Connecting batteries in Series and Parallel

[richm]

Here's a picture of the more common 2S2P configuration.

[richm]

Originally Posted by BobG

I understand the need to match the length of conductors to even out the charging but I am not sure that that alone will do the trick due to variances in the connections, especially the Anderson connectors.

The anderson connectors themselves will have far more resistance and heat than the wires. So in practice, do vary the wire length to fit the distance, and instead get rid of the anderson connectors if this is a concern at all. If you need to swap batteries, unbolt the connectors at the battery.

Your hydraulic press sounds ideal for attaching lugs to the wire. There are lots of youtube videos that show the techniques. I'd use that if you can because it will allow you to use customized lengths fit to the installation.

[RangerMan]

Originally Posted by BobG

I have considered a generator but it requires gas unless converted to propane. If I get one I would convert it to propane. The problem I have with the generator is that the only place for me to store it out of site is under the bed and that isn't easy. The Honda 2200i won't fit through the access hatches to storage areas. I have thought about moving the spare tire and adding a box to the rear bumper for the generator but I would just as soon not even deal with one and the fuel it needs, whether gas or propane.


The 2 batteries I have are 46 lbs each so 91 lbs total for 170 Ah at 24 volts or 340 Ah at 12 volts. I do not know what the Escape batteries weigh or how many usable amp-hours are available but the weight has to be close to a trade off. Hopefully I will be able to cool the trailer in 15 minutes at bed time and then maybe another 15 minutes a half hour later. This worked for me last year but I plugged in.



Hopefully I don't have to add 2 more batteries but just in case, I want to know that I can do it if necessary.

If you do decide on a gen and convert it to propane be sure to look at the Hutch Mountain Kit. Very easy to install and works great.

.

[tdf-texas]

Originally Posted by richm

If the wire is rated for 250A continuous, you don't need a fuse. If it's less, then add a fuse for something at or below the continuous Amps rating.

Very bad advise! All battery cables should be fused - both for overcurrent protection for the inverter and for short circuit protection.

[Brian B-P]

Originally Posted by richm

It is far more common to first wire pairs of batteries in parallel, and then connect the parallel pairs in series. That way, you can use a just one BMS to balance all of the batteries.

Originally Posted by richm

Here's a picture of the more common 2S2P configuration.

That's true for individual cells, but these are 4-cell units and they are not just bare cells; they are complete drop-in battery replacement units with an internal BMS (battery management system) in each unit.

[Brian B-P]

Originally Posted by richm

If the wire is rated for 250A continuous, you don't need a fuse. If it's less, then add a fuse for something at or below the continuous Amps rating.

Originally Posted by tdf-texas

Very bad advise! All battery cables should be fused - both for overcurrent protection for the inverter and for short circuit protection.

True, a fuse is needed, but the unit's specs include:

Short Circuit Current: Fused @ 300A

In a simple installation (no parallel connections) with sufficient cable and connector capacity the built-in fuse would be sufficient.

The cable and connectors to these units need to be rated for at least 300 amps, ,because that's what the fuse will allow. If the connections from two units are combined (in parallel), either cable and connectors rated for at least 600 amps or a fuse rated lower than the cable or connector capacity is required; in this case, that certainly means a fuse.

There is no reason to fuse the power source to protect the inverter from overload - the inverter does that itself. Any reasonable power supply configuration to the inverter will be capable of - and fused for - far more than 3000 watts.

[BobG]

Thank you everyone for your help. I am sleeping better instead of thinking at night.



Rich - I had not thought of connecting the initial batteries in parallel using a busbar. I see how this would be a way to work around the Anderson connectors.



However, something I just realized is that the 12 volt and 24 volt 3000watt inverters might be 2 different models. The service manual I have been reading shows specifications for both in the same specification tables and I had been thinking that it was an option on how you choose to operate the inverter.



I will need to make sure to get fuses in the right places no matter what I do.



Each battery is fused internally with a 300 amp fuse.


There is a lot to be said for buying from a professional but it is also a lot of enjoyment for me to learn new things. On my old cruising sailboat I enjoyed learning how each system worked, how to install new systems and maintain them. Also, what spare parts to carry. I sold the boat to an airline pilot who was the opposite. Years later I read what he posted. He said he should have learned how everything worked and how to do the work himself. My approach was also influenced by experienced cruisers who told me at the beginning to do everything myself or at least learn how it should be done and to check all work done by others. Life depends on it. A trailer is not so critical but I enjoy learning nonetheless.

[BobG]

The inverter specifications recommends a 300watt fuse for the 24volt system and 400watt fuse for the 12 volt system. I have a note that it should be a class T fuse. I don't know why I wrote that note. I will have to verify it. It sucks when I make notes and go back later and wonder why I said that.

[richm]

Originally Posted by tdf-texas

Very bad advise! All battery cables should be fused - both for overcurrent protection for the inverter and for short circuit protection.

Just to add some context here: The lithium batteries will have a BMS that includes over-current protection, that disconnects at some maximum rated current. It's possible to design a system for a smaller maximum, and in that case, the wire is rated for a smaller amount and you need a fuse to limit the current that flows via that wire.

If the wire can carry more than the BMS' maximum current, you don't need a fuse for the individual wire itself, if there is to be a fuse at the distribution panel.

So yes, you need protections that limit the current. They can also be in the battery, and at the distribution panel.