Advice on PowerMax Boondocker PM3B power converters

georgethe painter · November 02, 2011, 11:37 PM

I am running a '73 Winnebago D20T in stock configuration. I scraped enough money together to purchase a NEW PowerMax PM3B converter to replace the original unit that kind of pooped the bed. They offer amperage ratings from 35 to 100 amp all at prices I can currently afford more or less. 35, 45,60, 75 and 100 amp units are available. Which would be your suggestion in the amperage? I am the king of overkill but I don't want to get too squirrelly when it comes to this. Any advice would be helpful. I am running one 720 cca am battery for the chassis and one for the coach. I am not planning on any elaborate electronic equipment. Thanks in advance...George The Painter

RedneckExpress · November 03, 2011, 01:09 PM

How many batteries do you plan to run George? I'm using the 45 amp model with 3 deep cycles (1 group 27, 2 group 31) and it works rather well with my regular electrical loads.

Also, does your rig use a 15/20 amp service cord (Little household style one) or a big dryer style 30 amp plug?

If you've got the small one, I wouldn't recommend going bigger than the 45 amp due to potential circuit overload if the charger needs to kick up to heavy output (45 amp unit draws 725 watts roughly, a 15 amp rated circuit can only handle 1440 watts continuously and a 20 amp only 1920).

DaveVA78Chieftain · November 03, 2011, 04:30 PM

As long as you are plugged in 24hrs a day, then a 45 will work fine. The typical reason for larger amperage is if you are boondocking and want to run the generator during the day to recharge the battery to replace the energy used overnight. Larger amperage may allow you to recharge faster. Even so, that smart charger knows the battery can only accept so much recharge current so that limits what you can do even if you have a big charger.

Not knowing exactly what your up to, another scenerio is using the rig for daytime transportation and plugged in at night for recharge. Works same as above but your using shore power rather than generator.

Not sure what size battery 720cca is. When talking this subject you use amp-hr ratings. Is it a deep cycle, marine, or starting batter? Is it a group 25, 27, or 29? I know, ya gotta learn the lingo D:oH!

A 45 amp converter is around 750 Watts AC. Thats around 6-7 AC amps (relates to Rednecks AC usage concern about shore power amperage). 60 amp model is around 1000 Watts AC. Thats around 8 AC amps.

Dave

RedneckExpress · November 03, 2011, 05:02 PM

I'm getting a fairly fast recharge rate out of the PM3B units which are a constant current charger. From what I've read, its meant more for charging off a generator, partly why its called "Boondocker" :p.

A 60 would be a better fit for dual bank golf cart configurations (4 6 volt batteries), but if you go too big with too small a battery bank the unit may not go into Bulk/Boost mode (the 14.6 volt output), so there's that trade off as well.

I went up to the 45 amp model over my previous 35 amp model to be sure that the system would actually drop down into float mode even under regular use.

georgethe painter · November 04, 2011, 03:27 PM

My two batteries are group 27 marine. I have the the bigger 30 amp shore cable. For now I am going to be plugged into shore power for the winter while living in it and going through the chassis, rebuilding the brakes, dialing in the motor and of course saving money for a full set of 17.5 tires...oiy-vay $ ! I am planning on doing some boondocking on occasion but mostly I will be plugged in. I have a nice Onan generator with very low usage hours on it so not boondocking seems like a waste of a generater so I'll be hitting the deep woods on the occasional weekends this summer. I seem to be steering towards the 45.

DaveVA78Chieftain · November 04, 2011, 04:15 PM

2 group 27 batterys in parallel provide about 210 amp-hours. You do not want to discharge them past 50% capacity (105 amp-hours) so:
DC Current Daily Total Daily
Appliance Consumption** Use Consumption
------------ ------------ ---------- -------------
Refrigerator 0.25 Amp-hr 18.0 hours 4.5 Amp-hr
Propane Alarm 0.35 Amp-hr 24.0 hours 8.4 Amp-hr
Water Pump 4.00 Amp-hr 0.2 hours 0.8 Amp-hr
CD Player 2.00 Amp-hr 4.0 hours 8.0 Amp-hr
Porch Light 1.80 Amp-hr 3.0 hours 5.4 Amp-hr
Interior Light 1.80 Amp-hr 4.0 hours 7.2 Amp-hr
------------------------------------------------------------
Total DC appliance usage: 34.3 Amp-hr

