Add on pack connector.

[boxydan]

I have some 75ah gel batteries coming.

They come with internal threads (M6) and the battery harness connects via ring terminal.

For an add on pack, can I stack the additional terminals on top or do I need a multi terminal adapter?

What would be a reasonable gauge battery cable for the add on?

[Burgerman]

Stack them.
Cable? 6sqmm is what I would use and a 60A fuse. Connect with a XT90. Others may have different ideas! But thats what I would use.
I presume you mean lithium addon.

[boxydan]

Yes lithium add on.

Thanks.

[Burgerman]

When using an addon pack, it pays to use a series silicone 50 or 100A Diode for a few reasons.
1. As you sischarge the lead and lithium together the lithium takes the bulk of the load. Because its voltage is a little higher. Esp under load. Ideally you want them to be used more equally together.
2. As you drive the lithium will become dangerously used up before the lead battery is. And before the battery gauge starts telling you this.
3. As you charge the lead with your usual charger this also tries to charge the lithium. This doesent balance the cells. So could be bad.

A series diode stops the above as there is a .7V drop across the diode. So the batteries discharge at a closer rate. You take it from both. It also stops the XLR socket and the normal charger from charging the lithium pack.

It DOESENT stop the lithium charger from charging your lead battery though. That can be a good thing. As your hobby charger will charge the lithium, balance it and charge the lead battery too. You just need to set the hobby charger correctly.

[shirley_hkg]

I started using add-on in 2007, with a BMS which balanced at 3.5v.

Yes. Put diodes in series to let both batteries work closely.

I put diodes in both ways , so that the stock charger's volt to add-on is reduced to 28.2v

This allows user to keep his stock charger so no need for a new one .
Charge both batteries in one go. Very convenient.

[boxydan]

So bare with me....me and Gustav Kirchhoff have not shared a brewski in a while.

Diodes as I recall prevent current flowing in one direction.

Shirley mentions putting diodes in series which I understand would be needed to increase the voltage rating of the single diode.

Then also notes putting in diodes both ways.

This is where I am getting lost.

I would have the gels wired in series together as a 24v unit which then wired in parallel to the 8s add on. Getting the 8s Li unit dropped 0.7v bring it more inline with the voltage of the lead gels so they are more balanced.

Where does the diodes in series and "both ways" come into play?

[Burgerman]

A silicone diode DROPS the votage in the forwards direction by around 0.7V which allows the lead battery and the lithium battery to discharge at a closer level so that both get used as you drive. More or less.
So the FORWARD voltage drop across a large 50 to 100A diode is around 0.7V.
The diode voltage can be 35V upwards. Typically 100 plus. Doesent matter.

Adding two in SERIES would mean 1.4V forward drop. (and nothing will flow through a diode in reverse. You dont need that. I think he meant fitting two, back to back, in opposite directions. By "series" he means simply in series with the addon pack. Not using 2 in series.

Because that will allow the chairs lead charger to also charge the lithium at 0.7V less than the lead battery. Thats a GOOD thing. So now theres a voltage drop of 0.7V in BOTH directions.

[shirley_hkg]

[boxydan]

I feel I am missing a diode. Here is what I have....

https://crcit.net/c/8604293cdf3d435986c6b9f968367717

Corrections are welcomed

[shirley_hkg]

Just like that.

Diodes are for dropping voltage , not for regulating direction of current.

[ex-Gooserider]

Make sure you use a BIG (high current capacity) diode, so that it doesn't overheat and turn to smoke... At least the 10A diodes Shirley pictures, or even something like an alternator diode...

ex-Gooserider

[Burgerman]

E.G
https://www.digikey.co.uk/en/products/d ... 00/2039191
These would be super safe.

Theres a slightly better 100A 45V one too but thats out of stock.

[shirley_hkg]

I use 8 for discharge and 4 for recharge, on the -ve path. Multiple diodes have much larger surface area, so no need of a heatsink. I hang it in open air for cooling.

[boxydan]

Diode goes on the negative? I thought they were on positive side.

[LROBBINS]

Doesn't matter,

[shirley_hkg]

Doesn't matter,

I just don't like the +ve hanging out in the air.