RC and Amphr Rating ? w 24v System

[tahoejag]

Fellow Boaters and Battery Experts....Battery is a Interstate SRM-29 rated at RC capacity 210 min = 3.5 hr @25 amps (hope thats correct me saying that). I have two of them...hence 24 volt system hooked to MK Terrova 80#.

My question...Is the RC capacity DOUBLED being I have 2 batteries? i.e. last for 7 hrs @ 25 amps?

Also...may be a bit confusing, but I have a 2 bank charger (on-demand) 5/5. On the charger it states Output = 100 amps in 10 hours. Trying to get estimate of how long it would take to charge compared to amps being used and replaced by the charger on a 24 volt system (if that has anything to do with it).

p.s. - I get into this tech sh*t and love to learn! Thanks in advance for the input!

 

[dwparker99]

Re: RC and Amphr Rating ? w 24v System

When you add a second battery to get 24v you will double the RC capacity but in your example, you will not get 7 hrs @ 25 amps. Since both batteries are outputting 25 amps you will get 3.5 hrs. Since you doubled the voltage and kept the current the same, you will get double the work output from the TM.

How long it will take a charger to charge a battery is difficult , if not impossible, to calculate. Charger output is rated at max output but in reality a charger very seldom runs at max output. From my experience, a battery has to be below 65% State of Charge (SOC) for the charger to output max amps. For instance, my onboard Noco Gen3 with 10 amps per bank output will start charging at 7.2 amps when the battery is at ~75% SOC. Determining how long it takes your charger to charge a battery at a certain discharge level is best determined by experience.

One caution about charging is don't assume that just because the green light comes on that the battery is 100% charged. Some charger turn the light on when the battery is 90-95% percent charged and continue to charge for sometime afterwards.

 

[Silvertip]

Re: RC and Amphr Rating ? w 24v System

When you add a second battery to get 24v you will double the RC capacity but in your example, you will not get 7 hrs @ 25 amps. Since both batteries are outputting 25 amps you will get 3.5 hrs. Since you doubled the voltage and kept the current the same, you will get double the work output from the TM.

Untrue! You do not double the reserve capacity in a series system. That happens in a parallel system. Two batteries in a series system provide double the voltage but the reserve capacity remains (in this case) at 210 minutes (not 420). An 80# Terrova at worst case can draw 56 amps @ 24 volts. That current draw is a little over double the battery rating (210 minutes @ 25 amps). That means run time is cut in half since you are drawing twice as much as the rating. Therefore run time is 105 minutes "worst case" or a little over 1-1/2 hours. Rarely would that worst case scenario ever occur so realistically you could expect 2-1/2 to 3 hours of use at a more moderate speed and frequent start/stop operation. There are no current draw charts that detail the full range of current draw for various speeds because of the variables, but if you assume 1/2 speed results in 1/2 the current draw (28 amps in this example) then the 210 minutes (3.5 hours) run time is very possible. As for charging, let the charger do it's job. It will tell you when it has gone into "float/maint" mode.

 

[tahoejag]

Re: RC and Amphr Rating ? w 24v System

If I understand this right....two 12v batteries in series will give me 24v, but will not double the RC. I have pulled up some more info on the battery as to the RC for one battery.

RC = 210 min.
Hrs @ ampere load - 5 amps=21 15 amps=6.4 25 amps=3.4

Understanding that the TM will pull various amps and 56 amps being the max. Lets just say that it is pulling a steady 25 amps at 24v, according to the rating of the battery, they will last 3.4 hours and not 6.8 hours, because the RC is not doubled in series. The only thing that is doubled is the voltage.....12v to 24v. Correct?

As for the charging, i understand that depending on the state of charge, depends on how long it will take to replenish the amperes used back into the battery, as the charger is 2 bank 5/5 and says output of 100 amps at 10 hours. For there have been days it took one day to charge (green light) and other times it took 3 days to see green light. (Promariner tournament 100 charger) which I assume is a decent charger.

 

[Silvertip]

Re: RC and Amphr Rating ? w 24v System

That's correct. two 12 volt batteries in parallel doubles the RC but the voltage is still 12 volts. Two 12 volt batteries in series doubles the voltage but the RC remains the same as whatever the single battery capacity is.

 

[tahoejag]

Re: RC and Amphr Rating ? w 24v System

That's correct. two 12 volt batteries in parallel doubles the RC but the voltage is still 12 volts. Two 12 volt batteries in series doubles the voltage but the RC remains the same as whatever the single battery capacity is.

Thanks! ....question answered.