Forum Discussion

DrewE's avatar
DrewE
Explorer II
Mar 03, 2015

Sizing a replacement converter

I'm planning on upgrading the old (loud, single-stage) converter in my '98 Coachmen class C to a PD 9200 series unit, and am trying to figure out what size to get. I'll probably be doing a little boondocking from time to time, mostly overnights rather than extended stays, so within reason faster charging would be a positive.

The current house battery is a single 12V battery of uncertain provenance and capacity. I'm thinking I'll be replacing it with a pair of golf cart batteries which I think will fit in the tray, though I haven't yet pulled out the tape measure to verify. (It's inconveniently cold in Vermont to be mucking about with such things.)

Is there any operational difficulty in having a multistage charger that's "too large" for the battery? Intuitively, I would not expect problems, since as I understand it they're basically acting as current-limited constant voltage supplies (albeit with various voltages for the various stages). The charge rate should therefore just be limited to what the battery will accept, correct?

The obvious drawbacks are a higher initial cost for the converter and possibly for larger wiring to for the increased current capacity. I won't be limited by generator capacity.

Currently, I'm leaning towards the 9270 (70A) model. The difference in cost between the 45A, 60A, and 70A models is comparatively nominal. Jumping up to higher capacities is more costly, and would also entail upgrading the AC circuit the converter is on (it's a 15A circuit presently) so I very likely won't go higher.

Thoughts? Suggestions?
  • NinerBikes's avatar
    NinerBikes
    Explorer
    Mar 04, 2015
    What ever charge controller you get, make sure you have enough generator to power it properly without working the generator motor to death. A Honda Eu2000i will handle a 60 amp unit, a 70 amp might be pushing things a bit. Ask for some expert experience here to confirm.
  • tenbear's avatar
    tenbear
    Explorer
    Mar 04, 2015
    smkettner wrote:
    9270 is fine if you pull some #4 wire. If you will be using existing wire that is smaller you may as well stick with 45 or 60 amp.


    SMK makes a good point. The voltage that the converter delivers to the battery is what counts, not the voltage at the converter. With 2 wires, hot and return, of 5' length you will have an appreciable voltage drop at a current of 70A depending on the wire size.
  • Matt_Colie's avatar
    Matt_Colie
    Explorer II
    Mar 03, 2015
    Drew,

    You have lots of complete and good answers.
    I will give a short and simple answer.

    There is no disadvantage to a converter that is larger.
    The battery(s) will only take what they can. Any new multi-stage converter is better than anything that is not.

    Before the depression, I did a lot of boat work. I was forever making happy owners by ripping out old converter/chargers and replacing them with good ones.

    Matt
  • jrnymn7's avatar
    jrnymn7
    Explorer
    Mar 03, 2015
    Sounds like you need a converter that can be manually forced to hold 14.4+ volts during Abs mode, when necessary; like when boondocking. This usually requires a remote pendant, that allows the op to keep the voltage at the bulk/abs threshold setting, rather than it dropping down to the 13.6v "normal" setting. Others here can direct you to the most suitable converter, in that regards.

    As for amperage, I like a C/4 - C/3 rate... so, 25-33 amps for every 100Ah's of bank capacity. A 75 amper on a 225Ah bank would be an example of a C/3 rate, while a 55 amper would be a C/4 rate. (Either of these would be too much for that single 12v.)

    But that's for full time and/or extended boondocking. In your case, a C/6 - C/5 rate should suffice. But, again, get something that can be triggered into holding the higher voltage throughout abs mode, and preferably with temperature compensation.

    For example, using a C/5 rate, i.e; a 45 amper on a 225Ah bank, at sufficient voltage, you could do a 50-80% in about 90 minutes, and a 50-90% in under 2 1/2 hours. You'll know when you're at 90% soc once amps taper down to about 5a for every 100Ah of C (at 14.5v), or about 8a for every 100Ah of C (at 14.8v).
  • time2roll's avatar
    time2roll
    Nomad
    Mar 03, 2015
    9270 is fine if you pull some #4 wire. If you will be using existing wire that is smaller you may as well stick with 45 or 60 amp.
  • DrewE's avatar
    DrewE
    Explorer II
    Mar 03, 2015
    Thank you all for the comments and suggestions. They are very much appreciated. It's good to see that I'm headed in a more or less reasonable direction...or, at the least, not in a completely insane one.

    landyacht318 wrote:
    Powermax also sells the adjustable voltage stageless converters. Nothing Automatic. You can hold Absv for a week if you desire( or forget), or boost voltage in to the mid 15's for an EQ cycle.

