roycv, thank you for detailing an aspect of SLA's that I didn't even think to mention...discharge current

My industrial experience when first introduced to SLA was their use in float charge/then fast discharge, as they were used to power indoor floodlights so that employees could escape from unlighted offices when the power went out. The escape lamps typically lasted only 20min...so that's a very fast discharge of a 4AHr battery, into an incandescent reflectored headlight bulb in a wall mounted bracket

The fact that they were found "everywhere" contributed to a lower price, as manufactured in very high volume.

Roy,

Many thanks for your excellent summary.

It seems many model boaters value ease of charging, weight and cheapness very highly.

While such attractions are very useful for tugs or scale freighters, they are less so for faster model boats of all kinds. Here the much faster discharge rate and power\ weight ratio of NiMH cells and especially LoOks come into their own!!

Again many thanks.

Dr John F Leeds and Bradford. MBC. 😊😐😊😐

Roy is absolutely correct. The link to PowerSonic battery site, which I previously posted, illustrates these rates for all the different size SLA's they offer. While not exactly spot on for all manufacturers, the rates are pretty close and provide a good guide line for our uses.
The site's charger listings also show the chargers rates and cut off slopes which, again, give a good illustration of the recommended charging parameters to use.
I am not says that these can only be used with PS products, but most of us are in the dark about the correct way to discharge and charge these batteries.
Lastly, please remember that the batteries DO have vents and therefore they are designed to be charged in the connector in the upright position. Otherwise the gas can not. will not, vent and the batteries increase the risk exploding at some point. More importantly, the efficiency of the battery drops and premature failure is the end result.😐

RodC tells us what he uses and maybe in general you may wonder why SLA's appear cheaper to buy. But I agree I use them for ballast too.
SLA's are rated at the 20 hour rate which means if you have a 5 amp hour (5Ahr.) capacity battery then the 5 amps has to be used over a 20 hour period. Might be a bit of a long day at the lake! To get the full capacity the current should be limited to 5 divided by 20 = 250 mAmps or 1/4 amps, not a lot!

Nimh and Nicad are rated at the 5 hour rate, the same rules apply so a 5Ahr battery can discharge at 1 amp for 5 hours. You pay more to get a higher discharge current.

There are SLA's that have the same ratings as NimH batteries and these are frequently cylindrical and are called Cyclon cells, they are as you might expect dearer than the other SLA's.

If you discharge a battery faster than the above calculation gives, then the efficiency of the battery decreases, notably in getting hot.

When a battery gets hot the energy that does this was part of the stored electrical energy in the battery i.e. the current that never reached the motor.

Perhaps you might like to check the batteries you use by running at full speed and check run time and compare this with slower running and pottering around to see the difference in the run times.

Hope this helps.

Roy

that's the problem with autocorrect especially if you can not spell worth a darnn😊

Hi Len,
"... only supplies a minuet amount of variable current ..."
Très musical. Minuet in G perhaps?😁
Otherwise I agree with you👍
I believe that such devices are also known as Battery Savers?
Cheers, Doug 😎

Hi Stephen T
I agree with johnf, RodC and roycv.
That said it also depends on the type of car battery charger you are using. I used a charger from the 1960's and it destroyed my 12v 12Ahr battery. I am aware that more modern car battery chargers are far more technical and this may be the type used by Colin H.
When I used to build my own chargers 14.1 volts was the max. A fully charged battery read as 13.5 volts.
I still use mine in my larger models as they provide useful ballast.
dave976

another item to consider is using a battery maintainer such as a "Battery Tender" by Deltran for long term storage of SLA batteries. This is NOT a trickle charger that is always putting a low level current into the battery but is a device that monitors the battery condition and only supplies a minuet amount of variable current to maintain the charge level of the battery. I may not have the correct description of how it does this but I thing you get the idea.
I use the battery tender on my custom street rod, blue car in my picture, as well as my 42" tug.

Hi just an addition to RodC's excellent response, Lead acid batteries are charged using the taper charge system. This means a fixed voltage is used as the charge voltage and as the battery increases its voltage with the charge the charge voltage difference reduces until there is just a trickle charge.

A trickle charge is a current of 1/10th the rated capacity of the battery. You can apply this for longer than necessary without worrying. There is an inherrant loss when charging a battery in all cases as you have to put in 40% more watts or energy than the battery can discharge.

The rated capacity of the battery is called C. So 1/10th. C is a trickle charge. In some cases there may be a suggested limit on the discharge current probably
5C or 5 times the capacity of the battery.
Using a battery to charge another battery is a big loss overall.

Most NiMh batteries are limited in some way the ones that can handle higher discharge currents have more connecting wires inside each cell to reduce the internal resistance. If interested, check out the maximum power theory.

regards

Roy

Yes, I use a 1amp trickle charger to restore my older batteries and my car battery charger for general charging and never had any issues with sla and gell type batteries.
Cheers Colin.

I agree with johnf's information. I wudnt even use a 2A/4A automotive charger on a motorcycle-size lead acid battery, it wud boil dry in short order.

I favour NiMH for light, quick boats as I am very comfortable with them, & SLA (sealed lead acid) where i need ballast. My newest Springer tug has two 6V/4Ahr SLAs wired in parallel into the ESC. All up she weighs 9lb. I charge them in parallel by setting a lab powersupply to 7.4V & then i short the powersupply leads together & adjust the current limit to 1.34A. I unshort the leads and apply them to the two batteries which are wired in parallel.

The max charge current will then be 1.34A (when the batteries are "dead" & the charge current will decrease as they approach the max charge voltage of 7.4V) Right now the supply is outputting 0.030A as they are just abt charged for my sail at 5:30 today in a recreation centre swimming pool

LiPO's make me nervous. I hav several stored in fireproof charging bags. They are used only in vessels that require their light weight, high energy density (for long running time), but there is not enough room left in the hull to carry around a 7.2V NiMH stick or two.

I bought the precision adjustable lab powersupply on AMAZON becuz i do a lot of electronics experiments plus I am an Amateur Radio Operator which is an experimental radio service.

Stephen,
I use PowerSonic batteries quite a bit. One of the reasons is because of the immense amount of information available, about their batteries and their charger, on their website, here:
https://www.power-sonic.com/batteries/ps-series/
When you "view" a battery, click on the tech spec data link. At the bottom of the next page will be the chargers recommended for that particular battery.
Then, go to the main menu and click on chargers and the specs on each charger, as well as it's charging profile is given.
There id far more to SLA's than most suspect and a lot of batteries get wasted thru misuse.
cheers😀

Hi Steven,

Definately not. Almost all car chargers push out at least 4 amps for 12 volt "wet" lead acid batteries - while almost all model boats use much smaller 6 volt " jelly" cells which are designed to be charged at a far slower rate.

Please check carefully and don't risk burning your workshop ( or even your house!!) down.

Dr John F. Leeds and Bradford. BBC. 👎👎👎☹️☹️