Inverter/chargers in HDT

[SuiteSuccess]

Okay need someone to explain the electronic theory (in simple terms) as to optimal way to hook up inverter/charger.  So most HDTs have 3 or 4 twelve volt batteries connected in parallel.  Assume appropriate size cable for the “runs” to the inverter from the batteries.  Also assume the  + (positive) from battery 1 is jumped to the + of battery 2 , and so on for 3 and 4.  The - (negative) is the same completing the parallel connection of the batteries.  Should the + cable run to the inverter/ charger be connected to battery 1 + and the - cable run to the inverter/charger to the - on battery 1 OR should it be + on 1 and - on battery 4?  If the latter is this because of resistance in the jumpers from battery to battery?  It seems to me + to 1 and - to 4 makes the most efficient configuration for inverting and charging especially since the first configuration when charging might result in small voltage loss to the furthest battery in the string causing unbalanced charging?  I’m also assuming the charger has enough amperage to charge four batteries.

[Randyretired]

Connect to opposite ends.  + on one battery and the - on the far battery.  Be sure to wire and fuse properly.  Short of buss bars this will be best for balancing the batteries.

[NeverEasy]

Carl, I have seen where the recommendation is to hook both + and - connections to the center most point of the batteries.  However, I don't see the need if the batteries have a good connection to the bus.

Question, what size inverter (watts) will you install.  For a true calculation of current, add 10% to that for the internal workings of the inverter (overhead).  Use that to calculate the amps with the formula Current equals watts divided by voltage.  I = P/V.   I have found that most installations max out the size of the inverter due to cable size needed to support anything bigger than 1500 watts..  I = 1515/12 volts = 126.26 amps.   

The length of the cable run is very important.  Mount the inverter as close to the battery source as you can.  You must calculate the length using both the positive cable length + the negative cable length.  Measure in meters to use the following chart.

This is a good site to calculate cable size needed:  DC Cable Size Calculator | Fabhabs.  

As an example of using anything bigger than a 1500 watt inverter, let's say you are going to install a 2400 watt inverter.  The max current is 202 amps.  Put that in the above chart with a 1 meter cable length and the chart will show you that there is no cable big enough to support that installation.

At one of the Kansas HDT rallies, I was asked to look at a 2400 Watt inverter install.  I found that the installr used a 4-AWG 2 meters (4 meters total) away from the batteries.  To protect the cables, a 40 amp fuse was put inline thereby effectively limiting the output of the inverter to (P=I x V) or 40 x 12 = 480 watts.  The size of the inverter than became a 480 watt inverter.  Shit!

 

 

 

Edited February 22 by NeverEasy
Typo

[SuiteSuccess]

1 hour ago, Randyretired said:

Connect to opposite ends.  + on one battery and the - on the far battery.  Be sure to wire and fuse properly.  Short of buss bars this will be best for balancing the batteries.

So you’re saying the latter option.  Positive on battery 1 and negative on battery 4 or vice versa. That makes the most sense for balanced charging and the way I’ve always done it but really couldn’t explain the REASON I do it that way. 

[SuiteSuccess]

57 minutes ago, NeverEasy said:

Carl, I have seen where the recommendation is to hook both + and - connections to the center most point of the batteries.  However, I don't see the need if the batteries have a good connection to the bus.

Question, what size inverter (watts) will you install.  For a true calculation of current, add 10% to that for the internal workings of the inverter (overhead).  Use that to calculate the amps with the formula Current equals watts divided by voltage.  I = P/V.   I have found that most installations max out the size of the inverter due to cable size needed to support anything bigger than 1500 watts..  I = 1515/12 volts = 126.26 amps.   

The length of the cable run is very important.  Mount the inverter as close to the battery source as you can.  You must calculate the length using both the positive cable length + the negative cable length.  Measure in meters to use the following chart.

This is a good site to calculate cable size needed:  DC Cable Size Calculator | Fabhabs.  

As an example of using anything bigger than a 1500 watt inverter, let's say you are going to install a 2400 watt inverter.  The max current is 202 amps.  Put that in the above chart with a 1 meter cable length and the chart will show you that there is no cable big enough to support that installation.

At one of the Kansas HDT rallies, I was asked to look at a 2400 Watt inverter install.  I found that the installr used a 4-AWG 2 meters (4 meters total) away from the batteries.  To protect the cables, a 40 amp fuse was put inline thereby effectively limiting the output of the inverter to (P=I x V) or 40 x 12 = 480 watts.  The size of the inverter than became a 480 watt inverter.  Shit!

 

 

 

Chet, 

I have a Xantrex Freedom 1800 HF which I installed years ago with 3/0 cable and short runs.  I connected to battery 4 positive and battery 1 negative but really had no good facts to support that configuration. I’m putting four new batteries in (one battery died [tested] all four only 22 mos old) and was questioning whether my connection configuration might have been a culprit. BTW that battery was #4 and had little electrolyte while all others had plenty of fluid. Also I’m fused properly. (You helped me choose the size years ago.)

[NeverEasy]

I plugged in the 1800 watt inverter into the wire size calculator.  Using 3/0 cable, you are good out to a 3-meter cable run with an acceptable loss of 3% voltage.  Stay under a 3-meter positive cable and 3-meter negative cable and you are good.    

Also, you might want to look at using a chassis return.  Note the button (Include return?) below and what it says next to it.  Both tables shown below.  With chassis return, cable size could drop to !/0,  

[Chad Heiser]

Always pull from opposite sides of the battery bank.  If you pull from the same battery in the bank, that battery gets used more than the other batteries.

[jenandjon]

This was before I installed new batteries, I did have it hooked up to one battery but now I have the positive on the left and negative on the right. I used 2/0 welding wire. Kowing what I know now I should have used bigger wire. There is fuse link that has never blown yet. But the only thing it runs is a mini fridge and kids phone chargers. 

The only reason I used that particular inverter was because it was laying around the shop and it was free. 

[NeverEasy]

Here is an interesting post of how to connect batteries in a four-battery configuration.  For an equal charging and loading, hook the positive to the center left battery and the negative to the center right battery.   

How to Configure a Battery Bank – Windy Nation Inc

Edited February 23 by NeverEasy
did not read the whole article

[SuiteSuccess]

11 minutes ago, NeverEasy said:

Here is an interesting post of how to connect batteries in a four-battery configuration.  For an equal charging hook the positive to the center left battery and the negative to the center right battery.  I would assume then that the load on the batteries should be hooked up in a similar fashion.  He shows examples of the other ways to hook up batteries.  

How to Configure a Battery Bank – Windy Nation Inc

Chet,

That is EXACTLY the explanation I was looking for.  Thank you.  It just seemed logical to even my grade school electronics brain that resistance was the culprit in the whole setup.  Minimize resistance whenever possible.