Total Battery Usage: 76.3 + 34.3 = 110.6 Amp-hr

As you can see you are right on the margin for energy usage. This only applies to boondocking though. Plugged 24/7 the converter is supplying the power and the battery acts more like a filter/accumulator. When recharging after a day of boondocking, the converter is restoring that 110 Amp-hr AND providing for all the loads at the same time. During Bulk/boost (14.6VDC), the converter is acting as a constant current charger until battery voltage reaches a preset level. During Absorbtion stage (approx 13.6VDC) it is acting as a constant voltage charger and drops the current (taper charge) flow based on battery voltage. Simply put, in the last stages of a charge, the battery can only accept just so much current or you will damage the battery. As it approaches 100% the current draw has been dropped to just a few amps. All 3-stage chargers work this way. The float mode reduces voltage to around 13.2VDC at 1-2 amps. You do not want the voltage in float mode to be any higher or it will boil the batteries when nothing else is sucking the current away. A bad battery can cause the charger to go into or stay in absorbtion mode which in time can boil the battery fluid away.

Dave

georgethe painter · November 04, 2011, 04:58 PM

When boondocking I will not be using the reefer, that's what they made ice chests for. My original reefer was unburpable (is that a word) and I have acquired a midsized 110 reefer that will only be used when plugged in to shore power. That being said my battery usage should drop. Being new to this I have to ask the question, with a 45 amp converter and my dual group 27 batteries am I going to within operational parameters. If not should I go with a higher amperage converter than the 45 or will that be too much for my batteries? Depending on how often I boondock after the Hamsteak is completed I may upgrade on the battery bank but that won't be for a while. Would it be better to go with the 60 amp converter or will stick with the 45. When I have the cash I will be running twin group 31 batteries and one group 27 but that will be after the winter when I am boondocking. I would like to just buy this converter once knowing that I will be upgrading batteries but not getting a converter that will fry my current battery bank.

RedneckExpress · November 04, 2011, 08:38 PM

The only possible draw back to more amps in your situation is the PM3B Not going into 14.6 mode when your batteries need a good recharging and only going to 13.6 volts (Slower recharge).

I limited out at 45 amps with my 3 batteries because my loads are lower (And soon to be even lower when I can start converting my light fixtures over to florescent (Existing ceiling units are not a good design for LEDs and newer units are too narrow and will not hide the holes in the ceiling from the old fixtures, all fixtures not on Ceiling have already been converted, furnace only draws 4.6 amps running, etc....).

georgethe painter · November 04, 2011, 09:52 PM

Man my head hurts! Let me get this straight. My final battery array will be one group 27 and two group 31's. I am going to be primarily going to be plugged in to shore power but will want to be able to boondockwhen I get a bug up my bum. In this configuration the 45 amp will work fine whether plugged in or with the generator. The 60 amp model is better suited for a battery array made up of multiple golf cart batteries which I am not planning on doing because of space limitations. With the 60 amp I stand the chance of not going into 14.6 mode for a fast charge. So it is looking like the 45 amp converter is the unit to use with my batteries as it will keep a charge in the batteries with shore power and go into 14.6 mode for a faster charge when using the generator. So the 45 will be the better way to go...correct? "GTP"

DaveVA78Chieftain · November 05, 2011, 01:40 AM

The ability for the converter to go into Bulk mode has nothing to do with converter size. It is directly dependent on battery state-of charge (SOC). As you use energy in the battery during boondocking the battery voltage drops.

Converter detects the 50% SOC when you plug back in and goes into bulk mode (14.6VDC) for 4 hours (per the Powermax PM3 manual). It will then go into Absorption mode (13.6VDC). It will stay in absorption mode until the battery reaches 100% SOC (as shown in table above, battery voltage rises as SOC increases) AND the rig does not need amperage for load support. It will then change to Float mode (13,2VDC). If, in Float mode it, detects a load come on (i.e lights) it will go back into Absorption mode (13.6VDC). If, the converter repetitively cycles back and forth between Bulk and Absorption modes that indicates a defective battery.

