also later drop to Storage voltage) when full.

Yes you just connect it directly to the battery positive and negative. Don’t connect it to the solar charge controller or the BMS.

 

[Frank in Thailand]

No (!) You should NOT connect it to the battery positive and negative.

Why on earth would anyone want to bypass an BMS??

Yes, you connect it to the battery positive and the p- of the BMS.

This way there is controlled charging.

We do not have enough information about the refrigerator, and if it's in use (door opened frequently) nor the temperature.
So impossible to know it's power draw.

It can be 1 or 4A and anything in between.

We also don't know how long the setup will stay like this, or the imbalance of the cells now.

If the cells are perfectly balanced, yes, the charger might be connected to the battery directly, as it should respect the total pack maximal voltage.
Any imbalance...
The BMS is not included to save your ass...

Like driving around without safety belt and no airbag.

Sure you can.
Just don't have any misfortune...

 

[Tomthumb62]

No (!) You should NOT connect it to the battery positive and negative.

Uh, what?!

He’s talking about connecting a battery charger to the battery. You want to connect it to the main battery positive and negative terminals. Which are connected to the BMS if he’s built his battery properly.

 

[Frank in Thailand]

Uh what?

You charge your battery without BMS??
Or you use only balancers and hope for the best??

Bms is to be used during charge and discharge, no matter the source or electricity.

Unless we are talking about individual cells..
Yes, those are the ONLY one you can charge without BMS IF you have the correct charger. (Max 3.65v)
(His link is about an 14.6v)

As soon as you have S4, 4x nominal 3.2 volt..
And charging it with an "12 volt lithium charger" (max 14.6v) ( 4* 3.65v)
You are just "hoping for the best" if you are bypassing the BMS.

Say 2 cells at 3.55, one at 3.6 and the next.. Indeed.. the BMS would have hit the brakes... Topped off (balance) and let the 2* 3.55 catch up.

No BMS you are overcharging one cell in this example with 3.65 + 0.1 + 0.1 + 0.05= 3.9v..

That's why people use a BMS

 

[Tomthumb62]

You charge your battery without BMS??

I said no such thing. His battery has a BMS and the terminals are connected to that. Charging at the terminals will then go through the BMS. You’re not reading my words well.

 

[Frank in Thailand]

BMS B- is connected to the main negative battery terminal.

Then the load (charge or discharge) is connected to the P-

Obviously you can build a box around your battery, and a lead/ cable from the main Positive terminal to a connection and call it Batt+
And make a lead / cable from the P+ and call it Batt-

You can call them the battery positive and negative.

They are not.
They are the battery positive and the BMS P-

The BMS sit between the Battery negative terminal and the point where you connect everything.

That doesn't make it "impossible" to connect a charger to the negative terminal.

Something he explicitly asks.
And he should not.

You told him to do so.
He should connect after the BMS not before the BMS

 

[Frank in Thailand]

Answer to the question:
Can I safely just hook this up to the main pos and negative on the battery pack and it will slowly charge or do I need to connect it to the BMS or charge controller somehow?

The connections / terminals you use to connect the charge controller to the battery (at the battery) are the same connections / terminals you will use for the external charger.
So double, lugs or clamps, depending on your current setup.


Charger purchased by OP


The BMS will automatically be connected this way and your battery protected.

If you can share a picture of the current setup, we can point exactly where to connect

 

[Tomthumb62]

BMS B- is connected to the main negative battery terminal.

Then the load (charge or discharge) is connected to the P-

Obviously you can build a box around your battery, and a lead/ cable from the main Positive terminal to a connection and call it Batt+
And make a lead / cable from the P+ and call it Batt-

You can call them the battery positive and negative.

They are not.
They are the battery positive and the BMS P-

The BMS sit between the Battery negative terminal and the point where you connect everything.

That doesn't make it "impossible" to connect a charger to the negative terminal.

Something he explicitly asks.
And he should not.

You told him to do so.
He should connect after the BMS not before the BMS

No one says b- or b+ when they mean battery positive and negative. You’re technically correct but it’s not the real world language used, at least not in the context of the OP. In my opinion.

But since you bring it up, we should make sure he’s not intending to bypass the BMS.

He’s given us no evidence that he has not wired his battery properly and intends to bypass the BMS.

 

[Frank in Thailand]

I said no such thing. His battery has a BMS and the terminals are connected to that. Charging at the terminals will then go through the BMS. You’re not reading my words well.

Assumptions..
Did you see his battery?

Know his setup?
For all you now his only knowledge is from the Amazon picture of the product he bought.


Connect like this

You don't know.

When you ask someone with limited electriconics knowledge what are the terminals of a battery, this is what they will think ...

Edit: actually... Funny that they choose a lead acid battery as example to promote lithium battery charger hahaha...

 

[Tomthumb62]

You make a good point. None of us has seen his battery wiring. I assumed he built his into a case so the terminals (b- connected to the BMS) are the only things available for connection. Similar to what is seen in the Amazon photo. In a van situation, I would think this obvious to have a case of some kind as exposed live wiring in the confines of a van is dangerous.

 

[Frank in Thailand]

I would not have thought anything about it, except for his explicit mention and question related to the BMS.

do I need to connect it to the BMS or charge controller somehow?

If he can access it separately..
It's not a closed box.

