Voltage regulators ?

[markojr]

I want to install a 1000 watt inverter in my truck. My inverter goes into low voltage alarm at 11 VDC and shuts down at 10.5 VDC. I am planning on using 3 or 4 deep cycle batteries. To use more of the batteries potential I would like to connect the batteries in series but am having trouble finding some way of charging it from my 12 VDC system and also getting the 36 or 48 VDC back down to 12 VDC at 100 amps. Anyone have any suggestions? Thanks

Currently I have a power resistor between my starting battery and
my aux batteries so I am not worried about how much my alternator can handle. From what I hear though it sounds like I will loose to much efficiency trying to put the batteries in series. I was just looking for an efficient way to use about 6 volts instead of using 1.5 volts of capacity. Thanks for the input. If anyone has any other ideas I would like to hear them. Thanks

 

[LTX71CM]

You want to wire the batteries in parallel. There will likely be more losses in raising the voltage just to lower it again to avoid a low voltage cutoff. The cutoff is a safety measure for your batteries and connected devices. Deep cycle batteries can go much lower than standard car starting batteries but I think you'll find connecting the batteries in series will still provide ample runtime. If you're using a stock alternator and regulator make sure they're up to the task!

 

[RCinFLA]

Make sure you are using large enough wire. Voltage drop for a 10 feet pair (+/-) run at 100 amps is as followed:

#0 = 0.25 vdc
#2 = 0.40 vdc
#4 = 0.80 vdc
#6 = 1.31 vdc
#8 = 2.00 vdc
#10 = 3.20 vdc

For a 1000 watt 12v inverter you should be using at least #2 unless wire run is short.

 

[MikeMl]

12V at 100A is 1200W, while the alternator in your truck is likely only rated at 60A, or about 720W, so your batteries will be running down even at highway speeds. Your inverter is probably less than 85% efficient, so your input drain is even higher than 100A.

 

[markojr]

Currently I have a power resistor between my starting battery and
my aux batteries so I am not worried about how much my alternator can handle. From what I hear though it sounds like I will loose to much efficiency trying to put the batteries in series. I was just looking for an efficient way to use about 6 volts instead of using 1.5 volts of capacity. Thanks for the input. If anyone has any other ideas I would like to hear them. Thanks

 

[MikeMl]

FYI, Flooded Cell Starting batteries (like the factory-installed one in your truck) should never be discharged below 80% of their AH capacity, or 11.5V, whichever comes first, period.

A "deep-cycle" storage batteries have greatly different construction. They can be discharged to ~11.0V, while using up ~90% of the AH capacity. Discharging below that will kill them very quickly.

 

[adamey]

What do you plan on running off the inverter? I assume that you'd want the batteries to charge while the truck is running, and use the batteries to operate some electrical equipment when the truck is off.

I've done numerous installations like these for a fleet of cable installers. I used a battery isolator (the relay type, not the diode type). Basically it detects the charging voltage of the alternator when the engine is running and connects the secondary batteries to the main battery/alternator so they can charge.

When the engine is shut off, the relay detects the drop in voltage and disconnects the secondary batteries. Many of these relays also have a manual connect switch which would allow you to use the secondary batteries to help the main battery when starting your vehicle (in cold weather or if you left the lights on by mistake).

Here's one example:

http://www.colehersee.com/pdf/hot_feed/D-617_SmartBatteryIso.pdf

As mentioned, use deep cycle batteries (like marine or RV batteries). Regular batteries won't last long in this application. Buy all the batteries at the same time and make sure they are exactly the same. Mixing different sized batteries is not a good idea - they won't charge or discharge at the same rate and for sure one will fail sooner.

Also as mentioned, your alternator would never put out enough power to run the inverter when the vehicle is running (not at full load, anyway). This is why I asked about what you plan on running off the inverter.

Connect the batteries in parallel and use #2 wire, keeping the leads as short as possible (inverter should be mounted right next to the batteries). You could use something smaller (like 8-10 gauge) for the wire from the vehicle battery to the isolator to provide the charging voltage to the secondary batteries.

 

[Diver300]

I was just looking for an efficient way to use about 6 volts instead of using 1.5 volts of capacity.

I think that you have misunderstood how batteries behave. The voltage on a lead-acid battery is a very poor indicator of charge. If stop using a 12 V lead-acid battery at 10.5 V, you have used just about all of its capacity. In fact, that voltage is already risking damaging it. If you carry on using it down to 6 V, you will only get a tiny fraction more time, and you will be doing some damage.

https://www.yuasaeurope.com/images/uploads/uk/images/charts/NP/np-discharge-characteristic.jpg shows the curves. When the voltage gets down to 11 V, the battery is basically discharged and the voltage will fall very rapidly at that point.

If you don't mind an analogy, the voltage-capacity characteristics of a lead-acid battery is a bit like the pressure-capacity characteristics of a water tank in the roof of a house. As the water is used up, the level in the tank falls, and the pressure drops a bit. When the tank is empty, and all that is left is the water in the pipe, and the pressure falls much faster and there is basically nothing left.

I suspect that you were thinking that the battery characteristics were more like that of a tall tank with the base at ground level, where the amount of water remaining is proportional to pressure. Unfortunately, batteries aren't like that.

 

[MikeMl]

Marko, Why don't you just **broken link removed**.

 

[Dr_Doggy]

why not use a battery independent for your starter, then another battery pack set(parallel) for your inverter, and a switch in the cab that will connect it to the car circuit for charging. or better yet put the charger feed line on the ignition so it's connected only when the key is in "on position"