There are limits to how fast a battery can be recharged. Exceed those limits and will damage the battery. Just because a charger has the ability to put out a high amperage rate does not mean it will always put out that rate in bulk mode. A 3-stage converter measures the battery SOC and evaluates the battery bank size. It has to do this because if you try to use a charge rate greater than 25% capacity in bulk mode then out gassing (boiling) and excessive battery heating occurs. For a 105 amp-hr battery bank (1 group 27 battery) that means max charge rate is 25 amps in bulk charge mode. 2 group 27 105 amp-hr batteries in parallel (210 amp-hrs) can accept a 50 amp rate of charge in bulk charge mode. You can increase that rate up to 40% (40 amps for a single group 27) if a battery has been discharged below 50% SOC but only until it achieves 50% SOC (13.5VDC). At that point, you have to revert to 25% charge rate in bulk mode until battery voltage reaches 14.4VDC. As you can see, you can use a larger charger on larger banks but a larger charger is wasted on smaller banks but it still adjusts it's output based on SOC. The other thing to remember is if you have say 2 group 27 that allow 50 amp bulk charge you still need to more amps for the coach loads above that 50 amp level during the period of time the bulk mode is ON. However, if not in bulk mode, you are not using 50 amps. You may only be using 15 amps in absorption mode (5 charging; 10 for coach loads). Amperage in absorption mode depends on SOC and coach loads. If battery SOC is 100% then your only supplying coach loads.

Here is a good description of Lead Acid Battery charging principles that all 3 stage chargers are based on: http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery
http://batteryuniversity.com/learn/article/how_to_charge_when_to_charge_table
You will also find some of the same information at 12 Volt side of life http://www.marxrv.com/12volt/12volt.htm (bottom 1/3 of page.

Some of this information is extracted from the books like RV Electrical Systems (Moeller) and Managing 12 Volts (Barre).

Group 31 = approx 120 amp-hr. (25% rate = 30 amps max) 2 Group 31 in parallel = 60 amps max. You could use a 60 amp charger but you will only use that much amperage once in a blue moon if you discharge the batteries to 50% SOC (boondocking). 90% of the time the charger will be in Absorption mode or if rig is laid up Float mode.

Dave

georgethe painter · November 05, 2011, 04:23 AM

I can't believe I was able to understand that! I'm a portrait painter for the love of all things mobile! Thank you all for your input. I understand more about converters now than I knew existed. This is a rather large investment for me right now and I feel confident in my decision. Thanks again for the learning experience...I look forward to more! "GTP"

georgethe painter · November 06, 2011, 01:42 PM

Just ordered my PM3B-45...now I'm staring at my mail box!

Oz · November 07, 2011, 06:51 AM

I know, right? It's like anticipating Christmas morning!

georgethe painter · November 07, 2011, 12:39 PM

From diggin' the Winnie out of it's previous location to sleepin' in it for the first time last night has been a blast! I don't know where to post this but without this site I would have been completely stalled! From coach surfing to having my own operational Winnebago in under a month and just over a thousand dollars...including purchase price and R&R-ing the new roof! Thank you all! "GTP"

ClydesdaleKevin · November 27, 2011, 08:30 PM

Alrighty then...My battery bank, even with the 2 new golf cart batteries replacing the used ones, keep dropping down to about 95 percent on shore power. I can at least charge these ones up to 100% with my new external charger, but I think I should consider one of these Boondocker converters. We are going to be doing a LOT of boondocking this winter once we leave Louisiana!

Okay...so this is our current setup. 4 brand new Interstate golf cart batteries, 2 banks wired to produce 12 volts total. The converter that is in the RV right now is a circa 1989 MagneTek Converter.Battery Charger, so named by its owners manual. It is a deck mount, so replacing it with a new one would be easy, and its even in an easy location to get to. Apparently its not really a smart charger. I read the manual. At full load the converter will put out 12.3 volts. I'm pretty sure its the 40 amp model, although the old sticker on it is hard to read. It has been humming REALLY loud ever since I went with a bigger battery bank. It says max output at no load is 14.1 volts, but doesn't say much about how it charges the batteries. It just says it will charge them, and not overcharge them.

So...I'm thinking I should probably go with one of these Powermax Boondocker converters. I want the generator to be able to charge it quick, and then have clean filtered DC when hooked up to shore power or genny.

Is this the one I should get? Seems to be the best one for our purposes, and the fact that the one we have now won't fully charge the bank on shore power is worrisome. And I don't want to ruin the new batteries we just bought!

I'll be running the fridge off propane while boondocking, but we'll still be running lights, the flat screen LCD TV and DVD player, charging phones and computers, the Fantastic fan, the water pump, the furnace because it gets cold in the desert, and I know the fans on those things eat a lot of battery power, and the power used by the inverter to give the TV/DVD power. So...thats a rough idea of how much battery power we'll be drawing, which is significant since we'll be in the desert and not hooked up to shore power for weeks at a time, living fulltime in the RV. If we have to run the AC it will be off the genny, but that won't be often based on the time of year and past experience.

