OK, I have a Morningstar Sunsaver 20a PWM controller. It's not the current generation, which is a 3-stage unit. It's basically a 2-stage without the float stage. It delivers full amps till the target voltage is met, then it tapers the amps. When the batteries are full, it delivers full voltage, say 14.4 at 77F, but very low amps. I've not let it stay connected to see how low the amps go, but let's say they go down to a fraction of an amp for 200 AH of batteries.Given enough time, will this boil the batteries? When I read Morningstar's publications about PWM, it sounds as if, at such low rates of charge, the pulses would be spread out enough to inhibit gassing. I've emailed their tech desk, but I wonder if any of you have experience with same.

Fine for in use. I would not use it for storage.JMHO

Yes, storage type situations are what concern me.

You have a simple, single stage controller. You have a choice with a single stagea) Charge the batteries at a ridiculously slow rate and avoid overchargeb) Charge the batteries at a decently fast rate but then overcharge them (boil).THE CHEAP WAY OUT?Buy a twelve hour wind up timer then give it your best shot at 14.4 volts. Heavy use? Then it'll be dawn till dusk. A voltmeter should be used. The days of non-use will be days of no charging unless you set the charger to float (see below) and bypass the timer.Reset the charge rate to 13.3 for storage and let'r rip without the timer.You COULD get overly clever and wire the timer so when you wind it up it BYPASSES a SILICON DIODE circuit feeding the battery. When the timer runs out, 14.4 volts minus .7 volts for the silicon diode voltage drop = 13.7 volts.Hope This Helps

It lets the voltage drop at night, so you don't get sustained 14+ volts. Yes, 14+ it too high as a 24/7 float even with no amps, except when it is cold out32F - 13.9v15F - 14.2v-5F - 14.4vI think 14.4 all day during daylight would not be good in warmer temps in the long run. Agree with smk. Good for camping, not so good as a maintainerI never did find out what my $13 RJ special does once the batts get charged up. Might be the same deal as that one. (Series type with constant voltage at the high set-point for Absorption while amps taper.)

BFL, the 14.4 is temp compensated, and the controller is mounted right behind the battery (shielded from it). I've seen as high as 14.8 on cool days already. So I'm pretty sure it would be 14.0 or whatever on a hot day. Not sure if this answers your objection, though.It's part of a portable setup, so in reality it won't be used for long term storage. But I do wonder just how long I can get away with it.

PWM controller with no float | Good Sam Community

19 Replies

full_mosey
Explorer
Sep 20, 2013
BFL13 wrote:

Mex says the constant float voltage is better than anything, but you do need shore power for that. So then you might ask, if solar is second best, how much farther off second best is that two stage thing?
I don't know.

I believe Mex is correct. The purpose of float should be to hold the battery at stasis, neither charging nor discharging. In theory, this suspends any chemical reactions and leads to longer life.

Daily solar cycling is a cycle of discharge then recharge. A while back, I proposed to Mex that a nightly draw of 3% and then followed by a daily full solar recharge would give about a 13 year life; he agreed.

At those magnitudes, it doesn't matter.

HTH;
John
full_mosey
Explorer
Sep 20, 2013
westend wrote:
Hey John, from what I've read about the Optima line, they can take a higher float voltage than other VRLA batteries before vent opening occurs.
...
:B

Yes, Optimas are a strange breed. Generally, I won't recommend them for RVing. Too pricey for the AHs. I do get 750CCA from 43.5lbs.

Optima wrote:
Float: 13.2 to 13.8 volts; 1 amp maximum; (indefinite time at lower voltages).

I don't worry about the two stage MS SS-10 not having a third float stage. The second stage tapers Amps well below 100ma, in fact, so low that the Turnigy reads 0.000A and does not accumulate Ahs when topping up in the AM at home.

HTH;
John
full_mosey
Explorer
Sep 20, 2013
IMHO, gassing is not necessary for charging and may even impede charging. Gassing is simple electrolysis where energy is wasted breaking apart water molecules into H and O.

Deka wrote:
If the right pressure (voltage) is used for the temperature, a battery will accept charge at its ideal rate. If too much pressure is used, charge will be forced through the battery faster than it can be stored. Reactions other than the charging reaction occur to transport this current through the battery—mainly gassing. Hydrogen and oxygen are given off faster than the recombination reaction. This raises the pressure until the pressure relief valve opens. The gas lost cannot be replaced. Any VRLA battery will dry out and fail prematurely if it experiences excessive overcharge.

Note: It is the pressure (voltage) that initiates this problem—
a battery can be “over-charged” (damaged by too much voltage)
even though it is not fully “charged.”