The "somehow" indicate to me a limited knowledge on how to connect.

Without disrespect, I'm taking my mother (78) or an 8 year old as technical insight...

And try to take it from there.

I hope @delvxe can share pictures.
Or perhaps our both explanation is enough to find where to connect.

4A, 12v, 40 watt usable energy..
That's not a lot to power a refrigerator.
But... No idea of the size.

Victron has really nice but expensive toys. I personally would buy a second one and in parallel (clamp on clamp)

For higher capacity, absolutely a NO-GO. Yet.. 2 x 4A ...
Not much can go wrong.

Anyways..
Hopefully @Tomthumb62 and my sparring gave enough insight ?

 

[delvxe]

Thank you all for the feedback. I think I am hearing it is safe to leave connected to the main pos and neg for the occasional overnight use since it is so low power. Could I leave it connected for a long time?

It may not very quick (which is fine) I just need something very infrequently to help keep the battery from entirely draining if it sits for an extended period.

Some responses to things that came up in the thread:
The fridge has a pretty low draw ~4amps when the compressor cycles on.
The battery is a home brew with exposed terminals, wires, and BMS, but it is in a small dedicated compartment, secured and snug and the terminals and wires are protected with a rubber cover - similar to this photo.

 

[Tomthumb62]

Thank you all for the feedback. I think I am hearing it is safe to leave connected to the main pos and neg for the occasional overnight use since it is so low power. Could I leave it connected for a long time?

It may not very quick (which is fine) I just need something very infrequently to help keep the battery from entirely draining if it sits for an extended period.

Some responses to things that came up in the thread:
The fridge has a pretty low draw ~4amps when the compressor cycles on.
The battery is a home brew with exposed terminals, wires, and BMS, but it is in a small dedicated compartment, secured and snug and the terminals and wires are protected with a rubber cover - similar to this photo.

I think @Frank in Thailand and I were coming at different angles here. He brought up some excellent questions. I think your use (misuse) of some tens especially throwing things “do I hook up to the BMS or just main +/-?”) raised some valid concerns. Safety is paramount here as we’re talking about thermal runaway if you’re not smart about what you’re doing. From what I can tell, you’re fine.

To be sure, when you say,

I think I am hearing it is safe to leave connected to the main pos and neg for the occasional overnight use

…what I think you mean by “main positive and negative”, you mean the positive and negative TERMINALS, of which the negative is connected to the BMS. Is this correct?

I think what Frank thought you meant was the technical “battery + and battery -“ the wires that carry power before the b- connects to the BMS. If this is the case, then this is not a safe way to do it, but I don’t think that’s what you meant.

 

[Frank in Thailand]

This type of chargers are intended to stay connected for several days, even longer.

Usually the lithium battery is "external" like removed from e-bike, and charged at home (or such)

I doubt I'm the only one that leaves a device on a charger for a few days (or weeks) forgetting about it.

Amazon has usually better quality then AliX.

And.. you aren't keeping it charged, but are continuous charging (and discharging)

For the batteries it's OK.
If the charger can last a long time?

For $27 bucks.. it should!

My $6 car battery charger and tickle has been on a battery for several months.
Still working great ?


At 4.5 times the price..
It should be at least double the quality

From engineering point of view..
It's a tiny change, a charger from14.7v (lead acid) to 14.6v..

And honestly..
There isn't much more intelligence behind it.

Most of it is taken care by the chemistry of the battery

Constant Current/Constant Voltage.

I'm sure the Victron $200 charger is "military grade" (Marine, Medical, Emergency responders) and will last a lifetime.
For occasional use..
The $6 or $27 will do just fine

 

[delvxe]

…what I think you mean by “main positive and negative”, you mean the positive and negative TERMINALS, of which the negative is connected to the BMS. Is this correct?

Very likely I’m using imprecise terms. In the photo, you can see I am connecting the charger to the terminals circled in red and brown. The terminal in brown is connected to the BMS. Is this the proper way to connect this? And it shouldn’t overcharge the battery?

 

[42OhmsPA]

Very likely I’m using imprecise terms. In the photo, you can see I am connecting the charger to the terminals circled in red and brown. The terminal in brown is connected to the BMS. Is this the proper way to connect this? And it shouldn’t overcharge the battery?

No.
As Frank and Tom have said you need to connect the negative of the charger to the other side of the BMS. If you connect it to the post circled the charger will bypass the BMS.

 

[timselectric]

Very likely I’m using imprecise terms. In the photo, you can see I am connecting the charger to the terminals circled in red and brown. The terminal in brown is connected to the BMS. Is this the proper way to connect this? And it shouldn’t overcharge the battery?

No, that's wrong.
Move the negative charger wire to the other side of the BMS.

 

[delvxe]

No.
As Frank and Tom have said you need to connect the negative of the charger to the other side of the BMS. If you connect it to the post circled the charger will bypass the BMS.

Thanks so much. I will do that and this makes a lot of sense. The other side of the BMS (black wires) is just connected to a ground on the van body. Are you saying I need to connect somewhere in those wires? Maybe to the same ground?

 

[timselectric]

I also see two black wires on your picture. Coming in from the bottom of the picture. One is connected in each of the circles. Where do these wires go? They are also connected to the wrong places. They are bypassing all protections.
Nothing should connect directly to the battery cells. Except for the BMS and your positive side breaker.