[rfhendrix]

Ok, I was going to use 12 volt and decided that wasn't such a good idea, then 6 volt (but with quite a bit of extra weight). Now I am considering 8 volt as kind of a compromise. Any thoughts on this? I remember someone saying that the 8 volt batteries were weaker somehow.

 

[rmay635703]

8v are very close to 6v but at a lower capacity. (aka they are about as durable)

Generally how durable a FLA cell is is based on its voltage and capacity.

The lower the voltage and the higher the capacity the more durable a cell tends to be (but not always)

The main reason for this is small cells tend to plug up easily with sediment from daily usage of the battery. 12v are notorious for this type of failure.

Cheers
Ryan May

 

[rfhendrix]

Thanks a lot Ryan.

 

[ngrimm]

I just scored (4) 8 volt Trojans on CL for $20 each. Two are made in 08 and the others in '10 and they test good. My only concern is I have no way to charged them individually since my chargers are 12 volts. I'll have to charge three in series with two 12 volt chargers in series so I don't know how I'll charge the fourth 8 volt. Something to think about if you get 8 volts.

 

[Sunking]

Ok, I was going to use 12 volt and decided that wasn't such a good idea, then 6 volt (but with quite a bit of extra weight). Now I am considering 8 volt as kind of a compromise. Any thoughts on this? I remember someone saying that the 8 volt batteries were weaker somehow.

OK lets bust your first misconception. The key is energy density expressed as wh/kg. What I am driving at is it doesn't make any real significant difference if you use the 6 volt or 8 volt.

The T105 is a 6 volt @ 225 AH or 1350 watt hours.
The T875 is a 8 volt battery @ 170 AH or 1360 watt hours.

Both batteries are the exact same size.
L= 10-3/8 W = 7-1/8 H = 10-7/8
T105 Weight = 62 pounds.
T875 Weight = 64 pounds.

T105 Energy Density = 48.21 wh / kg
T875 Energy Density = 46.89 wh / kg

So in this case the T105 has only a slight advantage.

However there is one difference of note to be made here. The T105 has a higher AH capacity (225 AH), thus a lower internal resistance. What this means is the T105 can deliver higher amounts of current with less voltage drop or SAG. So IMHO you gave up something going with the 8 volt battery.

 

[rfhendrix]

Thanks for your help.

 

[dtbaker]

another consideration MAY be if you have limited space or payload, and still want to get as high a voltage as you can.... my original build I went with 8v because I wanted at least 96v, but no room or suspension to handle 96v worth of 6v.... and I wanted better life than 12v, so went with 8v.

at this point in history though, I would HIGHLY recommend forgetting lead and going to Li cells.

 

[rfhendrix]

another consideration MAY be if you have limited space or payload, and still want to get as high a voltage as you can.... my original build I went with 8v because I wanted at least 96v, but no room or suspension to handle 96v worth of 6v.... and I wanted better life than 12v, so went with 8v.

at this point in history though, I would HIGHLY recommend forgetting lead and going to Li cells.

Well I have two things to consider (not counting the money). One is my 5 mile commute which does not require much range especially since I can charge it at work. The other is my elderly mother lives 100 miles from my house. If I was sure to get at least 100 miles I would seriously consider lithium but I have to be sure before I invest the money.

 

[dtbaker]

a 100 mile range is pushing current battery tech to the max.... I would consider algae-oil diesel if that is really what you need.