We have a 45 watt Kyocera solar panel on the roof, with a charge controller. It used to indicate with a green LED that the bank was full when we were running the cheap Walmart batteries. Now the green light only comes on when I hook up the external charger and it reads 100% after a few hours.

I changed nothing but the batteries...end wiring is the same. I don't think the old converter can keep up with it.

That said, should I invest in one of these 3 stage chargers, and more importantly, which amp rating should I get? I'm guessing the 60 amp would be ideal, but just am not sure, and hate to waste money on something I'll have to upgrade later. Should I go higher, or will that be overkill that will eat into my available shore power AC amps? Most of the campgrounds we go to are 15-20 amp AC power outlets.

My mother and stepdad gave us dollars towards our winter vacation for Christmas, and its enough to cover any of the amp ratings of these Boondocker converters. I think it would be money well spent on one of these easily installed deck mounts, but would really like your feedback on which would be the ideal one to get based on what we use.

Thanks!

Kev

RedneckExpress · November 27, 2011, 08:56 PM

With as many batteries as you have, I would go with no less than the 60 amp model, what service is your RV wired for? 20-amp or 30-amp (Big dryer plug vs 3 prong household cord, I have the latter, which is why I limited out at 45amps on the converter).

What is your feed wiring coming from your existing converter to your battery banks? I'm running all 4AWG wire in my system, which allows for the least amount of amps lost and the greatest amount of charge (Including the lines going from the engine compartment and alternator all the way back).

If you're running a microwave, or other large AC Draw (Like an A/C unit) and on a 15 amp circuit doing a heavy recharge from the 60amp converter, you will likely trip the breaker on the pedestal.

If you're hovering at only 12.3 volts, you're harming your bank bad with that Magnetek, 12.3 volts is only 70% of charge (If this is what your batteries are reading in at without load).

ClydesdaleKevin · November 27, 2011, 09:11 PM

We are wired for 30 amps at the cord, regular oldschool trailer plug with 3 prongs. Wires coming out of the current converter are heavy gauge, not sure of what exactly, but thick wires, guessing around 4-6 guage. AC and microwave and all that are only run when the genny is running. The inverter is only hooked up to the TV/DVD player...and I can run an extension cord to it for running drills and saws and whatnot, which I won't be doing on vacation when I can avoid it!

Batteries are reading around 12.9-13.1 volts on shore power, 95% according to my external charger...but on shore power with a good converter they should be reading 100% or close to it. 12.3 is what the converter manual says the converter will put out on full load, while at no load it puts out 14.1. Not a smart charger apparently.

I'm thinking 60 amps will be ideal, but don't want to under-do it, or over-do it and trip breakers while on shore power.

Kev

DaveVA78Chieftain · November 27, 2011, 10:49 PM

Upgradding to a 3 stage would be the best thing to do. I am guessing each 6 volt battery is around 220AH which will give you around 440AH total. Of that 440AH, to avoid excessive battery sterss, you ONLY want to draw it down to 50% which is only 220AH. Please understand that 45 Watt solar is nothing more than a battery tender; no where big enough to add much charge. What you really need to do first is do a AC and a DC usage evaluation.
Example:
AC loads:
Converter (60 amp) = 8 amps (aprox 1000watts)
AC = 15 amps
Computer/Misc = 5 amps
Total = 28 amps from the 30 amp service
You would have to turn the AC off to run the Microwave.

For DC, the example I used before:
DC Current Daily Total Daily
Appliance Consumption** Use Consumption
------------ ------------ ---------- -------------
Refrigerator 0.25 Amp-hr 18.0 hours 4.5 Amp-hr
Propane Alarm 0.35 Amp-hr 24.0 hours 8.4 Amp-hr
Water Pump 4.00 Amp-hr 0.2 hours 0.8 Amp-hr
CD Player 2.00 Amp-hr 4.0 hours 8.0 Amp-hr
Porch Light 1.80 Amp-hr 3.0 hours 5.4 Amp-hr
Interior Light 1.80 Amp-hr 4.0 hours 7.2 Amp-hr
------------------------------------------------------------
Total DC appliance usage: 34.3 Amp-hr

Total Battery Usage: 76.3 + 34.3 = 110.6 Amp-hr

By doing a inventory you can determine what your real needs are.
At a max 25% charge rate, your large 440AH battery bank can accept up to a 110 amp bulk rate so you can go larger if you want. The 60 might even be stressed on a daily boondocking situation depending on your AH usage. You will not know unless you figure out what your max daily need will be.
Remember, the amount of charging capability will be reduced by the amount of current DC amperage usage. If the furnace is on and drawing 11 amps and the inverter is drawing say 30 amps (300 watt inverter), a 60 amp converter/charger will only be able to provide 19 amps of charge. Point is you have to think through the whole story.

