Lowest Safe Instantaneous Voltage Under Load

[MsNomer]

I have two 100Ah Trojan AGMs charged by 300W solar with Trimetric SC-2030 controller, NOCO Genius charger when on shore power, and occasionally the alternator, so they spend most of their life fully topped off--and I do mean "fully" with a profile recommended to me by Trojan in person. The system is monitored by a Trimetric TM-2030.

When I run the 600W microwave--never more than 2 minutes at a time--through the Raptor 1500W inverter, there is a 75A draw. Voltage dances like a banshee, usually in the 12.1 - 12.4 range with an occasional instantaneous blip to 11.7 - 11.9. Is this normal? Where is the point at which I should be concerned?

[booster]

Originally Posted by MsNomer

I have two 100Ah Trojan AGMs charged by 300W solar with Trimetric SC-2030 controller, NOCO Genius charger when on shore power, and occasionally the alternator, so they spend most of their life fully topped off--and I do mean "fully" with a profile recommended to me by Trojan in person. The system is monitored by a Trimetric TM-2030.

When I run the 600W microwave--never more than 2 minutes at a time--through the Raptor 1500W inverter, there is a 75A draw. Voltage dances like a banshee, usually in the 12.1 - 12.4 range with an occasional instantaneous blip to 11.7 - 11.9. Is this normal? Where is the point at which I should be concerned?

That is very normal, actually quite good. Many inverters will allow as low as 10.5 volts. I think we have our low limit to 11.5v. We have 440ah of Lifeline AGMs and a 750 watt microwave.

How are you determining that the batteries are totally full? The Trimetric will tell you, but it has to be programmed to the right settings, including all the ones that determine when it lights the fully charged indicator. The Trimetric solar controller can be programmed to do the absorption to float transition at the right point, based on the amps to the battery, but the NOCO appears to be normal "smart" charger that uses an algorithm to do that transition, which is not likely going to be very accurate. Charging off the alternator is almost always uncontrolled. Normally, the smart chargers will leave the batteries undercharged by some amount, and the alternator will either overcharge or undercharge based on how full you were when you started the drive and how long you drove.

The good news is that you can find out for sure very quickly. If Trojan didn't give you what the "float transition amps" should be (that is the amps accepted to the batteries when they are totally full), you should ask them for that number. It will probably be in the .5-1.0% of capacity range. When the Trimetric shows the charging has tapered to that many amps, you should be going to float or you will be overcharging. If setup right, the Trimetric will keep the solar from overcharging, and also give you an accurate fully charged reading, but the other sources won't do that, or assure you get full. IMO, driving with already full batteries is one of the most common overcharge causes in our RVs, and can definitely shorten battery life. The Trimetric if setup correctly will be very good for telling if you are full, but it will not accurately tell you if you are overcharging, which can be even more damaging than undercharging, I think. You only indication on the Trimetric would be if your recovered charge % goes to more than about 115% on any given recharge cycle before going to float, but it is not a very accurate test, just an indicator of if you are going into overcharge.

[mojoman]

I believe it has been discussed before concerning adding a small lithium battery set up to boost voltage during surges. Same way a capacitor works except for long duration. A simple setup would only involve a small lithium battery and a boost switch or a voltage triggered solenoid if you want to get fancy. I have started a car with a dead battery with a lithium battery the size of my fist.

[markopolo]

Originally Posted by MsNomer

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When I run the 600W microwave--never more than 2 minutes at a time--through the Raptor 1500W inverter, there is a 75A draw. Voltage dances like a banshee, usually in the 12.1 - 12.4 range with an occasional instantaneous blip to 11.7 - 11.9. Is this normal? Where is the point at which I should be concerned?

My setup for comparison:

600W cooking power / 900W power consumption microwave oven
1500W PSW Samlex inverter
Mixed lot of older batteries totaling around 390AH

Starting with fully charged batteries, the voltage shown by the Trimetric quickly drops to 12.0V during the first 30 seconds and then holds steady there. 85 amps being drawn from batteries shown by Trimetric. The amps slowly but continually increase; 84.5. 84.6, ..... 85.1, 85.2 etc. It takes a minute or so for the voltage to recover to 12.7V after the microwave oven stops with the van out of the sun so no solar input.

85A x 12V = 1020W That seems right to me. It indicates approximately 10% inefficiencies/losses to produce the full 900W for the 600W microwave oven.

Edit to add: Just a guess - the voltage shown in your system might jump around if solar input was supporting part of the load.

[MsNomer]

All this is good to know. Thanks.

I feel pretty confident that when the meter says they are full, they are full. I have set all the parameters in the meter according to my conversation with Trojan, including the 107% push at the end. It is a slow push from 99 to 100%.

The meter controls the solar, too, so I feel good about that. The NOCO charger is indeed a black box, but it is the one the Trojan rep recommended, and as I watch the meter, I don't see appreciable difference between solar and NOCO. We have to use shore power in our completely shaded driveway.

