Potting, DC-DC converters Q

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niwrad   100 mW

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Potting, DC-DC converters Q

Post by niwrad » Jul 26 2019 2:14pm

Hello

https://www.ebay.com/itm/High-Voltage-E ... 749.l2649
I have the LiGo batteries from Grin and would like it to power the existing dynamo light on my bike as they seem to work fine, a Busch and Muller 6V light. I have bought some USB DC converters that ran 5, 9 and 12 V from a powerbank into the light. 9 and 12 V both produced the same level of brightness. The one from ebay i listed I got a 6V, and it's not as bright as 9/12V. I plan on gettiing the 9V version of the listed DC ebay buck converter

My question is, how do you waterproof something like the ebay converter? With the USB ones, it's all contained within the molded shell and I can cover it with electrical tape or perhaps silicone grease or silicone tape, but with the buck converter from ebay it's all exposed, and I'd like to cover it up in something like how the phase runners from grin are, or something similar.

Additionally I'd rather not use the USB ones, as it means it'll need a 5V battery source (or run the Grin 72V buck converter from the LiGos), but it's definitely something I could do

I couldn't find a buck converter that goes straight from 72 nominal battery (or 84+ for fully charged) down to the 6-9 volt range; that is also molded or covered. There are a bunch at 12 V though, but after experimenting with the USB DC DC converters, I found that there was no difference between 9 and 12 V, and I suspect there is an internal circuit in the light that prevents excessive current flow and indeed, I somehow shorted the light with a multimeter and it would not function until the capacitors running the standlight fully discharged overnight
Jersey City, New Jersey, USA

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E-HP   10 kW

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Re: Potting, DC-DC converters Q

Post by E-HP » Jul 26 2019 2:49pm

niwrad wrote:
Jul 26 2019 2:14pm
I couldn't find a buck converter that goes straight from 72 nominal battery (or 84+ for fully charged) down to the 6-9 volt range; that is also molded or covered.
Something like this won't work??
https://www.aliexpress.com/item/DC-step ... 00032.html

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fechter   100 GW

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Re: Potting, DC-DC converters Q

Post by fechter » Jul 26 2019 2:51pm

I had something similar and found a small plastic box it would fit into then filled the box with epoxy. It should work underwater now.
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niwrad   100 mW

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Re: Potting, DC-DC converters Q

Post by niwrad » Jul 26 2019 3:05pm

E-HP wrote:
Jul 26 2019 2:49pm
Something like this won't work??
https://www.aliexpress.com/item/DC-step ... 00032.html
I'm worried that full battery voltage might damage the device, since it only states it goes to 72V, but not necessarily up to 84V
Jersey City, New Jersey, USA

dustNbone   10 kW

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Re: Potting, DC-DC converters Q

Post by dustNbone » Jul 26 2019 3:36pm

You could also try just using an AC wall adapter that outputs the right voltage, connected straight to the battery most of these will work just fine. You might need to try switching polarity on the input to get it to go.

This is what I use for USB power on my bike, most of these adapters are pretty easy to seal up.

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amberwolf   100 GW

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Re: Potting, DC-DC converters Q

Post by amberwolf » Jul 27 2019 1:45am

There are a number of wifi router (netgear, etc) AC adapters that are 7.5vdc output at an amp or two. Many of them will work on a 50V+ battery, connecting one AC prong to positive, and the other to negative. Some will only startup if the battery is above 45-50V, but a 72v battery will be above that all the time, so would probably work fine. You can find htem at goodwill/etc for a buck or two, if you poke around. Probably available online for a few dollars more, but since you won't know which will startup on DC without testing, cheaper is better. ;)

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