    Or set it to 13.2v when your batteries are charged or you have all the time in the world to recharge.

    These adjustables are nice as one can hold the battery manufacturer recommended absorption voltage for as long as required to max out Specific gravity, and hold it higher to get the most out of the time you have to run the generator.


    A manually adjustable unit undoubtedly gives the most control and potentially the best performance, but I'd rather have something I don't need to keep track of quite so much. It's not a lot of work to check things from time to time, I realize, but all the little odd jobs that need attention do start to add up and I'd rather spend my time camping than spend it fiddling with converters and appliances and other such odds and ends...and I'm content to accept the lower performance as a tradeoff.

    grizzzman wrote:
    At best converter in the PD converter section it states that a 14.8 volt converter is coming soon. I would wait for that. 70 amps would be good. Make sure that the converter is mounted close to the batteries with proper wire size and you will be set.


    I wasn't aware of the updated PD converters coming soon; I may have to enquire to see how soon is soon. I certainly won't be going anywhere for a little while at least, since I'm still surrounded by a good bit of white stuff.

    The existing converter location is not terrible; the leads to the battery are around 5 or 6 feet total.

    tenbear wrote:
    The 3 PD 9200 series converters are different sizes. This may or not be important to you. The 9260 can be put in the same space as the Magnetek/Paralax converters while the others are bigger.

    The PD 4600 series is designed to replace the Magnetek/Paralax converters.


    That is a very good point, though it's not a concern for me. The existing converter is a deck mount Magnetek 940 boat anchor in its own (of necessity spacious) compartment.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Mar 03, 2015
    Perhaps the OP ascribes to the KISS principle. The converter has to be a bolt-for-bolt replacement. This limits the field. So does "infrequent" camping. Boosting 14.4V charge AMPS from 50 to 70 might save 15-minutes with his setup. A bolt-in converter with higher bulk limit charge voltage would be far more rational. Bit thrn we return to cost and hassle of trying fit another brand of converter in a brand new unit.
  • BFL13's avatar
    BFL13
    Explorer II
    Mar 03, 2015
    That is what this ugly graph does. You can see the reduction in generator run times for a 50-90 by going to a higher amp charger.

    Diminishing returns. Going from 35 to 55 makes more of a difference than going from 55 to 70. (eyeball values in between) This can be useful when deciding whether to get a more expensive higher amp converter. How many minutes saved is worth it? Only you know what is worth it to you.

  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Mar 03, 2015
    Converter size should be 30% of battery bank C/20 Amp hour capacity

    Example, 100 amp hours (C/20 rate) = 30 amp converter (so a 35 is what you would get cause,, Well, 35 you can get)

    Battery size Type and capacity chart (Recommend upgrade by the way)
    Type is "most common in RV use"

    Group 24 Marine Deep cycle 75
    Group 27 Marine deep cycle 95-100
    Group 29 Marine Deep cycle 100-105
    Group 30 marine Deep Cycle 130

    GC-2 (6V) DEEP CYCLE 210-230 amp hours (You use two in series, voltage goes up (12) Amp hours remain the same) This is the recommended upgrade to if they fit.

    A GC-2 fits a Group 24 tray but is taller

    Total your amp hours (IE: A pair of GC-2s would be perhaps 220, multiply by 0.3 and you get 66 amps. So a 60-70 amp converter is good.
  • tenbear's avatar
    tenbear
    Explorer
    Mar 03, 2015
    The 3 PD 9200 series converters are different sizes. This may or not be important to you. The 9260 can be put in the same space as the Magnetek/Paralax converters while the others are bigger.

    The PD 4600 series is designed to replace the Magnetek/Paralax converters.

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