Adding extra batteries

Buying a converter with greater capacity is not going to make much difference, because above 85% state of charge, the acceptance rate is about 12.5 amps. As the bank gets closer to 100% that rate drops. It may take four times longer to get from 85% to 100% than it does to get from 50% to 85%.

The PD 92-series converters all have the charge wizard built in, which is how they differ from the 91-series converters. It may or may not have the external remote box with the blinky light and the mode change button; if there isn't one attached, it can be bought and plugged in. But even without the remote, the charge wizard circuitry is included and active.

This converter should be adequate for any battery bank you could reasonably fit in. Naturally, the larger the battery bank, the longer it takes to charge (at least after a point), and in that case a higher power converter would charge the larger bank more quickly (assuming it's set to output the same voltages). For a single battery or a small bank, the limiting factor may well be the impedance of the battery limiting the charge current, not the power output capability of the converter.

The PD converters are among the best regarded ones available, by the way.

The AMP RATING of a Converter just states how MUCH amp draw it can sustain, NOT installed to provide higher charge rates. For instance, a small 24 foot trailer will usually have a 30 amp converter as the total 12 volt amp draw with everything ON will not be over 30 amps. Larger RV's that have a lot more DC appliances and 12 volt lights will have higher AMP converters. The "charge" by a converter is a extra plus, but the OEM's do not take that into account when spec'ing out an RV. Doug

Does the existing PD converter have the wizard feature? If not I'd certainly upgrade it by adding one.

That converter should adequately handle 2 additional batteries of that size it will take longer to return all batteries to full charge
Here is PD contact info if you want to reach out to them
Progressive Dynamics, Inc.
507 Industrial Road
Marshall, MI 49068 USA

Pho: 269.781.4241
Fax: 269.781.7802

.

The converter is an Inteli Power, model PD9245.

As for why I would only go for such small capacity batteries: The ones I have now is this size, and without modifications, I can't replace these with anything bigger. Then for the extra batteries, I thought you should try to keep the battery banks balanced, and that would mean using the same type.

Or could I use bigger type for the extra batteries?

If I'm going for something bigger, what would be the limit? Will not the converter eventually start struggling when the battery banks get very large?

I agree that 45 amps will charge your battery pack fairly quickly.

I question why you want such small capacity group 24 batteries? They only hold a 'Rated' 85 amps, but in reality will not last as long as a group 31 or group 27 battery. We had a manlift at my work with a group 31 battery, and I upgraded that to a group 5 Trojan battery that was rated at 185 AH at 12 volts. IT was a lot taller, 85 pounds, and a true deep cycle battery.

I guess if you have a height limit, then group 24 is all that will fit, go for it. But you will get just as much capacity with 3 of the group 31 or group 27.

I have a set of 4 golf cart batteries with a total of 440 amp hours at 12 volts, and have a 70 amp charger built into my inverter. It is hooked up with #000 wire (about the size of my thumb) and will charge at 55 amps when the battery bank is about 30% discharged for only a few minutes. After reaching 14.4 volts, the charger slows down a lot, and would only be at 45 amps within 30 minutes - according to my E-Meter. After 1 hour, charge rate will go below 35 amps, that is just how batteries charge. The first hour is really fast, while the second hour is much slower.

Most of the time I let my 415 rated watt solar system charge it. I can put back 120 amp hours per day, but if I used the furnace and watched a lot of TV the night before, I can have the E-Meter reading that there is -130 AH taken from the battery bank, and I might run the generator for 1/2 hour or so in the morning to put back a lot of power quickly, and make it easy for the solar to finish charging it.

Installing a couple of 140 watt solar panels will also help a LOT. Lighter than an expanded battery bank, it will produce all the power that is consumed during the day. Your RV will consume 35 AH daily just to run the CO meter, propane leak detector and refrigerator. This will make a factory pair of batteries go dead in about 3 days.

One of my 120 watt panels will produce about 35 AH daily.

SunElec.com has 140 watt 12 volt nominal panels for $229 a few weeks ago. With aluminum frames. All you will need is a PWM controller, some grey UV rated direct burial wire from Home Depot, and time to install it on your roof.

Good luck,

Fred.

45 amps is fine into 4 batteries. For best recharge you need 14.2 to 14.8 volts. Most converters trickle charge at 13.6 volts. Post what converter you have.

45 amps will be quite adequate. I used to recharge 875 amp-hours of battery with a 40 amp.

Do wire the batteries in a balanced manner.