Dave

ClydesdaleKevin · November 28, 2011, 07:26 AM

So, if I go larger, then will it cut into my available shore power amps? Its not much of a difference in cost for these things. As far as determining how much power we'll use exactly, that is a hard one to nail down. Ya see, if it was just me, I could run one light at a time, turn it off when turning on another, etc. The wifey is the wildcard. She's the kind of gal who likes every light in the house on. She is getting better about turning them off, but its going to be a learning process for her...and there is a reason we are happily married: neither one of us orders or forces the other to do something, or nag too much about what needs to get done. She said she'll conserve power, but she'll probably forget...lol!

The inverter is a Coleman, 2500 continuous, 3000 watt peak. The way I have it wired in, its not hooked directly into the system. Its mounted inside one of the dinette benches, with an extension cord running back under the cabinetry to the TV/DVD player in the bedroom, a 34" flatscreen LCD model with built in DVD player hanging on the wall. When the TV isn't being used, the inverter gets shut off. So its not running continuous....BUT, Patti likes to sleep with the TV on. She's good about setting the sleep timer on the TV so it shuts off after 2 hours, but that means the inverter is still running with little load until I get up a shut it off in the morning...AFTER she watches a couple early morning programs.

That said, lets figure it out.

DC=

Fridge-6 amp hours...running 24 hours
water pump-4 amp hours
lights-14 amp hours
inverter-8 amp hours
tv/puter/chargers off inverter-8 amp hours

That is figuring high, at a total of 40 amp hrs

So if the inverter is drawing 30 plus amps, and we are running the furnace at the same time, then you are saying that available amps from the 60 amp converter would only be 19 amps leftover for charging...

So...I'm going back to the Powermax website to figure this out.

Kev

ClydesdaleKevin · November 28, 2011, 07:46 AM

Alright...this is what I've sort of come up with, estimating power usage.

If I turn off every or almost every DC appliance while the genny is running, I could get away with the 60 amp. It also comes in 75 amp and 100 amp.

That said, if I don't want to worry about what DC appliances are running during a charge phase with the genny running, then I could easily go for the 75 or the 100 amp model.

Since the battery bank is big enough to safely handle the 100 amp model, then that appears to be the logical choice, especially if I decide to go solar next year and add 2 more batteries to the bank, for a total of 6 golf cart batteries.

Now...

Here is the question, since none of the models on the website tell you how much AC amps they draw on shore power:

Is there a big difference in the amount of AC amps a 60 amp converter will draw from shore power, versus the 75 or 100 amp models?

This is where compromize might have to come into the picture. As said before, we rarely stay at a campground that has true 30 amp service. Most of them that we stay at are 20 amps. Only one, Kentucky, has true 30 amps.

We always shut down the AC to run the microwave, etc, so that isn't an issue.

I'll get the biggest one, but I don't want the breakers to trip at the campgrounds just running my AC because I bought too big a converter.

So is there a big difference in AC amp draw?

Kev

ClydesdaleKevin · November 28, 2011, 08:16 AM

Alright...it doesn't appear that there is too big a difference in shore power amp draw from one model to the next, so I went ahead and ordered the 100 amp model. Should be at the Louisiana Renfaire when we get there in a couple of days.

We aren't leaving here till tomorrow morning, since a big storm is coming right at us today up I-10. Looks like another day in sis's driveway.

