Charging of AGM Deep Cycle Battery - Best Method??

thalls01 · Veteran Member

Charging of AGM Deep Cycle Battery - Best Method??

Peter_n_Margaret · Guru

AGM batteries do NOT benefit from cycling. They are best kept full.
You could use a very small solar panel on the shed roof to keep them topped up. A 5W panel would be plenty.
We have a polycarbonate panel in the roof of our shed. That allows sufficient sun through to keep the batteries charged using the solar panels on the vehicle.
Cheers,
Peter

PeterD · Guru

As P&M said, AGM batteries are happiest when kept full. Please scrap the ole duff gen you have been fed to one side.

"in the same fashion that a quality 8-stage charger does." There are only three important stages in a smart charger, bulk, absorption and float. The other five are just frills, some of them are handy if you are the type that fully discharge your batteries. If you are not one of those then they are of little importance.

If you have a look at the handbook of your BMPro unit you will see it has many of those frill stages. The absorption and float voltages are suitable for AGM batteries. The only problem with it is that the battery charging current is not particularly great so do not expect rapid charging of your batteries. If you do flatten your batteries it may take more than one night to recharge your batteries fully. Otherwise, the charger is suitable for your situation.

Hitting the road · Senior Member

I took out the small 100 amp AGM supplied with my Jayco and put in 2 x 140 amp AGM's The built in BMPRO BMS multi stage charger is fine to keep them charged while parked up. I keep mine on charge 24/7 between uses.

As written above, an AGM battery or any battery for that matter generally has a life span based on drain and recharge cycles. The old "trickle charge" of years gone by to maintain a wet battery is old school, A modern AGM battery is very happy fully charged, only accepting what it needs to maintain that state of charge.

Whenarewethere · Guru

If one adds up the total life cycle AH, there is not a lot of difference is total cycles of amps whether you drain the battery a bit or a lot. Look at the data sheet of the battery (multiply % drain X cycles)

So if you drain the battery a lot once a month it really will not affect its long term life, as other you will be only using a bit.

thalls01 · Veteran Member

Hi members
I value your feedback and corrections.

I firmly have entrenched now that AGM batteries do not require cycling and can tolerate being fully charged between camping expeditions.

Good to learn also from 'Hitting the Road" that his BMPROBatteryPlus35 unit is powering both 140Ah batteries 24/7 without issue. I believe the BMPROBatteryPlus35 can charge up to 600Ah worth of batteries.

I had BMPRO forward me the electronic manual for the BMPROBatteryPlus35 overnight, since I never received the manual for it or the TREK3 monitor when purchasing the van late last year.

I might consider P & M's suggestion of trickle charging the AGM batteries from a regulated 5 watt panel fitted to the rooftop when the caravan is in storage.

Peter_n_Margaret · Guru

thalls01 wrote:
I might consider P & M's suggestion of trickle charging the AGM batteries from a regulated 5 watt panel fitted to the rooftop when the caravan is in storage.

A 5W solar panel is small enough that it does not need regulaing. Just don't be tempted to use a bigger one. Smaller would be OK too.

Cheers,

Peter

Cupie · Guru

I fully agree with both Peters on this issue.

For convenience I keep my van AGM on float via its multistage smart charger, but do use a small solar panel to keep the rarely used Patrol's battery on charge. If I were really serious about it I would go to the trouble of installing a second small solar panel for the van, but its parking location is not readily conducive to that option.

My set up has worked well for decades.

Cuppa · Guru

There are two schools of thought on the best way to manage AGM batteries when not in use. One says charge them until they drop into float & then switch off charger for a month or three, then repeat. The other says charge them fully & leave them on float (same as charging them fully & then putting them on a small solar trickle charger). I have done both to various AGM batteries over the years & have had a minimum battery life of just under 10 years & an unknown maximum (I sold the vehicle) exceeding 12 years. My conclusion is that either way works.

FWIW AGM's were originally designed for military purposes, when the military wanted vehicles which could sit for long periods unused with minimal maintenance but be ready for use at very short notice.

