Battery type question for all the battery experts

[oldmansax]

The PT40 I am working on came from the factory with the 12 volt coach & house electrical systems combined. There was only one set of batteries. The best I can figure from the original specification is the battery bank was 440 amp/hours. The original design included a battery disconnect that isolated some of the coach systems while camping. There was no way originally to completely disconnect all the batteries from the system. To further complicate matters, the PO tapped into the system for various after market accessories and some repairs without regard for where in the system the accessory might belong. Eventually I am going to separate the systems, but, for now, I need to get it on the road.

I have already read a considerable amount about battery types & best practices. I know I should be using starter type batteries for the coach & deep cycle or AGM type for the house system. That is not possible as both systems are combined. It is not recommended to mix battery types in one bank & would be useless I think.

The basic question is: What type of batteries should I use?  A set of start type batteries? A set of deep cycle? A set of AGMs ( if I can afford them!  )

The original bank was 440 amp/hours so I can assume a start bank of that size would work; BUT, the Wanderlodge has so many phantom loads most owners only get a day or two out of the batteries before they are dead. I would like to do better if possible. If I use deep cycle or AGM batteries, do I need to make the bank larger to compensate for the starting load?

Also, does anyone know the amp draw of a 6V92T while starting in cold (+20F) weather? The PO installed a Link 200 to monitor the batteries. It uses a shunt on the ground side to monitor amp draw. The shunt is rated for 500 amps. I don't think that is big enough but I don't know. I know I can ground the batteries directly to the starter but that nullifies the amp draw function on the shunt. If the start current is more than 500 amps, can I switch the shunt to the load (positive) side? That way I can bypass the shunt with the starting load by running a cable from the batteries directly to the starter. I know I would probably have to reverse the wires so the Link 200 would read correctly.

What say you?

TOM

[HighTechRedneck]

Definitely a questionable system with a lot of risk of being stuck without enough power to start the engine.  Sure seems like it would be worth the effort to separate the battery systems.  But if that is simply not an option for you at this time, I would suggest Marine Batteries.  They are a compromise between Deep Cycle and starting batteries.  Going with either regular start batteries or full deep cycle batteries in your situation would result in short battery life and less that optimum functionality.

As for starter current, I recall that Clifford recently (last few days) posted the starter current for a particular bus in a reply to a thread.  It was way above 500A.

[bevans6]

The spec for the stalled current of the start in my bus is 500 amps, but it's a 24 volt starter.  Logic suggests that the locked rotor current of a 12 volt starter would be a lot higher than that.  If I was looking for dual purpose batteries that had 440 ah rating, I would probably look at marine 8D's, a pair of them.

Brian

[white-eagle]

how well does the bus start?  do you have a block heater?  My 8v92 cranks about 2 sec on a 60 or above day.  it would probably crank about 5 sec, then another 5, then another 5 with ether, if i didn't use the block heater.  with a block heater, it cranks just like it was 60 deg out.  so i don't need much juice to turn it for very long.

i have 3 31's for starting.  i have 6 GC for house.  they are tied together for charging, and if i forget to unhitch them, for starting.  so far, i forget to disconnect the GC for starting most of the time with no obvious issues.

i don't like 8d's for anything.  they are heavy to move.  to get high crank, they increase the number of plates, make them thin, and reduce the amount of acid.  so if you get them for cranking, they'll suck for house use.

i like the 31's or GC's.  if you could somewhat separate them, then i would do them similar to what i did.  if not, you are only using the cranking for a short time and 6 GC in parallel/series should have a lot of CC power, if the engine block is warm.  if you plan to boondock and use the house batteries, i'd got for GC because that is where you will need most use and like i said, they should provide easy start power if you can warm the engine.  even without a warm engine, a shot (and just a shot) of ether should help start it up quick without melting the GC's.

imho.  hth. call if you'd like to discuss.  i may not be an expert, but i have seen what goes into a battery first hand after working in a battery factory.