AGM to Lithium, do I need to change Isolator or upgrade alternator?

[chin_k]

FWIW, I agree with Scott on the load on the alternator. You do not want to almost short out the alternator's outputs, which is what a lithium charger will be like during charging. Lithium has very little resistance, and will suck up all the electricity. You need to match the output of the alternator with the charger, and I don't think you are. Remember the current that the alternator needs to put out should be the continuous current rating. You do need a DC-DC charger to limit the current to help your alternator.

However I am more conservative on the SOC (state of charge) for my battery. I religiously keep it between 15% to 85% to prolong its life. In the scheme of thing, making it last 15 yrs vs 10 yrs is not big difference, but it is my personality to make things to last longer if it is not too inconvenient. The BMS in the lithium does not make it easy to keep its SOC within the longevity band unless you have a sophisticated version. My have a controller (in addition to the BMS) that I can specifically programmed to be within the 15-85%, but it maybe a bit of more work for your setup.

[Scott]

Just a few thoughts (don't take them word for word) ...

The easiest way is to use a dedicated lithium 120V charger (e.g. Victron IP22), a small solar controller just big enough for your solar array, and a DC-DC regulator if you're going to alternator charge. Then a low-standby inverter just big enough for your needs. I avoid transfer switches, converters, combiner jumpstart solenoids, and the other unneeded complications. Get a good large-gauge wire crimper, high quality copper stranded wire with matching tinned copper lugs (the Windy Nation stuff is great), and practice making proper cables. If you want, keep the stock breakers and house fuses. If you have a huge bank, get a T-class fuse and/or MRBFs on each battery. Get a shunt-based monitor ($40), and basically forget about what the BMS is doing. I don't bother with the bluetooth stuff at all (Chuck, you'll be too busy fishing). If voltage is right and state of charge (SOC) is cool, I can't really be bothered beyond that. I would focus on fusing and general safety, proper high-quality connections and wire, and a well laid out physical arrangement for the hardware.

[68camaro]

Scott, thanks for advice, and yes I spend nights in RV and days fishing. Rarely spend much time relaxing in Chinook except at night but I really love the lounge layout. I have wondered about making my own cables and heard a hydraulic crimper makes light work of bigger cables. For wire do I just used thin strand welder wire?

Battery switch over went well except since I was going to parallel from series my positive battery terminal bolt was not long enough for the extra cable. Local HW store was out of my size so I split the positive connections between the first and second positive battery connections. Not sure if this is best practice but I'll put all on one terminal when I get bigger bolt.

I had to drill holes in the compartment divider to get the wires to the 3rd battery. I definitely have room for a 4th battery but as you mention I probably don't need it since I am weekend warrior but they are on sale for $251 off so very tempting.

Also, these batteries are only 27 lbs compared to my 6volt at 72. My two old batteries were 144 lbs for 100ah, my 3 lithium are total 81 lbs (300ah) , and even if I add a forth (400ah) my weight is only 108 lbs which is still 36 lbs less than 6V. Working on the batteries at only 27lbs is much easier.

The other issue I have is trying to increase volts on my converter, I think I did it right but I never get a reading beyond what batteries SOC is.

Also my DC/DC charger will be here tomorrow so I will install then and definitely need to find or make cables.

Sorry no pics but for some reason I cannot add them to post????

[68camaro]

Here are pics of new battery bank.

[chin_k]

You can order cable that made to your specification, but a hydraulic is a great tool, but wasteful for a task that you will never going to do after a few cables were made. I would check Harbor Freight for things like that.

Anyway, you may want to describe or take picture of your cable setup, since the connection you said above sounds not quite right... We want you to get a good night sleep instead of worry about if the battery going to melt the wire and made you stranded at your camp.

About the SOC, it is just basically a look up table with the voltage and % of charge. For lithium, you need a very accurate voltmeter since the voltage difference between the middle 60% is very little.

[68camaro]

By the way, here is very interesting tech bulletin on best way to wire 3 or more batteries in parallel to even out draw from each battery I used Method 1, the standard but will redo to #2.

http://www.smartgauge.co.uk/batt_con.html

[Scott]

About the SOC, it is just basically a look up table with the voltage and % of charge. For lithium, you need a very accurate voltmeter since the voltage difference between the middle 60% is very little.

Do you monitor SOC in your LFP bank with a voltmeter?

[chin_k]

No, but that is how the SOC meter works in most application, I figured. Some may have temperature probe to adjust for the voltage changes, but for the most part, it is just a function of the battery voltage, nothing magical.

If anyone know more, or can correct my misunderstand, I am willing to learn.

[Scott]

The thing in Camaro's second picture is a shunt (in front of the left battery). It's a precision resistor that diverts a tiny percentage of current. That diverted current is measured for voltage delta against system voltage to estimate how much current is going though the main circuit. In a bidirectional application, the amount of power going into - or out of - the battery can be quantified, thereby providing a SOC based upon the bank's capacity. This value can then be displayed passively as a percentage.

[chin_k]

I think the shunt in Camaro rig is for his current meter (ammeter, which is actually a voltmeter that measure the voltage drop across the shunt). Some sophisticated digital meter does count the electrons via the ammeter, and use that to calculate the SOC, but all analog (and most digital) SOC meter is just use the voltage as an indicator of the SOC.