With AGMs, stop messing around with high Volts! Do not stir an AGM! Temp-comp means staying below gassing Voltages. Focus more on supplying Amps.

HTH;
John
mena661
Explorer
Sep 19, 2013
full_mosey wrote:
That gassing may not escape the valves. Plus this points out the importance of a temp-comp charging source for AGMs
True and good point!
westend
Explorer
Sep 19, 2013
full_mosey wrote:
mena661 wrote:
westend wrote:

Yes, AGM VRLA batteries are very tolerant but you don't want to float them so high that the valves are constantly opening. If the valves open, you are losing the oxygen and hydrogen that recombines to form the electrolyte.
This is the "conclusion" HiTech came to with his experiments (not saying that's where you got this from). I didn't think they gassed at all unless severely overcharged but a float voltage that's too high does cause gassing.

That gassing may not escape the valves. Plus this points out the importance of a temp-comp charging source for AGMs.

Here is some info re my Optimas under severely hot conditions.

Note that the MS SS-10 lowered the charging Volts to 13.8V when the jumper was set to 14.4V. When I set the jumper to 14.1, the charging volts dropped to 13.5V. That is temp-comp in action. IF there was any gassing, it did not get past the valves. BTW, yesterday I reset the jumper to 14.4V as we are cooling off to the mid 90s in OKC.

HTH;
John
Hey John, from what I've read about the Optima line, they can take a higher float voltage than other VRLA batteries before vent opening occurs.
Agreed on the temp compensation, it's a valuable function.

FWIW, one day I was charging some AGM's with my automotive shop charger. I was nearby and heard a small "pop". Looked over at the charger and saw that I had inadvertently set it on the 40 amp setting. It was charging at 19v and I guess that's over the threshold of vent opening.:B
full_mosey
Explorer
Sep 19, 2013
mena661 wrote:
westend wrote:

Yes, AGM VRLA batteries are very tolerant but you don't want to float them so high that the valves are constantly opening. If the valves open, you are losing the oxygen and hydrogen that recombines to form the electrolyte.
This is the "conclusion" HiTech came to with his experiments (not saying that's where you got this from). I didn't think they gassed at all unless severely overcharged but a float voltage that's too high does cause gassing.

That gassing may not escape the valves. Plus this points out the importance of a temp-comp charging source for AGMs.

Here is some info re my Optimas under severely hot conditions.

Note that the MS SS-10 lowered the charging Volts to 13.8V when the jumper was set to 14.4V. When I set the jumper to 14.1, the charging volts dropped to 13.5V. That is temp-comp in action. IF there was any gassing, it did not get past the valves. BTW, yesterday I reset the jumper to 14.4V as we are cooling off to the mid 90s in OKC.

HTH;
John
mena661
Explorer
Sep 18, 2013
westend wrote:

Yes, AGM VRLA batteries are very tolerant but you don't want to float them so high that the valves are constantly opening. If the valves open, you are losing the oxygen and hydrogen that recombines to form the electrolyte.
This is the "conclusion" HiTech came to with his experiments (not saying that's where you got this from). I didn't think they gassed at all unless severely overcharged but a float voltage that's too high does cause gassing.
westend
Explorer
Sep 18, 2013
mena661 wrote:
full_mosey wrote:
I
With AGMs, there is no water loss at these values due to the built in valves.
Are you sure about that? HiTech detected gassing with his AGMs with too high of a float voltage. Wish he'd come back. He had interesting experiments.

Yeah, where is Jim? I sent off a PM to him a couple of weeks ago and haven't heard back. I also liked his experiments.

Yes, AGM VRLA batteries are very tolerant but you don't want to float them so high that the valves are constantly opening. If the valves open, you are losing the oxygen and hydrogen that recombines to form the electrolyte.
full_mosey
Explorer
Sep 18, 2013
mena661 wrote:
full_mosey wrote:
I
With AGMs, there is no water loss at these values due to the built in valves.
Are you sure about that? HiTech detected gassing with his AGMs with too high of a float voltage. Wish he'd come back. He had interesting experiments.

My recollection is that HiTech was trying to recover some AGMs he acquired used. There is no way an AGM is going to emit any gas under regular charging unless previously abused to the extent that the valves are damaged. There was one previous report of some Lifelines that showed chalking at the terminals and, per the poster, these were replaced 100% by Lifeline due to a defective valve.

I have been 100% AGM since Jan 2009 and have never heard a sound or observed any type of emission from mine.

HTH;
John
mena661
Explorer
Sep 18, 2013
full_mosey wrote:
I
With AGMs, there is no water loss at these values due to the built in valves.
Are you sure about that? HiTech detected gassing with his AGMs with too high of a float voltage. Wish he'd come back. He had interesting experiments.

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PWM controller with no float

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