What size converter do I need?

[HippieFemm]

Sent: 7/9/2003

Can some of you electrical wizards explain to me how I choose what amp converter I need to get? I have been looking at those 9100 series on the progressive dynamics site with the charge wizard as previously suggested. It comes in 40 amp and 55 amp. Since electrical systems are REALLY not my strong suit I don't want to cause further issues to troubleshoot later. I have a 1970 Chieftain w/ 4.7kw Kohler generator and use 30 amp shore power. Thanks for any info, I don't want to burn the anything up....... I fear fire.

[DaveVA78Chieftain]

Sent: 7/10/2003

Unless I misunderstand the way they hookup, understanding proper electronic converter selection is requires an understanding of how the original linear converter was hooked up vs how the electronic converters are hooked up.  70's era Winnie's used a linear converter that had a separate battery charge circuit.   The main portion of the converter supported all the 12V electrical loads.   The battery itself was isolated from the loads via a large relay when the converter was running.  Installation of a electronic converter requires you to rewire this so that it feeds the battery and the 12V electrical loads are feed directly from the battery connection.  You still need to keep the fuse panel in the load circuit though.  This approach is basically the same setup as the alternator (converter off).  The alternator or electronic converter would be performing a battery recharge, it would also be supplying all electrical loads.  So, part of the available amperage is being used to charge the battery while the rest is handling the 12VDC house loads.  The more loads there are, the less current there is available for battery recharge.   Converter size therefore depends on:
1.  How often would you be in a boondocking situation (battery only mode) such that you would need frequent heavy charging rates.
2.  Are you running an inverter and is it being used a lot such that you drain the battery frequently?
3.   Do you do winter camping a lot such that the furnace is being used a lot?  The blower motor  would draw a lot of 12V power.
While there are even more issues related to how much power do you expect to consume (many web sites/books available to help define that) it is defining the amount of need which has to come first.  Then you need to estimate how long you will have 110VAC available for battery recharge.  If you expect to typically have 110VAC available for a long period, then a smaller converter is ok.  If you need quick charge then a larger version is needed.  It's about achieving a balance based on what your typical RV lifestyle requirements are.  Many can get by with a smaller converter because they do not boondock very often and have 110VAC campground power typically available.  Others need a larger converter because they need the quick high amperage charge rate (say generator driven) and usually add solar charging to assist.   No, it will not hurt anything (other than your pocketbook) to get the larger one.  Just remember, the electronic converter does require you to rewire the "old" implementation because that battery/converter relay is no longer required.

Dave