In one vehicle I had a large Ctek charger which would automatically revert to bulk mode charging every 10 days (IIRC) - however it also had a power supply mode, so I would charge the batteries to float & then change it to power supply mode for the longer term to avoid unnecessary cycling. Power supply mode was 13.3v.

thalls01 · Veteran Member

Cupie & Cuppa - thanks for your methodologies and advice per charging of AGM batteries in storage. I will probably use a max. 5 watt unregulated solar cell to trickle charge them to maintain 'float' as P&M suggested.

I also want to acknowledge PeterD's advice about using the BMPRO BatteryPlus35 to charge a flat/multiple flat AGM batteries. The BMPRO BatteryPlus35 is rated at 30 amp max. so understandably it will take time to return the batteries to full charge at float, if flattened.

I can connect a portable solar cell of between 180 to 300 watts directly to one or more AGM batteries via a MPPT device with a higher current with the use of a BC300 shunt to the BMPRO BatteryPlus35 for a voltage reading. In reality however, I believe the cost of the MPPT device of say 50 amps or more throughput may be excessive and could shelve this prospect.

Query: Have others a view on the merits of purchasing a high amperage MPPT device for this purpose, and were the benefits borne out in reality?

Query: Related to MPPT devices, does anyone have a preferential brand name for MPPT device?

Cheers, Tim

PeterD · Guru

thalls01 wrote:
I also want to acknowledge PeterD's advice about using the BMPRO BatteryPlus35 to charge a flat/multiple flat AGM batteries. The BMPRO BatteryPlus35 is rated at 30 amp max. so understandably it will take time to return the batteries to full charge at float, if flattened.

The charge current from the mains power is not 30 A. From the handbook I have downloaded:

Note: This battery charger is rated to charge lead acid battery banks of up to 300 Ah capacity.
Charging current is limited to 20A. Refer to About the BatteryPlus35 Power Supply.

The only reference to 30 A charging is:

Solar Panel Connection
BatteryPlus35 optionally is available with a solar input. Standard 12V solar panels are to be
connected to this input. This input is internally connected to a Maximum Power Point Tracking
(MPPT) charger which is able to charge a 12V battery system and provide power to the loads.
This MPPT charger is a smart, multistage, 450W regulator which is capable of delivering up-to
30A. The charging stages are described in Figure 6: Charging Algorithm.

Does your unit include the MPPT charger?

thalls01 · Veteran Member

PeterD, I was referring to the solar input to the BatteryPlus35 when off-roading. Your qualification that 30A in not attainable via powered 240V mains is correct.

Either means of charging is a lot slower than using a higher amp rated MPPT device connected directly to the AGM deep cycle battery, as far as I can determine.

Also if I connect a 2nd PORTABLE solar panel rated at 300 watts directly to the BatteryPlus35 system with my current fixed 150 watt panel to the caravan roof, I will only get a further 150 watts rather than the portable panel's 300 watts. That is, the 2nd solar panel's capacity to charge is reduced to the same wattage at the 1st panel by the BatteryPlus35 according to BMPRO.

Hence the preference to connect directly to the battery with a higher amperage MPPT device whilst using a BC300 shunt to the BatteryPlus35 to obtain an accurate voltage reading from the AGM battery.

Cheers and thanks, Tim

Jaahn · Guru

thalls01 wrote:
------------

Query: Have others a view on the merits of purchasing a high amperage MPPT device for this purpose, and were the benefits borne out in reality?

Query: Related to MPPT devices, does anyone have a preferential brand name for MPPT device?

Cheers, Tim

Hi Tim smile

There is a discussion about MPPT charger brands in this thread in the Solar Power sub forum above ; https://thegreynomads.activeboard.com/t68205633/cheap-mppt-recommendations/

Jaahn

Just ignore the garage door hijack discussion

-- Edited by Jaahn on Monday 21st of March 2022 08:02:18 AM