Kev

DaveVA78Chieftain · November 28, 2011, 10:04 AM

For reference:
Using a normal mode (Absorbtion) value of 13.6VDC and an efficency of 80%:
13.6VDC x 100 amps x 1.2 (efficency) = 1632 Watts
1632 Watts / 120VAC = 13.6 AC Amps (max converter load)
(That is formula tracks very close with my 60 amp Progressive Dynamics PD-9260 model)

Like shown in the graph in the Powermax Boondocker installation manual (http://www.bestconverter.com/assets/images/Powermax/PM3B%20Manual.pdf), the converter will put out max amperage in bulk stage mode until the charging voltage value required to sustain max amperage reaches 14.6 VDC. When that point is reached (approximately 80% SOC) it changes to Absorbtion mode (13.6VDC) and ramps current down until a balance is reached where the battery is charged and the converter is mainily suppling just the normal system loads (fridge, water pump, inverter, etc.). It WILL NOT go into float mode until all external loads (fridge, water pump, inverter, etc.) are shut down (storage mode). Only real way of knowing what is going on is with amp meter connected in series with the battery such that it monitors all current going in/out of the battery.
Please understand that that big 2500W inverter can draw around 230 amps continious at full load from the battery (275 amps at 3000 Watts peak) which is larger than even the 100 amp Converter can handle. Just trying to put things into perspective.

It may also help to know, that if you draw 10 amps from the battery for 10 hours (100 AH) it will take 125% to restore that 100AH (i.e 125AH). In other words, if charging at 10 amps it would take 12.5 hours to restore that 100AH. Just the nature of batteries.

While to some degree this all sounds confusing it all follows basic ohms law (I x R = V). In our case, as the battery SOC is increased, the battery resistance (R) increases. In bulk mode charge, in order to maintain a steady amperage rate the charger voltage must be increased as the resistance of the battery increases due to increased SOC (R increase). However, getting the voltage to high (above 15VDC) will damage the battery and create excessive boiling. So, the comprimise is, when battery votage reaches 14.6VDC (approx 80% SOC) change to absorbtion mode (13.6VDC). The lower voltage will not create excessive battery water boil off and as the battery SOC increases (ergo continued battery R increase) the current (I) is ramped down (V remains steady at 13.6VDC) to compensate until battery is charged and the converter is mainly just supporting system loads. You just cannot get away from the basic Ohms law component of the situation. Your bigger battery bank allowed the overall R value to decrease so you could use a higher amperage (I) converter.

Dave

Oh, BTW I too hold the Dolphins

I am still working in the submarine field supporting the main Sonar Systems on SSN's, SSGN's and to a lesser degree, SSBN's.

ClydesdaleKevin · November 28, 2011, 10:35 AM

Thanks for all the info, Dave. I'm pretty sure I made the right decision. The crummy Walmart batteries supported the inverter and TV setup as we use it before the battery upgrade, so I'm pretty confident that the 100 amp model will be ideal and not be overkill. Probably could have comfortably used the 75 or even the 60, but am more comfortable with my decision to get the 100 amp model.

Funny, but you would think all this would come naturally, since I was an ET/Nav on 688s, but I started out way back as a QM, and didn't get off the charts much to learn the electrical side of things when they combined our rate with the ICs. I learned just enough to pass the exams and make rate and pass the boards, but just barely. Mostly I was plottin' dots.

Thus the reason I'm in Saint Marys, GA right now. My sis's hubby is a Senior about to make Master. He took a Cob Job back in Groton, so he flies home when he can. Sis stays here cuz the kids are in a very good school.

To my fellow Bubblehead!

Cheers!

Kev

RedneckExpress · November 28, 2011, 01:51 PM

Actually Dave, the Powermax will go into float mode even with loads, mine stays in float even with regular use once the batteries are full up. I tested this just recently when our power kept going out. I consumed my batteries down to around 80% and she popped up to 13.6v till they charged back up then dropped back to 13.22 afterwards and has stayed there.

Kevin, you may want to consider upgrading to 2 AWG (Which I believe is as big as the lug attachments on the Powermax will take) from your converter to your batteries to help improve charging efficiency.

Look on the wrapper of the wire to see if you can find the producers print that states the size and rating info.

DaveVA78Chieftain · November 28, 2011, 03:56 PM

QuoteActually Dave, the Powermax will go into float mode even with loads, mine stays in float even with regular use once the batteries are full up. I tested this just recently when our power kept going out. I consumed my batteries down to around 80% and she popped up to 13.6v till they charged back up then dropped back to 13.22 afterwards and has stayed there.

Actually thats a good thing. One problem in the old days was that the converter constantly ran at 13.6/13.8 VDC for charging. At that level the battery was boiling or exhibited higher water evaporation. 13.2VDC is the best to maintain the battery without the higher risk of water burn off. There is more than one way to skin this cat and waiting till battery voltage is at 80% SOC before switching back to absorbtion stage is one way of doing it.

Dave