Qn about gel batteries as tank battery

**SteveC** · 10-10-2004, 03:55 PM

I went out yesterday and bought a split relay charger - the sort used to charge an RV second battery when the engine is running and that prevents the main battery from discharging.

I want to use a smallish gell battery as the second battery and connect it to the split relay charger so that it acts like a tank battery but also so that I can leave the PC running and start the car without it rebooting the PC.

It's cheaper than spending hundreds of bucks on an Opus

Is this a safe thing to do - can I use a small (probably a 7Ah) 12V gell battery in this way or is there a danger of overcharging etc. Don't know much about gells and I don't have room for a full size lead acid battery anywhere.

Thanks

Steve

**e_z_street** · 10-10-2004, 06:39 PM

Please post more information about the charger you bought.

**carpcnoobie** · 10-10-2004, 06:54 PM

Are you trying to do like in this thread?

you dont necessarily need a voltage regulated PSU

**SteveC** · 10-11-2004, 01:10 AM

The Isolator details are at http://www.jcwhitney.com/autoparts/P...X/appId-385764

Yes I'm kinda following that thread (which got a bit OT) but they are now talking about diodes etc whereas I just bought a $30 isolator. The spec talks about having dissimilar batteries but seems to refer to them as lead acids so not sure what using a sealed small gel battery will do.

Steve

**hcker2000** · 10-11-2004, 05:08 AM

Well which ever terminal is suposed to hook to the 2ndary batter you sould check to make sure its not geting to many volts. I would check the battery specs to see what the carging voltiage is as well. If thats what your isolator puts out then you should be good.

**carpcnoobie** · 10-11-2004, 06:19 AM

Thanks for the link. I'm following this as well. Exploring the many different powering options. Right now I have a 400w inverter on the main car battery. Wouldn't mind a small aux. battery. Seems more flexible then worrying about killing the main battery.

**SteveC** · 10-11-2004, 11:54 AM

NP carpcnoobie

I started off with a 400W invertor and a standard ATX PSU but then investigated other options. The Opus is very nice but very expensive and when I purchased the Epia+case combo it came with a DC-DC PSU built in but it drops out when cranking the engine. The cheapest option seems therefore to be a small gel battery with constant charge from the engine using a $30 isolator. I have room to mount the isolator next to the main battery under the hood and can then run a charging lead back to the gel and then onto the PC - the spec of the DC-DC PSU in the PC seems to be about 11.5V - 15.5V so that should work just fine and allow me to stop and start the car without having to hibernate or reboot.

I was just concerned on how the gel battery would respond to 14.4 v so I'll have to investigate this further.

Steve

**fordman** · 10-11-2004, 12:21 PM

Dont worry about overcharging a gell battery. It acts like a regular lead acid battery.
If you go for a orbital battery then make sure it dosent charge over 14.5 volts otherwise you will only get 2 months life.

**justICE** · 10-12-2004, 12:15 AM

Get one of these. They do not have a maximum current as long as you stay within the Voltage range.

**VanMan69** · 10-12-2004, 12:36 AM

I don't think there should be any problems with this setup. My setup uses an isolator and three batteries: single DieHard under hood isolated from two Yellow Tops in the back (Yellow Tops wired in parallel).

Another neat advantage is that you don't need your key to start the computer, but you will need a separate switch to turn it on and off (unless you get some kind of controller hooked to accessory. don't know if there are turn-on controllers like there are shut-down controllers) Depending on how you wire everything, though, you'd still need a key to turn on the radio (mine's wired with a switch to turn on without the key).

Keep in mind that this is a separate issue than that related to an Opus. Even with the gel cell, you need to get the 12V into the computer by either inverter or 12V PSU (Opus). The Opus can also supply the start-up/shut-down control. I think the Opus can also survive a crank. I don't have an Opus so can't vouch for sure.

The gel cell doesn't replace the Opus, it's just a beefier version of the small tank circuits some people use.