I agree the alternator is inferior. We have had it disconnected since we added solar. Boondocked with shade/clouds would be its only application. In that situation, it would undercharge, then solar would finish them off.

Edit to add: the NOCO rep was specific that the charger should go to 14.8v and have the log tail at the end. He was concerned that the charge be complete.

[booster]

Originally Posted by MsNomer

All this is good to know. Thanks.

I feel pretty confident that when the meter says they are full, they are full. I have set all the parameters in the meter according to my conversation with Trojan, including the 107% push at the end. It is a slow push from 99 to 100%.

The meter controls the solar, too, so I feel good about that. The NOCO charger is indeed a black box, but it is the one the Trojan rep recommended, and as I watch the meter, I don't see appreciable difference between solar and NOCO. We have to use shore power in our completely shaded driveway.

I agree the alternator is inferior. We have had it disconnected since we added solar. Boondocked with shade/clouds would be its only application. In that situation, it would undercharge, then solar would finish them off.

Edit to add: the NOCO rep was specific that the charger should go to 14.8v and have the log tail at the end. He was concerned that the charge be complete.

Good information. Did Trojan give you a transition amps to float? It is important because the Trimetric needs that to accurately give a full reading when the batteries are really full. The 107% is a guess in most cases because it is dependent on how deep the discharge was and can vary a lot. Ours can be anywhere from about 7% to about 13%. What do you have the full battery amps set in the Trimetric? That is the critical part of it all, and the only thing that will be truly consistent and accurate. If that is correct, you can watch the Trimetric when your shore charger is getting near the end of the charge to see when it lights the full light, plus you can watch the amps and volts to make sure they meet the transition amps that Trojan wants. It would be very interesting to actually see what the amps are when the shore charger goes to float at a couple of different discharge depths. I have never seen a charger that wasn't either over or under on at least most recharges. It would be really nice if someone came up with one that did a better job. The 14.8v tail at the end is getting to be more common for the AGM batteries. It appears to really be a mini conditioning cycle that they do every cycle, probably because so many batteries get drawn deep and then undercharged on the recharge, causing capacity walkdown. It would also be interesting to see what amps it runs in that stage, and what Trojan recommends, as I don't think that charger is capable of constant current charging.

[MsNomer]

Mojo, I would like to know more about that lithium setup. I can't afford to switch to lithium, but I might be able to afford that.

[booster]

I found this on the Trojan site. Charge parameters and a profile graph that also specifies the amps at float transition. It is the same % that Lifeline recommends at c/200 or .5%. That would put your Trimetric setting at 1.0 amp for your 200ah of battery.

[MsNomer]

It's been a while and I don't remember what these mean, but these are the notes I copied to my manual:



Like I said, they came from a Trojan rep directly. I certainly appreciate your review.

We leave for the bottom of the Grand Canyon in a couple of days, so I'm busy making sure I don't forget anything. The van has certainly spoiled me that way.

[booster]

P2 is the one that tells it when to light the charged light by the amp reading, and it is at .5%, so that is fine. It should also control the charging out of the solar to end it at the proper time. I am a little surprised at the 14.7v for the absorption voltage, as it is right at the high limit of their specs, but that is probably also due to their fear of chronic undercharging. Very similar to the charger people adding the finishing high voltage stage.

You should be good with the solar, but if you get a chance, you may want to look at the shore charger running sometime just to see. You can watch the amps on the Trimetric going into the batteries, and see it it gets to the 1 amp, lights the charged light, and then goes to float within a short time (voltage will drop to 13.2-13.5ish volts). If it stays at absorption voltage more than 1/2 hour our so, you may need to be concerned, especially at the higher 14.7 volt charging, if that is what the shore charger is also doing. It is more likely to overcharge on a shallow discharge than a deep one, I think.

Have fun on your trip!

[MsNomer]

"I am a little surprised at the 14.7v for the absorption voltage, as it is right at the high limit of their specs."

I was surprised, too. The NOCO charges at max 14.8v. He was quite specific that any charger I use have this spec. Less was a no-go. This part of the conversation is what persuaded me to add solar--the alternator normally only goes to 14.3v.

[booster]

The 14.8 on the NOCO must be the end stage, after the normal absorption. I looked at the manual for a 30 amp version and they listed the absorption voltage at 14.4v. That would definitely explain the insistence on the extra time and cycle.

On the multibank NOCO, can you tie the banks together to get the higher output?

[MsNomer]

I don't understand your question

I was instructed to use the 12v/cold AGM setting.

[booster]

Originally Posted by MsNomer

I don't understand your question

When I looked at the NOCO site, all the single bank chargers were pretty low output. I think the biggest was 26 amps. They had bigger ones in multiband chargers. AGMs usually would prefer fairly fast charging in the range of 20% of capacity, so 200ah would be 40 amps. The NOCO seems to be very much like the Ctek chargers in that respect. Smallish chargers with lots of stages and automation, and specs that allow much larger battery banks than other brands of chargers of the same size.